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Short report: Proximity to mosquito breeding sites as a risk factor for clinical malaria episodes in an urban cohort of Ugandan children
Abstract
The impact of geography on incidence of clinical episodes of malaria was investigated in a cohort of children enrolled in a longitudinal clinical trial of antimalarial therapy in Kampala, Uganda. Participant households and the boundaries of local swamps and streams were mapped and incidence of clinical malaria episodes was measured prospectively using passive surveillance during one year of follow-up. Of 316 cohort participants, 305 from 219 households were followed for at least six weeks and were included in the analysis. Incidence of clinical malaria was highly variable, with no episodes occurring in 131 participants, and 367 new episodes of malaria diagnosed in the remaining 174 children. A gradient in incidence of clinical episodes of malaria was observed with distance of residence from a swamp (0.41 episodes per person year for residence > 100 meters from a swamp increasing to 2.22 episodes per person year for residence within a swamp), or a stream (0.61 episodes per person year for residence > or = 500 meters from a stream versus 1.76 episodes per person year for residence <500 meters from a stream). Multivariate analysis showed that distances of residence from a swamp or from a stream were independent predictors of malaria incidence, controlling for age, use of preventative measures, and primary source of water. Distance from a swamp was the strongest predictor, with an incidence rate ratio of 4.3 (95% confidence interval = 2.6-6.9, P < 0.001) between residence within a swamp and >100 meters from a swamp. In this urban setting, incidence of clinical episodes of malaria was strongly associated with proximity of residence to potential mosquito breeding sites.
... In the mortality analysis in this study we include the geographic context variable distance to wetland; the rationality of including this variable is that malaria was present in the study area at that time and also that several studies have found increased risk of malaria due to proximity to wet areas (Staedke et al. 2003;Zhou et al. 2007;Parker et al. 2015). Most commonly, distances are defined as Euclidian distance from place of residence, such as houses in Zhou et al. (2007), neglecting movement of people (cf. ...
... Furthermore, distances in epidemiological and demographic research are either defined on interval scale (e.g., Pezeshki et al. 2012) or on ordinal scale (using distance intervals, cf. Staedke et al. 2003). ...
Geocoding longitudinal and individual-level historical demographic databases enables novel analyses of how micro-level geographic factors affected demographic outcomes over long periods. However, such detailed geocoding involves high costs. Additionally, the high spatial resolution cannot be properly utilized if inappropriate methods are used to quantify the geographic factors. We assess how different geocoding levels and methods used to define geographic variables affects the outcome of detailed spatial and historical demographic analyses. Using a longitudinal and individual-level demographic database geocoded at the property unit level, we analyse the effects of population density and proximity to wetlands on all-cause mortality for individuals who lived in five Swedish parishes, 1850–1914. We compare the results from analyses on three detailed geocoding levels using two common quantification methods for each geographic variable. Together with the method selected for quantifying the geographic factors, even small differences in positional accuracy (20–50 m) between the property units and slightly coarser geographic levels heavily affected the results of the demographic analyses. The results also show the importance of accounting for geographic changes over time. Finally, proximity to wetlands and population density affected the mortality of women and children, respectively. However, all possible determinants of mortality were not evaluated in the analyses. In conclusion, for rural historical areas, geocoding to property units is likely necessary for fine-scale analyses at distances within a few hundred metres. We must also carefully consider the quantification methods that are the most logical for the geographic context and the type of analyses.
... [3] Although Anopheles mosquitoes are known to be able to fly considerable distances (several km) [4,5], they will prefer available hosts close to their breeding sites. [6,7] A wide variety of human factors such as body size, bed net usage, time spent outdoors, quality of housing and even beer-consumption has previously been shown to affect human susceptibility to mosquito bites. [8][9][10][11] Another important factor contributing to the heterogeneity of transmission is the very variable and difficult-to-quantify duration of infection in humans. ...
... [28] Using a spatial mathematical transmission model that allows for the transmission of multiple parasite clones, we therefore investigated whether spatially heterogeneous human and mosquito populations better explain the observed mean MOI vs. mean parasite prevalence relationship. [3,7,16,23,29] Based on the underlying spatial distributions of human and mosquito populations, limited mixing between these populations will arise from i) the constrained radius of mosquito flight and ii) the distance dependent movement of human individuals. [29,30] Coupled with other factors (some mentioned above) that determine human exposure, this will inherently result in a small proportion of the population receiving most mosquito bites. ...
As malaria is being pushed back on many frontiers and global case numbers are declining, accurate measurement and prediction of transmission becomes increasingly difficult. Low transmission settings are characterised by high levels of spatial heterogeneity, which stands in stark contrast to the widely used assumption of spatially homogeneous transmission used in mathematical transmission models for malaria. In the present study an individual-based mathematical malaria transmission model that incorporates multiple parasite clones, variable human exposure and duration of infection, limited mosquito flight distance and most importantly geographically heterogeneous human and mosquito population densities was used to illustrate the differences between homogeneous and heterogeneous transmission assumptions when aiming to predict surrogate indicators of transmission intensity such as population parasite prevalence or multiplicity of infection (MOI). In traditionally highly malaria endemic regions where most of the population harbours malaria parasites, humans are often infected with multiple parasite clones. However, studies have shown also in areas with low overall parasite prevalence, infection with multiple parasite clones is a common occurrence. Mathematical models assuming homogeneous transmission between humans and mosquitoes cannot explain these observations. Heterogeneity of transmission can arise from many factors including acquired immunity, body size and occupational exposure. In this study, we show that spatial heterogeneity has a profound effect on predictions of MOI and parasite prevalence. We illustrate, that models assuming homogeneous transmission underestimate average MOI in low transmission settings when compared to field data and that spatially heterogeneous models predict stable transmission at much lower overall parasite prevalence. Therefore it is very important that models used to guide malaria surveillance and control strategies in low transmission and elimination settings take into account the spatial features of the specific target area, including human and mosquito vector distribution.
... An important message addressed in the Pretoria Statement on urban malaria was that the malaria control strategies used in rural areas cannot be directly transferred to the urban context (Donnelly et al., 2005). The epidemiology of urban malaria poses a number of specific challenges: i) the first malaria infection occurs often late in childhood and the acquisition of semi-immunity is delayed ; ii) the intensity of the malaria risk is often heterogeneous over small distances, being subjected to the degree of urbanization of particular subdivisions (Robert et al., 2003;Trape and Zoulani, 1987) and their proximity to possible vector breeding sites (Staedke et al., 2003;Trape et al., 1992); iii) rural-urban migration is likely to increase the endemicity of malaria (Benyoussef et al., 1976); iv) agricultural and animal husbandry are important economic activities which create a favourable environment for Anopheles breeding (Afrane et al., 2004;Robert et al., 1998); v) marginalized populations usually lack access to health care, which hampers the effectiveness of case management and the promotion of intermittent antimalarials during pregnancy (Donnelly et al., 2005;Massele et al., 1997;Noor et al., 2003;Sanon, 1999). There is now substantial private sector activity in health care provision in many cities. ...
... In the health facility-based surveys, it was found that the water supply types (fountains or streams) and the proximity to home gardening fields were associated with malaria infection. This association was noted as well in Uganda (Staedke et al., 2003) and Dar es Salaam . ...
... The explicit control of hydrology and geomorphology on the formation of malaria vector habitats means that their distribution will be heterogeneous, enabling the identification of hotspots. This has been exploited in studies that associate malaria transmission rates to proximity to marshland or swamps which tend to be found in areas of topographic convergence, such as valley bottoms, for example in the Western Kenyan Highlands and the Usambara Mountains, Tanzania [21][22][23][24][25][26][27][28]. ...
... This reflects the influence of subterranean processes governing the movement of water on Unguja through the karst landscape via an aquifer network or the concentration of water bodies in localised areas of low infiltration, such as doline features infilled with fine grained material. This is in contrast to other, non-karst landscapes, such as the Western Kenyan Highlands and the Usambara Mountains, Tanzania, are dominated by the overland, or near-surface movement of water, resulting in an association between elevation and/or terrain and malaria transmission [21][22][23][24][25][26][27][28]. ...
Background
Larval source management strategies can play an important role in malaria elimination programmes, especially for tackling outdoor biting species and for eliminating parasite and vector populations when they are most vulnerable during the dry season. Effective larval source management requires tools for identifying geographic foci of vector proliferation and malaria transmission where these efforts may be concentrated. Previous studies have relied on surface topographic wetness to indicate hydrological potential for vector breeding sites, but this is unsuitable for karst (limestone) landscapes such as Zanzibar where water flow, especially in the dry season, is subterranean and not controlled by surface topography.Methods
We examine the relationship between dry and wet season spatial patterns of diagnostic positivity rates of malaria infection amongst patients reporting to health facilities on Unguja, Zanzibar, with the physical geography of the island, including land cover, elevation, slope angle, hydrology, geology and geomorphology in order to identify transmission hot spots using Boosted Regression Trees (BRT) analysis.ResultsThe distribution of both wet and dry season malaria infection rates can be predicted using freely available static data, such as elevation and geology. Specifically, high infection rates in the central and southeast regions of the island coincide with outcrops of hard dense limestone which cause locally elevated water tables and the location of dolines (shallow depressions plugged with fine-grained material promoting the persistence of shallow water bodies).Conclusions
This analysis provides a tractable tool for the identification of malaria hotspots which incorporates subterranean hydrology, which can be used to target larval source management strategies.
... 52 The current study revealed that the proximity of water body within less than 2 km to home increased odds of malaria morbidity than children with their home located beyond 2 km from the water body. This study was similar with the findings from southwest Ethiopia, 15 Uganda, 53 and Cameroon. 54 It is the fact that the open water sources such as rivers, swamps, and stagnant water may ultimately become the ideal mosquito breeding habitats. ...
Background:
Understanding the determinants of malaria morbidity offers helpful insights toward the changing malaria situation, which might lead to the adjustment of malaria program activities. Even though the determinants of malaria morbidity remain unknown, school-aged children were the highest malaria morbidity contributors in the East Hararghe Zone. Therefore, this study aimed to assess the determinants of malaria morbidity among school-aged children in the study area from February 1 to May 31, 2020.
Methods:
A case-control study was conducted among school-aged children living in ten randomly selected low, moderate, and high malaria transmission kebeles. Cases were confirmed as positive for malaria, while controls were confirmed as negative for malaria among randomly selected school-aged children. Rapid diagnostic testing (RDT) and blood film (BF) malaria testing methods were used. Multivariable logistic regression was used to identify association between malaria and its determinants.
Results:
The determinants of malaria infection were having no formal education (adjusted odds ratio (AOR)=4.91, 95% CI: 1.20-20.17), low family wealth index (AOR=2.50, 95% CI: 1.22-5.12), being from rural residence (AOR=2.34, 95% CI: 1.87-4.12), living near to stagnant water (AOR=2.01, 95% CI: 1.14-3.54), having a maximum of three family members (AOR=0.37, 95% CI: 0.18-0.78), using indoor residual spraying (IRS) (AOR=0.15, 95% CI: 0.08-0.29) and long-lasting insecticide-treated net (LLITN) over the last night (AOR=0.19, 95% CI: 0.10-0.35), and living in the house surrounded by cultivated land(AOR=0.24, 95%CI: 0.10-0.60) compared with their counterparts.
Conclusion:
This study revealed that residence, family size, education, wealth index, stagnant water existence, and using LLITN and IRS had significant association with malaria morbidity. Thus, all concerned bodies, including the community should strengthen working on stagnant water elimination around their house to cut the breeding site of the malaria vector mosquito. Moreover, the findings have an important implication for improving interventions targeting the economic status and literacy of the society that may help in the reduction of the risk of malaria in the school-aged children.
... Furthermore, it agrees with this study that the individuals with higher levels of education are likely to be employed or in business and therefore can easily access healthcare services or afford the use of other preventive measures such as indoor residual spray (IRS) among others. Our results are by and large consistent with the fact that the risk of contracting malaria disease is strongly associated with closeness to the breeding areas (29). (16). ...
Globally, about 3 billion individuals are at peril of contracting malaria disease annually. This disease load is intensified by the fact that about 2-3 million children are infected with HIV in sub-Saharan Africa. Malaria and HIV coinfection is rampant in the region and account for significant morbidity and mortality. Among the malaria causing parasites species, Plasmodium falciparum causes more severe form of malaria disease. This study determined prevalence of malaria disease by age, gender, residence; severity by species and its determinants among HIV infected and HIV non-infected children less than 5 years in Kisumu County. All the data analysis was conducted in Stata version 14. A total of 132 study participants were recruited with equal distribution of sero-status, HIV+ (n=66) and HIV-(n=66). The mean (SD) age of HIV-infected children was 3.01(0.95) years (range 1.5-5.0 years) while the SD age for the HIV non-infected children was 2.59 (1.21) years (range: 0.3-5.0 years). Out of the 66 non-HIV infected children, 21.21 % (95%CI=0.13-0.33) had P. falciparum and 6.06% (0.02-0.15) had P. malariae. Among the HIV infected children, 4.55% (95%CI=0.01-0.13) had P. falciparum while 1.52 % (95%CI= 0.00-0.10) had P. ovale. The prevalence was highest in children 4 to 5 years old with 37.50 (95%CI=0.17-0.64) among HIV non-infected. Severity of disease was classified based on Lambaréné´ Organ Dysfunction Score (coma, prostration, or deep breathing), LODS >0 (2.27% (95%CI=0.01-0.07). The study concluded that LODS is a clinical predictor of severity of disease (malaria) and its assessment should be implemented by the primary healthcare provider. Similarly increased uptake of Cotrimoxazole prophylaxis coupled with methodical clinical checkups contributed to the reduction in malaria infection in HIV infected children.
... arabiensis was significantly higher in clusters close to the river compared to clusters away from the river. This could be explained by the availability of breeding sites in riverbeds [19,[45][46][47][48]. ...
Background
Understanding malaria vector’s population dynamics and their spatial distribution is important to define when and where the largest infection risks occur and implement appropriate control strategies. In this study, the seasonal spatio-temporal dynamics of the malaria vector population and transmission intensity along intermittent rivers in a semi-arid area of central Ethiopia were investigated.
Methods
Mosquitoes were collected monthly from five clusters, 2 close to a river and 3 away from a river, using pyrethrum spray catches from November 2014 to July 2016. Mosquito abundance was analysed by the mixed Poisson regression model. The human blood index and sporozoite rate was compared between seasons by a logistic regression model.
Results
A total of 2784 adult female Anopheles gambiae sensu lato (s.l.) were collected during the data collection period. All tested mosquitoes (n = 696) were identified as Anopheles arabiensis by polymerase chain reaction. The average daily household count was significantly higher (P = 0.037) in the clusters close to the river at 5.35 (95% CI 2.41–11.85) compared to the clusters away from the river at 0.033 (95% CI 0.02–0.05). Comparing the effect of vicinity of the river by season, a significant effect of closeness to the river was found during the dry season (P = 0.027) and transition from dry to wet season (P = 0.032). Overall, An. arabiensis had higher bovine blood index (62.8%) as compared to human blood index (23.8%), ovine blood index (9.2%) and canine blood index (0.1%). The overall sporozoite rate was 3.9% and 0% for clusters close to and away from the river, respectively. The overall Plasmodium falciparum and Plasmodium vivax entomologic inoculation rates for An. arabiensis in clusters close to the river were 0.8 and 2.2 infective bites per person/year, respectively.
Conclusion
Mosquito abundance and malaria transmission intensity in clusters close to the river were higher which could be attributed to the riverine breeding sites. Thus, vector control interventions including targeted larval source management should be implemented to reduce the risk of malaria infection in the area.
... Unpaved roads and poor quality housing in low socioeconomic environments particularly in the peripheries of the cities create a conducive environment for the malaria vectors to thrive [10][11][12][13]. The adaptation of malaria vectors to urban ecosystems warrants close attention in sub-Saharan Africa [4]. ...
Background: Malaria is traditionally known to be concentrated in rural areas but the disease is increasingly becoming a major public health problem for urban settlements in Africa. National malaria reports show that Mutare City had the greatest endemic malaria burden among all urban settlements in Zimbabwe. To prevent malaria outbreaks, it is essential to monitor malaria vectors in populous urban centers to establish the foci of the vectors while they are still small. This study sought to identify, describe, quantify, geocode mosquito potential larval habitats and their spatial distribution within the city.
Methods: Mutare City was divided into four regions and the study was conducted from June to November 2019. Larval sampling of 223 potential habitats was done and the collected larvae were reared until they became adult mosquitoes before being morphologically identified using the keys developed by Gillies and Coetzee. Data were entered and analyzed using Epi Info version 7.2.1.0 statistical package.
Results: Anopheline speciation showed that the city was infested with Anopheles funestus (4.9%), An. arabiensis (0.3%), An. pretoriensis (91.3%) An. coustani (0.5%), An. rufipes (2.8%), and An. maculipalpis (0.2%). Overall, An. funestus group was the predominant with An. arabiensis complex less common. The species composition of An. funestus group varied significantly among the sampling habitats. Results showed most mosquito breeding habitats were due to human activities such as agriculture, earth mining, and leaking piped water valves. The digging of shallow wells for domestic use in the high-density areas also contributed to the increase in mosquito breeding habitats.
Conclusion: The most significant malaria vectors in the city were An. funestus ss and An. arabiensis. The proliferation of larval habitat hotspots in Mutare City was being fueled by human activities related to earning a living and housing construction. Effective interventions for enhanced larval source management could use a multi-sectoral approach involving all the urban stakeholders. Considering the rapid expansion of the city, more investment is needed to target the most productive habitats by fixing leaking water pipes and frequent application of larvicides with greater residual activity to treat permanent habitats particularly before the rainy season.
... The number of cases decreased gradually with distance. Consequently, the areas most exposed to the risk of malaria transmission can be considered as those close to the main water retention areas and the most remote neighborhoods with soils that retain less water are the least exposed [21,37]. ...
Despite the deployment of several effective control interventions in central-western Sene-gal, residual malaria transmission is still occurring in some hotspots. To better tailor targeted control actions, it is critical to unravel the underlying environmental and geographical factors that cause the persistence infection in hotspot villages. "Hotspots villages" were defined in our study as those reporting more than six indigenous malaria cases during the previous year. A total of ten villages, including seven hotspots and three non-hotspots, were surveyed. All potential mosquito breeding sites identified in and around the ten study villages were regularly monitored between 2013 and 2017. Monitoring comprised the detection of anopheline larvae and the collection of epidemiological, hydrogeological, topographical, and biogeographical data. The number of larval breeding sites described and monitored during the study period ranged from 50 to 62. Breeding sites were more numerous in hotspot sites in each year of monitoring, with 90.3% (56/62) in 2013, 90.9% (50/55) in 2014, 90.3% (56/ 62) in 2015 and 86% (43/50) in 2017 (Fisher exact test; p = 1). In the non-hotspot areas, the data for the same years were, respectively, 9.7% (6/62), 9.1% (5/55), 9.7% (6/62) and 14% (7/50) (p = 1). The Hotspot villages were characterized mostly by saline or moderately saline hydro-morphic and halomorphic soils allowing water retention and a potential larval breeding sites. By contrast, non-hotspot villages were characterized mainly by a high proportion of extremely permeable sandy-textured soils, which due to their porosity had low water retention. The annual number of confirmed malaria cases was correlated with the frequency and extent of breeding sites. Malaria cases were significantly more frequent in the hamlets located near breeding sites of An. gambiae s.l., gradually decreasing with increasing remoteness. This study shows that the characteristics of larval breeding sites, as measured by their longevity, stability, proximity to human habitation, and their positivity in Anopheles larvae are likely determining factors in the persistence of malaria hotspots in central-western Senegal. The results of this study shed more light on the environmental factors underlying PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.
... Informal settlements have been built in vicinity of marshes, streams and swamps because of their high viability for urban agriculture [43]. This influences the intra-urban spatial heterogeneity and is consistently implicated in increased malaria prevalence in these areas [44,45]. In addition, the sanitation conditions of the city's slums tend to deteriorate during the peak of the wet season in which malaria transmission intensifies [46]. ...
Background:
The rapid and often uncontrolled rural-urban migration in Sub-Saharan Africa is transforming urban landscapes expected to provide shelter for more than 50% of Africa's population by 2030. Consequently, the burden of malaria is increasingly affecting the urban population, while socio-economic inequalities within the urban settings are intensified. Few studies, relying mostly on moderate to high resolution datasets and standard predictive variables such as building and vegetation density, have tackled the topic of modeling intra-urban malaria at the city extent. In this research, we investigate the contribution of very-high-resolution satellite-derived land-use, land-cover and population information for modeling the spatial distribution of urban malaria prevalence across large spatial extents. As case studies, we apply our methods to two Sub-Saharan African cities, Kampala and Dar es Salaam.
Methods:
Openly accessible land-cover, land-use, population and OpenStreetMap data were employed to spatially model Plasmodium falciparum parasite rate standardized to the age group 2-10 years (PfPR2-10) in the two cities through the use of a Random Forest (RF) regressor. The RF models integrated physical and socio-economic information to predict PfPR2-10 across the urban landscape. Intra-urban population distribution maps were used to adjust the estimates according to the underlying population.
Results:
The results suggest that the spatial distribution of PfPR2-10 in both cities is diverse and highly variable across the urban fabric. Dense informal settlements exhibit a positive relationship with PfPR2-10 and hotspots of malaria prevalence were found near suitable vector breeding sites such as wetlands, marshes and riparian vegetation. In both cities, there is a clear separation of higher risk in informal settlements and lower risk in the more affluent neighborhoods. Additionally, areas associated with urban agriculture exhibit higher malaria prevalence values.
Conclusions:
The outcome of this research highlights that populations living in informal settlements show higher malaria prevalence compared to those in planned residential neighborhoods. This is due to (i) increased human exposure to vectors, (ii) increased vector density and (iii) a reduced capacity to cope with malaria burden. Since informal settlements are rapidly expanding every year and often house large parts of the urban population, this emphasizes the need for systematic and consistent malaria surveys in such areas. Finally, this study demonstrates the importance of remote sensing as an epidemiological tool for mapping urban malaria variations at large spatial extents, and for promoting evidence-based policy making and control efforts.
... This negative impact is consistent with the empirical findings that proximity to polluted watercourses generally induces disamenities (Cho, Roberts, & Kim, 2011;Netusil, Kincaid, & Chang, 2014;Chen, 2017). Examples of these disamenities include those generated by the malodour diffused from the polluted water (Sheng et al., 2008;Liang, An, Li, & Zhang, 2015) and the potential health risks of infectious diseases associated with excessive mosquitoes using the River as their breeding habitat (Staedke et al., 2003;Li et al., 2014;Munch, Nielsen, Racz, & Hjalager, 2016). But intriguingly, the marginal implicit price discount of proximity to the Zengbu River is much smaller than another two streams in Guangzhou (RMB 44,342 for the Huangpu Stream and RMB 71,153 for the Chigang Stream), as reported by Chen and Li (2017). ...
... A recent study reported an increase in prevalence of An. punctulatus and a decrease of An. koliensis, another late biter, in an adjacent area in East Sepik province, as well as a shift to earlier mean biting times of An. punctulatus in addition to significantly reduced manbiting-rates and annual entomological inoculation rates after the LLIN campaign [48]. Proximity to vector-breeding sites is related to the risk of malaria and can also be a main driver of heterogeneity [49][50][51], but was not investigated in the current study. Cultural factors, socio-economic status and education level play an additional role in risk of infection and can vary across villages and households, as well as human behavioural and genetic factors [9,21,28,[52][53][54][55][56]. ...
Background:
In the past decade, national malaria control efforts in Papua New Guinea (PNG) have received renewed support, facilitating nationwide distribution of free long-lasting insecticidal nets (LLINs), as well as improvements in access to parasite-confirmed diagnosis and effective artemisinin-combination therapy in 2011-2012.
Methods:
To study the effects of these intensified control efforts on the epidemiology and transmission of Plasmodium falciparum and Plasmodium vivax infections and investigate risk factors at the individual and household level, two cross-sectional surveys were conducted in the East Sepik Province of PNG; one in 2005, before the scale-up of national campaigns and one in late 2012-early 2013, after 2 rounds of LLIN distribution (2008 and 2011-2012). Differences between studies were investigated using Chi square (χ2), Fischer's exact tests and Student's t-test. Multivariable logistic regression models were built to investigate factors associated with infection at the individual and household level.
Results:
The prevalence of P. falciparum and P. vivax in surveyed communities decreased from 55% (2005) to 9% (2013) and 36% to 6%, respectively. The mean multiplicity of infection (MOI) decreased from 1.8 to 1.6 for P. falciparum (p = 0.08) and from 2.2 to 1.4 for P. vivax (p < 0.001). Alongside these reductions, a shift towards a more uniform distribution of infections and illness across age groups was observed but there was greater heterogeneity across the study area and within the study villages. Microscopy positive infections and clinical cases in the household were associated with high rate infection households (> 50% of household members with Plasmodium infection).
Conclusion:
After the scale-up of malaria control interventions in PNG between 2008 and 2012, there was a substantial reduction in P. falciparum and P. vivax infection rates in the studies villages in East Sepik Province. Understanding the extent of local heterogeneity in malaria transmission and the driving factors is critical to identify and implement targeted control strategies to ensure the ongoing success of malaria control in PNG and inform the development of tools required to achieve elimination. In household-based interventions, diagnostics with a sensitivity similar to (expert) microscopy could be used to identify and target high rate households.
... The proximity to Lake Zeway or the Bulbula River, which have the most confirmed breeding sites [23,50], increased the risk of malaria clustering at individual and village level analysis. Previous studies also have reported that close proximity to these sites increases the risk of malaria infection and clustering [19,48,[51][52][53][54]. It is not a surprise to see higher risk of infection in a locality near breeding site of potentially infective Anopheles mosquitoes [13]. ...
INTRODUCTION:Understanding the spatiotemporal clustering of malaria transmission would help target interventions in settings of low malaria transmission. The aim of this study was to assess whether malaria infections were clustered in areas with long-lasting insecticidal nets (LLINs) alone, indoor residual spraying (IRS) alone, or a combination of LLINs and IRS interventions, and to determine the risk factors for the observed malaria clustering in southern-central Ethiopia. METHODS:A cohort of 34,548 individuals residing in 6,071 households was followed for 121 weeks, from October 2014 to January 2017. Both active and passive case detection mechanisms were used to identify clinical malaria episodes, and there were no geographic heterogeneity in data collection methods. Using SaTScan software v 9.4.4, a discrete Poisson model was used to identify high rates of spatial, temporal, and spatiotemporal malaria clustering. A multilevel logistic regression model was fitted to identify predictors of spatial malaria clustering. RESULTS:The overall incidence of malaria was 16.5 per 1,000 person-year observations. Spatial, temporal, and spatiotemporal clustering of malaria was detected in all types of malaria infection (P. falciparum, P. vivax, or mixed). Spatial clustering was identified in all study arms: for LLIN + IRS arm, a most likely cluster size of 169 cases in 305 households [relative risk (RR) = 4.54, P
... The findings were endorsed by other studies in Uganda, Ethiopia, Cameroon and Sri Lanka. The studies found an increased risk of acquiring malaria among people living around mosquito breeding sites [7,[16][17][18][19]. ...
Background and Aim: Malaria remains a major public health problem and a global threat to humanity especially in sub-Saharan Africa. In a bit to combat malaria in Cameroon, about 8million Cameroonian received the insecticide treated nets (ITNs) in 2011. However, hospital based reported prevalence of malaria still remains high. Our objective was to determine the community based prevalence and possible risk factors of malaria in pregnancy in the Mamfe health district, south west region-Cameroon.
Methods: This was a community-based cross-sectional study involving 269 pregnant women in the Mamfe health district of Cameroon. Three out of the 5 health areas were randomly selected and pregnant women were later sampled by convenience and an interviewer administered questionnaire was done. Also rapid diagnostic test (RDT) for malaria was done for all the participants. Data was analysed using Epi info version 3.5.4 at a level of error of 5%. Results: Of the 269 pregnant women who took part in the study, 106 (39.6%) were positive for malaria. Risk factors associated with developing malaria among them were: presence of mosquito breeding sites (OR=0.001, 95%CI; 0.02-0.27, p-value=0.001), not sleeping under Insecticide treated nets(ITNs) (OR=0.01, 95%CI; 0.01-0.03, p-value=0.001), bushes around houses (OR=0.24, 95%CI; 0.07-0.79, p-value=0.02) and not taking intermittent preventive treatment (IPT) (OR=0.08, 95%CI; 0.01-0.49 p-value=0.01). Majority of participant knew malaria can be prevented by sleeping under ITNs 75% (95%CI; 69.9-80.5) and uptake of IPT 23.8% (95%CI; 18.8-29.2).
Conclusion: Prevalence of malaria in pregnancy in the Mamfe health district is higher than reported by the regional delegation of public health for the south west. Risk factors include: mosquito breeding sites, bushes around compound, not taking IPT and none use bed nets are known to pregnant women. Interventions to fight against malaria in pregnancy should target intensification of health education on environmental hygiene and use of ITNs.
... Adicional a esto se incluye que para malaria el estatus socioeconómico bajo, prácticas urbanas de agricultura y una deficiente vigilancia del uso de la tierra contribuye con el aumento de la transmisión (52), debido a que permiten el aumento de sitios de cría en las franjas urbanas y el aumento del contacto vector-humano debido a que los vectores se adaptan a los ecosistemas urbanos (53). En las áreas urbanas las fuentes de sangre son estables y abundantes, pero la dispersión de los vectores es baja y la transmisión de la malaria está asociada a la proximidad de los sitios de cría (54,55). El riesgo de la malaria en estas zonas es muy heterogéneo en el área de influencia por lo que puede variar entre vecindarios (56,57), como fue establecido en Ghana (58). ...
El plan decenal de Salud Publica 2012-2021 se estableció para lograr equidad en salud y adopta el modelo de los determinantes sociales de la salud e incluye ocho dimensiones entre las cuales se encuentra la salud ambiental {Social, 2013 #487}. En este contexto se define la salud ambiental como el conjunto de políticas que buscan favorecer la calidad de vida y salud y materializar el derecho a un ambiente sano a través del cumplimiento de cuatro objetivos: 1) Promover la salud de las poblaciones vulnerables a procesos ambientales. 2) Promover el desarrollo sostenible con tecnologías de producción limpia y consumo responsable. 3) Atender de forma prioritaria las necesidades sanitarias y ambientales. 4) Mejorar las condiciones de vida mediante prevención, vigilancia y control sanitario {Gómez, 2014 #488}. También se dividió en dos componentes entre los cuales está el de situaciones en salud relacionadas con condiciones ambientales donde se debe incluir la malaria.
... The findings were endorsed by other studies in Uganda, Ethiopia, Cameroon and Sri Lanka. The studies found an increased risk of acquiring malaria among people living around mosquito breeding sites [7,[16][17][18][19]. ...
Background and Aim: Malaria remains a major public health problem and a global threat to humanity especially in sub-Saharan Africa. In a bit to combat malaria in Cameroon, about 8million Cameroonian received the insecticide treating nets (ITNs) in 2011. However, hospital based reported prevalence of malaria still remains high. Our objective was to determine the community based prevalence and possible risk factors of malaria in pregnancy in the Mamfe health district, south west region-Cameroon. Methods: This was a community-based cross-sectional study involving 269 pregnant women in the Mamfe health district of Cameroon. Three out of the 5 health areas were randomly selected and pregnant women were later sampled by convenience and an interviewer administered questionnaire was done. Also rapid diagnostic test (RDT) for malaria was done for all the participants. Data was analysed using Epi info version 3.5.4 at a level of error of 5%. Results: Of the 269 pregnant women who took part in the study, 106 (39.6%) were positive for malaria. Risk factors associated with developing malaria among them were: presence of mosquito breeding sites (OR=0.001, 95%CI; 0.02-0.27, p-value=0.001), not sleeping under Insecticide treated nets(ITNs) (OR=0.01, 95%CI; 0.01-0.03, p-value=0.001), bushes around houses (OR=0.24, 95%CI; 0.07-0.79, p-value=0.02) and not taking intermittent preventive treatment (IPT) (OR=0.08, 95%CI; 0.01-0.49 p-value=0.01). Majority of participant knew malaria can be prevented by sleeping under ITNs 75% (95%CI; 69.9-80.5) and uptake of IPT 23.8% (95%CI; 18.8-29.2). Conclusion: Prevalence of malaria in pregnancy in the Mamfe health district is higher than reported by the regional delegation of public health for the south west. Risk factors include: mosquito breeding sites, bushes around compound, not taking IPT and none use bed nets are known to pregnant women. Interventions to fight against malaria in pregnancy should target intensification of health education on environmental hygiene and use of ITNs.
... In agreement with our results, a study in western Kenya highlands [50] and Iguhu Village, western Kenya [53], showed that houses located closer to the vector habitats had a significantly higher distribution of adult mosquitoes than those farther away. Residents near to the major vector-breeding sites were also observed to be more affected by malaria in urban Uganda [54] and Adama town, in Ethiopia [55], as compared to residents far from breeding sites. ...
Abstract
Background: Vector control interventions using long-lasting insecticidal nets (LLINs) and indoor residual spraying
(IRS) are commonly practiced tools for the control of malaria in Ethiopia. In order to evaluate the effectiveness of these
control interventions, and understand the prevailing malaria vectors, their incrimination in disease transmission, and
their resting and feeding behavior, we set out to identify the Anopheles species, their blood meal sources, and entomological
inoculation rate (EIR) in Ghibe and Darge within the Ghibe River basin, southwestern Ethiopia.
Methods: Adult Anopheles mosquitoes were sampled both indoors and outdoors from January 2015 to October
2016 using Centers for Disease Control and Prevention (CDC) light traps, pyrethrum spray catch (PSC), artificial pit
shelters and mouth aspirators. Mosquito species were morphologically identified, and their blood meal sources and
malaria sporozoite rates were assessed using enzyme-linked immunosorbent assays.
Results: In total, 13 species of Anopheles mosquitoes were identified, among which Anopheles gambiae (s.l.) was the
predominant species: 87.9 and 67.7% in Ghibe and Darge, respectively. The mean density of An. gambiae (s.l.) collected
per night using CDC light traps was 1.8 and 0.7 outdoors and indoors, respectively, in Ghibe, and 0.125 and 0.07
indoors and outdoors, respectively, in Darge. Anopheles mosquito abundance was higher in houses near the river than
in houses far from the river in both study sites. Among Anopheles mosquitoes sampled using CDC light trap catches,
67.6% were unfed and the indoor and outdoor human blood indices of An. gambiae (s.l.) were 58.4 and 15.8%, respectively
in Ghibe, while in Darge, they were 57.1 and 50%, respectively. Sporozoite rates were 0.07% for P. vivax and
0.07% for P. falciparum in Ghibe and zero in Darge. In Ghibe, the overall EIRs for P. falciparum and P. vivax were zero and
8.4 infective bites/person/year, respectively, in 2015, while zero and 5.4 infective bites/person/year for P. vivax and P.
falciparum, respectively, in 2016. No Plasmodium-positive Anopheles mosquitoes were identified from Darge.
Conclusions: Anopheles gambiae (s.l.), the principal vector of malaria in Ethiopia was the most abundant species both
indoors and outdoors, fed both on human and cattle blood and occurred at higher frequencies near rivers. Anopheles
gambiae (s.l.) that were circumsporozoite-positive for Plasmodium species were collected from Ghibe, but not Darge.
... Such risk is probably due to higher exposure, e.g. close proximity to breeding sites or an environment favoring exposure to the vector, and not to residual parasitaemia or gametocytaemia as the latter would decrease after two months [39,40]. This suggests that risk of infection and clinical disease is extremely focal as already shown in The Gambia [8], Senegal [41], and Kenya [42]. ...
Mass drug administration (MDA) may further reduce malaria transmission in low transmission areas. The impact of MDA on dynamics of malaria transmission was determined in a prospective cohort study. Annual rounds of MDA with dihydroartemisinin-piperaquine (DP) were implemented over two years (2014 and 2015) in six village pairs before the malaria transmission season. Monthly blood samples were collected from all residents between July and December for microscopy and nested PCR. The incidence and prevalence of infection and clinical disease, and the risk of malaria re-infection post-MDA were determined. Coverage of three DP doses was 68.2% (2014) and 65.6% (2015), compliance was greater than 80%. Incidence of infection was significantly lower in 2014 (IR=0.2 PPY) than in 2013 (IR=1.1 PPY) (P<0.01); monthly infection prevalence declined in the first three months post-MDA. Clinical malaria incidence was significantly lower in 2014 (IR=0.1 PPY) and 2015 (IR=0.2 PPY) than in 2013 (IR=0.4 PPY) (P<0.01) but remained higher in eastern Gambia. Individuals infected before MDA had a 2-fold higher odds of re-infection post-MDA (AOR=2.5, 95% CI: 1.5-4.3, P<0.01). MDA reduced malaria infection and clinical disease during the first months of each transmission season. The reduction was maintained in low transmission areas, but not in eastern Gambia. One MDA round could be followed by focal MDA targeting individuals found infected during the dry season. Repeated MDA rounds, some of them during the dry season over a much larger geographical area, may result in a more marked and sustained decrease of malaria transmission.
... Such risk is probably due to higher exposure, e.g. close proximity to breeding sites or an environment favoring exposure to the vector, and not to residual parasitaemia or gametocytaemia as the latter would decrease after two months [39,40]. This suggests that risk of infection and clinical disease is extremely focal as already shown in The Gambia [8], Senegal [41], and Kenya [42]. ...
Background:
Mass drug administration (MDA) may further reduce malaria transmission in low transmission areas. The impact of MDA on dynamics of malaria transmission was determined in a prospective cohort study.
Methods:
Annual rounds of MDA with dihydroartemisinin-piperaquine (DP) were implemented over two years (2014 and 2015) in six village pairs before the malaria transmission season. Monthly blood samples were collected from all residents between July and December for microscopy and nested PCR. The incidence and prevalence of infection and clinical disease, and the risk of malaria re-infection post-MDA were determined.
Results:
Coverage of three DP doses was 68.2% (2014) and 65.6% (2015), compliance was greater than 80%. Incidence of infection was significantly lower in 2014 (IR=0.2 PPY) than in 2013 (IR=1.1 PPY) (P<0.01); monthly infection prevalence declined in the first three months post-MDA. Clinical malaria incidence was significantly lower in 2014 (IR=0.1 PPY) and 2015 (IR=0.2 PPY) than in 2013 (IR=0.4 PPY) (P<0.01) but remained higher in eastern Gambia. Individuals infected before MDA had a 2-fold higher odds of re-infection post-MDA (AOR=2.5, 95% CI: 1.5-4.3, P<0.01).
Conclusions:
MDA reduced malaria infection and clinical disease during the first months of each transmission season. The reduction was maintained in low transmission areas, but not in eastern Gambia. One MDA round could be followed by focal MDA targeting individuals found infected during the dry season. Repeated MDA rounds, some of them during the dry season over a much larger geographical area, may result in a more marked and sustained decrease of malaria transmission.
... The study conducted in Eddo Kontola was indicated that, people living nearest of Lake Zway had more affected with malaria than those living far from the lake [12]. In rural setting, incidence of clinical episodes of malaria was strongly associated with proximity of residence to potential mosquito breeding sites [11,13]. ...
... The LLINs in households living more than 1 km from potential vector breeding sites were less likely to survive. This could be related to a higher perceived risk of mosquito bites and malaria infection among net owners living closer to a vector breeding site [43,44]. In this study, neither using the net the night before the survey nor having ever washed the net was associated with functional survival of LLINs. ...
Background:
Long-lasting insecticidal nets (LLINs) are a key tool for malaria prevention and control. Currently, the recommended serviceable life of an LLIN is 3 years under field conditions. However, field studies show considerable variation in LLIN lifespan, from less than 2 years to more than 4 years. This study aimed to determine the attrition, physical integrity, functional survival, and bio-efficacy of LLINs under field conditions in south-central Ethiopia.
Methods:
In October 2014, 7740 LLINs (PermaNet® 2.0) were distributed to 3006 households. Among the distributed LLINs, a cohort study involving 1532 LLINs in 659 households was carried out from October 2014 to November 2016. Data were collected every 6 months by observation, and through interviews with the heads of households. The proportional hole index was used to categorize LLINs as either serviceable or torn. In addition, 120 randomly selected LLINs were tested for bio-efficacy.
Results:
The overall attrition of LLINs was 96% (n = 993) during the study period. The nets' attrition was mainly due to disposal (64.2%; n = 638). The proportion of LLINs with a hole size 0.5 cm or larger was 79.5% after 24 months. The use of the net on the previous night and having a clean net were associated with a good physical integrity. However, living in a household more than 1 km away from the mosquitoes' breeding site was associated with poor physical integrity. By the 24th month, only 4% of the nets met the criteria for functional survival. The median functional survival time of the nets was 12 months. A longer functional survival was associated with having a clean net, and shorter survival was associated with living in a household more than 1 km away from the mosquitoes' breeding site. The PermaNet® 2.0 met the criteria of effective bio-efficacy up to month 24 after distribution.
Conclusions:
The study showed that the median serviceable life of LLINs is only 12 months. However, the bio-efficacy of the LLINs is acceptable for at least 24 months. Therefore, stronger and more efficient LLINs need to be developed for conditions similar to those studied here.
... In Africa, malaria transmission is unevenly distributed, often clustering around water bodies [15][16][17]. The association of malaria transmission with specific locations is attributable to the presence of breeding sites of the anopheline vectors, with water body characteristics playing an important role in determining the risk of malaria transmission. ...
Background
Water level management has been suggested as a potential tool to reduce malaria around large reservoirs. However, no field-based test has been conducted to assess the effect of water level management on mosquito larval abundance in African settings. The objective of the present study is to evaluate the effects of water level drawdown rates on mosquito larval abundance.
Methods
Twelve experimental dams were constructed on the foreshore of the Koka Dam in Ethiopia. These were grouped into four daily water drawdown treatments, each with three replicates: no water-level drawdown (Group 1; Control), 10 mm.d⁻¹ (Group 2), 15 mm.d⁻¹ (Group 3) and 20 mm.d⁻¹ (Group 4). Larval sampling was conducted weekly for a period of 6 weeks each in the main malaria transmission season (October to November 2013) and subsequent dry season (February to March 2014). Larval densities were compared among treatments over time using repeated measures Analysis of Variance (ANOVA).
Results
A total of 284 Anopheles mosquito larvae were collected from the experimental dams during the study period. Most (63.4%; n = 180) were collected during the main malaria transmission season while the remaining (36.6%; n = 104) were collected during the dry season. Larvae comprised four Anopheles species, dominated by Anopheles arabiensis (48.1% of total larval samples; n = 136) and An. pharoensis (33.2%; n = 94). Mean larval density was highest in control treatment dams with stable water levels throughout the study, and decreased significantly (P < 0.05) with increasing water drawdown rates in both seasons. During the main transmission season, anopheline larval density was generally lower by 30%, 70% and 84% in Groups 2, Group 3 and Group 4, respectively, compared with the control dams (Group 1). In the dry season, larval density was reduced by 45%, 70% and 84% in Groups 2, Group 3 and Group 4, respectively, when compared to the control dams.
Conclusion
Increased water drawdown rates were associated with lower mosquito larval abundance. Water level management could thus serve as a potential control measure for malaria vectors around reservoirs by regulating the persistence of shallow shoreline breeding habitats. Dam operators and water resource managers should consider incorporating water level management as a malaria control mechanism into routine dam operations to manage the risk of malaria transmission to human populations around reservoirs.
... Spatio-temporal variations in malaria burden are due to individual, household, community and environmental factors [1][2][3][4][5]. There is a need to monitor and identify spatio-temporal variations of malaria burden to inform decision-making; however, measuring these variations is complex and costly. ...
Background:
Spatio-temporal variations in malaria burden are currently complex and costly to measure, but are important for decision-making. We measured the spatio-temporal variation of clinical malaria incidence at a fine scale in a cohort of children under five in an endemic area in rural Chikhwawa, Malawi, determined associated factors, and monitored adult mosquito abundance.
Methods:
We followed-up 285 children aged 6-48 months with recorded geolocations, who were sampled in a rolling malaria indicator survey, for one year (2015-2016). Guardians were requested to take the children to a nearby health facility whenever ill, where health facility personnel were trained to record malaria test results and temperature on the child's sick-visit card; artemisinin-based combination therapy was provided if indicated. The cards were collected and replaced 2-monthly. Adult mosquitoes were collected from 2-monthly household surveys using a Suna trap. The head/thorax of adult Anopheles females were tested for presence of Plasmodium DNA. Binomial logistic regression and geospatial modelling were performed to determine predictors of and to spatially predict clinical malaria incidence, respectively.
Results:
Two hundred eighty two children, with complete results, and 267.8 child-years follow-up time were included in the analysis. The incidence rate of clinical malaria was 1.2 cases per child-year at risk; 57.1% of the children had at least one clinical malaria case during follow-up. Geographical groups of households where children experienced repeated malaria infections overlapped with high mosquito densities and high entomological inoculation rate locations.
Conclusions:
Repeated malaria infections within household groups account for the majority of cases and signify uneven distribution of malaria risk within a small geographical area.
... The study conducted in Eddo Kontola was indicated that, people living nearest of Lake Zway had more affected with malaria than those living far from the lake [12]. In rural setting, incidence of clinical episodes of malaria was strongly associated with proximity of residence to potential mosquito breeding sites [11,13]. ...
... Another factor which may be associated with altitude is suitability for mosquito breeding [33]. Living further away from a river and the forest were protective factors against malaria The relationship between malaria incidence and distance to a river and/or a forest (as potential breeding sites) has been observed before [34,35]. Bata district is a tropical zone rich in vegetation, which provides few breeding sites associated with irrigated areas on the banks of a river. ...
Abstract Background The transmission of malaria is intense in the majority of the countries of sub-Saharan Africa, particularly in those that are located along the Equatorial strip. The present study aimed to describe the current distribution of malaria prevalence among children and its environment-related factors as well as to detect malaria spatial clusters in the district of Bata, in Equatorial Guinea. Methods From June to August 2013 a representative cross-sectional survey using a multistage, stratified, cluster-selected sample was carried out of children in urban and rural areas of Bata District. All children were tested for malaria using rapid diagnostic tests (RDTs). Results were linked to each household by global position system data. Two cluster analysis methods were used: hot spot analysis using the Getis-Ord Gi statistic, and the SaTScan™ spatial statistic estimates, based on the assumption of a Poisson distribution to detect spatial clusters. In addition, univariate associations and Poisson regression model were used to explore the association between malaria prevalence at household level with different environmental factors. Results A total of 1416 children aged 2 months to 15 years living in 417 households were included in this study. Malaria prevalence by RDTs was 47.53%, being highest in the age group 6–15 years (63.24%, p
... The highest risk of malaria transmission in such settlements, common in Amazonian Brazil and Peru [7,22,56], is typically in the newest settlements where migrants have no previous exposure to Plasmodium and little effective shelter from bites of infected An. darlingi. Proximity of residences to potential mosquito breeding-sites is also associated with the likelihood of becoming infected with Plasmodium [57][58][59]. The two rural settlements of the present study, Granada and Remansinho, have experienced anthropogenic landscape modification to different degrees because of their relative ages; Granada was initiated in 1982 and Remansinho 25 years later [55,60]. ...
Background
In recent decades, throughout the Amazon Basin, landscape modification contributing to profound ecological change has proceeded at an unprecedented rate. Deforestation that accompanies human activities can significantly change aspects of anopheline biology, though this may be site-specific. Such local changes in anopheline biology could have a great impact on malaria transmission. The aim of this study was to investigate population genetics of the main malaria vector in Brazil, Anopheles darlingi, from a microgeographical perspective. Methods
Microsatellites and ddRADseq-derived single nucleotide polymorphisms (SNPs) were used to assess levels of population genetic structuring among mosquito populations from two ecologically distinctive agricultural settlements (~60 km apart) and a population from a distant (~700 km) urban setting in the western Amazon region of Brazil. ResultsSignificant microgeographical population differentiation was observed among Anopheles darlingi populations via both model- and non-model-based analysis only with the SNP dataset. Microsatellites detected moderate differentiation at the greatest distances, but were unable to differentiate populations from the two agricultural settlements. Both markers showed low polymorphism levels in the most human impacted sites. Conclusions
At a microgeographical scale, signatures of genetic heterogeneity and population divergence were evident in Anopheles darlingi, possibly related to local environmental anthropic modification. This divergence was observed only when using high coverage SNP markers.
... Malaria cannot be considered a rural disease any longer. With the growing human population in urban areas, the chances of urban transmission may be higher than rural (Staedke et al., 2003;Donnelly et al., 2005;Hay et al., 2005). One of the major aspects of sub-Saharan Africa's development which has had a significant impact on malaria transmission is urbanization (Tatem et al., 2013). ...
This book reviews the influence of climate change on urban and public pests such as mosquitoes, flies, ticks, and wood pests (such as termites), with respect to population, distribution, disease, damage and control. Consisting of 13 chapters, the book systematically addresses how the impact of climate change on pests in urban areas differs from natural areas, focusing on the increased temperatures of urban locations, the effect of natural disasters, the manner of land use and the consequences of human habitation. It highlights key information on how climate change and urban pests affect human health, discusses the effects of natural disasters such as flooding, and looks at issues which could influence the management of pests. It also explores a range of international opinions from recognized authorities covering 6 continents. Presenting up-to-date knowledge, this book is an essential resource for researchers in urban pests, entomology and public health, as well as scientists, environmentalists and policy makers involved in studies on climate change.
... (Clark, et al 2010, Keiser, et al 2004 Peak incidences occur following the two rainy seasons (March to May, and September to November), with the highest prevalences in proximity with standing water. (Clark, et al 2010, Odongo-Aginya, et al 2005, Staedke, et al 2003 Exposed residents receive 5-50 infective bites per year, and P falciparum accounts for 90-98% of all malaria infections. (Zaramba 2005(Zaramba -2010 In children admitted to Mulago Hospital, malaria accounts for 30-50% of outpatient visits, 35% of hospital admissions, and ~10% of hospital deaths. ...
... Furthermore, proximity to water bodies and to blood meals provides important environmental resources for Anophelines, as they require shallow, temporary bodies of fresh water that may contain floating and submerged algae, emergent grass, or rice to deposit their eggs [11,[33][34][35][36][37][38][39]. The proximity to water is thus considered an important factor when identifying resting habitats [40][41][42][43]. ...
Background
Knowledge of Anopheles resting habitats is needed to advance outdoor malaria vector control. This study presents a technique to map locations of resting habitats using high-resolution satellite imagery (world view 2) and probabilistic Dempster-Shafer (D-S) modelling, focused on a rural village in southern Mali, West Africa where field sampling was conducted to determine outdoor habitat preferences of Anopheles gambiae, the main vector in the study area.
Methods
A combination of supervised and manual image classification was used to derive an accurate land-cover map from the satellite image that provided classes (i.e., photosynthetically active vegetation, water bodies, wetlands, and buildings) suitable for habitat assessment. Linear fuzzy functions were applied to the different image classes to scale resting habitat covariates into a common data range (0–1) with fuzzy breakpoints parameterized experimentally through comparison with mosquito outdoor resting data. Fuzzy layers were entered into a Dempster-Shafer (D-S) weight-of-evidence model that produced pixel-based probability of resting habitat locations.
Results
The D-S model provided a highly detailed suitability map of resting locations. The results indicated a significant difference (p < 0.001) between D-S values at locations positive for An. gambiae and a set of randomly sampled points. Further, a negative binomial regression indicated that although the D-S estimates did not predict abundance (p > 0.05) subsequent analysis suggested that the D-S modelling approach may provide a reasonable estimate locations of low-to-medium An. gambiae density. These results suggest that that D-S modelling performed well in identifying presence points and specifically resting habitats.
Conclusion
The use of a D-S modelling framework for predicting the outdoor resting habitat locations provided novel information on this little-known aspect of anopheline ecology. The technique used here may be applied more broadly at different geographic scales using Google Earth, Landsat or other remotely-sensed imagery to assess the malaria vector resting habitats where outdoor control measures can reduce the burden of the disease in Africa and elsewhere.
... Urbanization, widespread use of malaria control measures and effective treatment in recent years have had a significant impact in reducing the prevalence of malaria in many African cities, as well as contributing to the more heterogeneous risk in malaria observed in many urban areas [1][2][3][4][5]. In Kinshasa, the capital of the DRC malaria has considerably decreased during the past 30 years. ...
Background
There is little data on the risk factors for malaria infection in large cities in central Africa and in all age groups. There may be different associations with the risk factors for areas with different malaria transmission intensities such as the effect of fever or age. This study aimed at identifying risk factors associated with Plasmodium infection and anaemia among children 6–59 months and individuals aged older than 5 years in Kinshasa, a large city with heterogeneity in malaria prevalence.
Methods
This study analysed data from 3342 children aged 6–59 months from 25 non-rural health zones (HZs) and for 816 individuals aged older than 5 years from two HZs in Kinshasa (non-rural), collected during a cross sectional malaria survey in 2011. Logistic regression with random effects was used to investigate predictors for malaria and anaemia. Differences in risk factors in areas with a prevalence of less than 10 and 10 % or greater were investigated.
Results
There was evidence of a different age-pattern in the two transmission settings. For children under 5 years, the highest prevalence of malaria was observed in the 48–59 months group in both transmission settings, but it increased more gently for the lower transmission HZs (p = 0.009). In a separate analysis in children over 5 years in two selected HZs, the peak prevalence was in 5–9 years old in the higher transmission setting and in 15–19 years old in the lower transmission setting. Reported fever was associated with malaria in both transmission strata, with no evidence of a difference in these associations (p = 0.71); however in children older than 5 years there was a significant interaction with a stronger association in the low transmission HZ. Insecticide-treated net (ITN) use was associated with a lower risk of malaria infection in children 6–59 months in the high transmission HZs. Similar estimates were found in children over 5 years and the lower transmission HZ but the associations there were not significant. There was no evidence of a difference in these associations by strata. The risk of anaemia decreased with increasing age in all strata, whereas it increased with malaria infection and reported fever. ITN use did not show evidence of protection against anaemia. Low socio-economic status was associated with malaria in high transmission setting in children 6–59 months and anaemia in low transmission setting.
Conclusions
This study shows that in areas of low transmission in Kinshasa, the peak prevalence occurs in older age groups however ITN use was highest in children under 5 years. Targeted distribution of ITN to all age groups should be continued. For most risk factors, there was no evidence of an interaction with transmission intensity however the associations with age and with fever in the last 2 weeks did vary significantly.
... These results are not surprising as the existing literature on the transmission patterns of P. falciparum indicate that regions closest to mosquito breeding grounds experience the highest levels of malaria transmission (Ghebreyesus et al., 1999;(Thomas & Lindsay, 2000;Staedke et al., 2003;van der Hoek et al., 2003;Midega et al., 2012). This is because of high mosquito abundance around breeding sites such that individuals residing in the vicinity of these areas experience the highest mosquito bites accompanied by parasite inoculations. ...
The way malaria parasites are transmitted in space will have an influence on their
genetic relationships. It can be expected that parasites collected within close
geographic distances of each other would be more closely related than those across
large geographic distances. Further to this, because malaria transmission is focal and
heterogeneous in space, then the genetic relatedness between malaria parasites in
these foci of malaria transmission would be greater within tightly clustered regions.
Thus, using the level of genetic relatedness of these parasites would reveal how they
are transmitted not only within these foci but at different geographic settings. This
knowledge would offer insight on how malaria control methods can be effectively
disseminated.
In field settings malaria infections are polyclonal and each of the clones represented
within these infections occur at different proportions. With the aid of genetic
markers such as single nucleotide polymorphisms (SNPs) or microsatellites, parasite
clonal genotypes can be identified. In this study, the genetic markers of choice are
SNPs. Using a method that can quantify these SNPs representing the different clones
occurring at different proportions in an isolate, then each of the clonal genotypes can
be determined. Microsatellites were also used as additional markers in the study.
In this thesis, 1.Genetic markers (SNPs) across the P. falciparum genome were
identified (Chapter 3); 2. PyrosequencingTM was validated as a technique that would
enable the identification of each genetically distinct clone represented in an infection
by assigning proportions to the SNPs representing each genetically distinct clone and
enabling the identification of parasite clonal genotypes in every isolate analysed.
This was validated using laboratory prepared clone mixtures of P. falciparum. In
addition; the progeny from a cross derived from genetically characterised 3D7 and
HB3 isolates was analysed in preparation for the analysis of the field isolates
(Chapter 4). , 4. In Chapter 5, field isolates were tested and clonal genotypes
identified using both SNPs and microsatellites. A detailed population genetic
analysis was also performed and finally in Chapter 6, evidence for correlation
between the genetic relationships of these parasites and geographic distance was
investigated.
The results from field isolates summarised in this thesis were from analysis of 54
isolates; 7 samples collected from Cameroon, 13 from Kenya and 34 from Mali. The
data consists of 13 SNPs analysed by PyrosequencingTM and 8 microsatellites. 84
clonal genotypes were identified by both genetic markers from the analysed isolates. Analysis of both SNPs and microsatellites revealed that microsatellites were more
informative than the SNPs based on the observed allelic richness and heterozygosity
(genetic diversity) across all loci analysed. The overall FST value was 0.061 using
SNPs and 0.043 by microsatellites analysis. These values were low but consistent
with what is typically observed in African P falciparum populations.
Finally, analyses of the combined data set revealed that no statistically significant
levels of spatial autocorrelation existed within the studied parasite populations.
However, there was evidence of within host mixed parasite infections exhibiting a
high level of genetic relatedness compared to between host infecting clones.
... Arditi [75], argues that the rates of (successful predation) contact between a predator and a prey is most properly a function of the ratios of their proportions. This would fit into malaria mosquito which inhabit homesteads and other areas where human hosts are available, like farms and urban areas [133]. It is also clear that this contact rate does not increase without bound, as the predator -prey ratio increases, this is because once a mosquito is fed, it rests before ovipositing, to resume host seeking and biting again [106]. ...
The objective of this thesis is to model highland malaria in Western Kenya using dynamical systems. Two mathematical models are formumated, one, on differentiated susceptibility and differentiated infectivity in a metapopulation setting, two, a saturated vector feeding rate model with disease induced deaths and varying host and vector populations. In the first model, we consider the different ecosystems identified as malaria hotspots in the Western Kenya highlands and consider the ecosystems as different patches. The population in each patch is classified as, either, child (age 0-5 years), or, adult (over ( years of age). Our results are compared with some published results
... When tadpoles and invertebrate larvae started their development simultaneously they competed strongly, but symmetrical. Former studies have shown that, malaria transmission is usually higher in rural than in urban areas (STAEDKE et al 2003). There it is also more likely to find mosquitoes larvae cooccurring with tadpoles in temporary ponds (MATTHYS et al. 2006 3 Dimension and first evaluation of the use and trade of amphibians in West Africa ...
Amphibien sind global von einem Artenrückgang betroffen, wobei Ausbeutung bestimmter Froscharten einer der Gründe hierfür ist. Die vorliegende Arbeit gibt erstmals Einblick in Form, Umfang und Auswirkungen der extensiven Nutzung von Fröschen in Westafrika. Interviews mit Konsumenten und in den Froschhandel Involvierten ermöglichten die Nutzung und den Handel von Fröschen in Burkina Faso, Benin und Nigeria zu quantifizieren und zu bewerten. Während der Froschhandel in Burkina Faso eher auf lokaler Ebene abläuft, ließ sich im Norden Benins und in Nigeria ein intensiver grenzüberschreitender Handel nachweisen. Um einen möglichen anthropogenen Einfluss auf natürliche Amphibien Gemeinschaften zu ermitteln wurden natürliche Gewässer untersucht. Auf Kaulquappenebene wurden Artenverluste und die sich daraus ergebenen Konsequenzen studiert. Temporäre Savannengewässer wurden in zwei Untersuchungsgebieten in Burkina Faso untersucht, wobei die Gewässer jeweils in Gebieten mit unterschiedlichem Störungsgrad lagen: in Dörfern mit Froschfang, gegenüber in geschützten Gebieten mit Froschfangverbot. Generell konnte in den anthropogen gestörten Gebieten ein niedrigerer Artenreichtum mit gleichzeitig veränderter Zusammensetzung der Artengemeinschaften konstatiert werden. Für diese Unterschiede waren primär anthropogen veränderte Habitatfaktoren verantwortlich. Aber auch das Froschfangen kann Grund für veränderte Kaulquappengemeinschaften sein. Um Voraussagen für mögliche resultierende Konsequenzen treffen zu können ist es wichtig die ökologische Rolle betroffener Arten im System zu kennen. In künstlichen Gewässern wurde die trophische Position von vier Kaulquappenarten mit jeweils unterschiedlicher Nahrungsstrategie und die Konsequenzen ihres Verlustes für die restlichen Kaulquappen und bestimmter Ökosystemfaktoren, wie Moskitolarven, ermittelt. Die vier Kaulquappenarten unterschieden sich in ihrer trophischen Position. Zudem konnten komplexe Interaktionen zwischen den vier Fokusarten aufgedeckt werden, wobei die trophische Position je nach Gemeinschaft wechseln konnte. So konnte ich mit meiner Arbeit zeigen, dass der Verlust nur einer Art essentielle Konsequenzen für Amphibien Gemeinschaften und ökosystemische Prozesse haben kann. Chapter 1 Summary II I
... funestus. To predict the anopheline distribution at the regional scale, it is usual to take into consideration the distance between breeding sites and habitations in urban areas (Trape, 1992;Salem, 1994) as well as in rural areas (Beck, 1994, Fontenille, 1997Thomas, 2000;Hii, 1997) At village scale, in Kenya (Minakawa, 2002) and in Uganda (Staedke, 2003) distance from a house to its nearest larval habitats showed a significant correlation with anopheline densities. Our study did not demonstrate the relevance of this variable, maybe because Dielmo is a very limited space; every hut is < 300 m from the stream. ...
... Arditi [9], argues that the rates of (successful predation) contact between a predator and a prey is most properly a function of the ratios of their proportions. This would fit into malaria mosquitoes which inhabit homesteads and other areas where human hosts are available, like farms and urban areas [10]. It is also clear that this contact rate does not increase without bound, as the predator-prey ratio increases, this is because once a mosquito is fed, it rests before ovipositing, to resume host seeking and biting again [11]. ...
... Understanding the relationship between host choice and aquatic habitat choice is also important for ecological and epidemiological reasons (Reiter 2007). Bloodfeeding causes transmission of pathogens to vertebrate hosts, and oviposition site location is strongly correlated with where transmission occurs (Staedke et al. 2003, Le Menach et al. 2005 because newly emerged and recently ovipositing adult female mosquitoes begin their bloodmeal host search at an oviposition site. ...
In modeling resource choice, resources are commonly categorized as essential, complementary, or substitutable. Most models concerning nonsubstitutable resources have represented each resource as a set of identical options. In reality, nonsubstitutable resources often vary in quality. Biting insects require a bloodmeal host and an oviposition site for reproduction, and expected offspring yield from different hosts and sites varies dramatically. Because both of these resources are necessary, selection may exist for interdependent choice, or bloodfeeding decisions that depend on egglaying site distribution, and vice versa. For example, insects may be selected to feed on hosts near high-quality sites or to lay eggs in sites near high-quality hosts. These decisions may be influenced by resource distribution; some areas may have clusters of high-quality hosts or sites, but the co-occurrence of both resources may be uncommon. In this study, we demonstrate the selective advantage of interdependent choice in heterogeneous environments. A 2-patch model demonstrates that interdependent choice is advantageous when resource quality varies greatly, as threshold acceptable bloodmeal host quality differed most from in a completely random environment when oviposition site quality was highly variable, and with high movement costs. A dynamic state variable model extended this result, demonstrating that spatial correlation in quality between resources is sufficient to select for interdependent choice, and autocorrelation increases the effect of between-resource correlation on behavior. This model also demonstrates that the relationship between the resources influences optimal behavior; highly complementary resources are more likely to select for populations that exhibit interdependent choice.
... One often neglected outcome of such urban expansion is heightened disease risk as human populations encroach closer to natural mosquito breeding habitats. For example, an increased risk of malaria in Africa (Staedke et al. 2003, Midega et al. 2012 and Asia (Haque et al. 2009) has been demonstrated with decreasing distance to mosquito breeding habitats; living in a residence located within 100 meters from one or more tree hole breeding sites was demonstrated to be associated with almost four times greater risk of La Crosse encephalitis infection in eastern Ten-nessee (Erwin et al. 2002); and areas in southeast Queensland with a greater proportion of wetlands and native vegetation and levels of adult mosquito activity have been associated with higher rates of Ross River virus (RRV; Togaviridae: Alphavirus) (Muhar et al. 2000, Ryan et al. 2006, Hu et al. 2010. These studies exemplify the risks associated with living in proximity to sources of vector populations. ...
It is intuitive that vector-borne disease exposure risk is related to proximity to sources of vector breeding, but this aspect rarely receives empirical testing. The population of Western Australia (WA) is increasing rapidly, with many new residential developments proposed in close proximity to mosquito breeding habitat. However, potential mosquito-borne disease risks for future residents are given little consideration by planning authorities. The Peel region is one of the fastest growing regions in WA and regularly experiences a large number of cases of the mosquito-borne Ross River virus (RRV) disease with epidemics occuring in the region every few years. A spatial analysis of RRV disease data in the Peel region was undertaken to determine the risk associated with proximity to a mosquito breeding habitat. Geographic Information Systems (GIS) software was used to create buffers between 1 and 6 km from the breeding habitat. The number of cases per 1000 dwellings in each buffer was calculated between 2002/03 to 2011/12 for years with >100 cases across all buffers (n=5) in addition to the cumulative rate over the entire period in each buffer. Residents living within 1 km of a mosquito breeding habitat had a significantly higher rate of RRV disease compared to the background rate across the Peel region in all individual years investigated. The cumulative data over the 10-year study period showed that residents in the 1- and 2-km buffers had a significantly higher rate, whereas those living between 3 and 6 km away did not. This study demonstrates an increased mosquito-borne disease risk associated with living in close proximity to a mosquito breeding habitat in a rapidly expanding region of WA and highlights the importance of considering mosquito-borne disease risks when planning authorities assess new residential development applications. Known mosquito breeding wetlands should be incorporated into land use planning scheme maps to ensure that they are accurately delineated and the implications are considered when planning decisions are made.
... Mosquitoes have been found to breed successfully in ponds, flood plains, and irrigated fields, as they constitute stagnant waters (Keiser et al. 2005;Peterson et al. 2009). If present, natural wetlands such as swamps and streams also increase the risk of disease (Matthys et al. 2006;Staedke et al. 2003). ...
In African growing cities, vector-borne diseases (such as malaria and dengue) contribute to a large burden of childhood morbidity and mortality. During the peak of transmission, environmental factors can have an influence on those fevers, apart from the individual and household characteristics. A household survey conducted in 2008 in Dakar was completed by a community questionnaire on environmental threats that could be factored into multilevel analyses. Using a randomized sample of 7,300 children from 3,000 households dispatched within 50 neighborhoods, a three-level modeling process is presented. Rates of recent fever varied substantially from one neighborhood to another, ranging between 10 and 37 %. Findings indicate that the onset of fever is influenced by factors from all three hierarchical levels, with neighborhood factors playing a relatively lower role than the other two. Among the environmental factors, the effect of environmental sanitation is particularly interesting.
... These findings were the same as reported by Snow et al. in Peru and Staedke et al. in Uganda. 11,12 Poor ceiling design actually provides access for mosquitoes to enter respondent's house and bite the occupants. Small sample size among those live in palm thatched house could have resulted in insignificant findings for house structure. ...
The incidence of malaria in Sarawak is among the highest in Malaysia despite its downward trend since 2002. This study was conducted to identify the dominant risk factors related to malaria infection. A case-control study was conducted in Lundu District, Sarawak. Cases were 96 indigenous malaria cases registered from January to September 2005 at Lundu District Health Office. Controls were selected among those who never contracted malaria originating from the same villages as cases. Cases and control were similarly distributed with respect to age, number of household and total household income per month. Cases were more likely than controls to report high risk occupation, opened eaves, ever had movement for those aged 50 years or over and car ownership. Older age, male, lower socioeconomic level and perception of fatality toward malaria increased risk to malaria infection. Male than female had seven-fold risk to be malaria infected [adjusted odds ratio (ORa) = 7.09; 95% confidence interval (CI) = 3.21-15.65]. In term of perception of fatality toward malaria, those who did not have than did have perception of fatality toward malaria had six-fold risk to be malaria infected (ORa = 6.38; 95% CI = 1.32-30.87). On contrary, those who had lower than middle and high per capita income per month had 85% lowered risk to be malaria infected (ORa = 0.15; 95% CI = 0.03-0.72). Male, older age, lower education and socioeconomy level, lower perception towards malaria, or lower environment sanitation had increased risk to be malaria infected. (Med J Indones 2007; 16:267-71)Keywords: malaria, gender, sosioeconomics, perception, protective personal measure, environmental
This chapter explores how health affected and conditioned the development of the urban model and the building regulations of the Canal Zone, which also played an essential role in the environmental impact of permanent villages. The relationship between sanitary measures and urban regulations is studied to understand their interplay. The analysis focuses mainly on determining how the ecology and behavior of mosquitoes that cause malaria and yellow fever broadly defined the development of such building regulations. The chapter also highlights how sanitary measures shaped the urban landscape and the environment of the Canal Zone villages, using Fort Clayton as a case study.
The aftermath of extreme flood events can be particularly devastating for residential communities in proximity to flood-prone petrochemical facilities, as they are likely to experience multiple impacts from a single flood event. Hazard impacts could be from flood inundation to their properties, and floodwaters carrying contaminants from nearby facilities into their homes. While property acquisition or buyouts have been effectively used as a flood mitigation strategy, current buyout selection processes only factor in flood exposure, thereby ignoring other hazards such as exposure of properties to potential chemical substance transfer. In this paper, we identify properties that are eligible for flood buyouts but are also at a high risk of contaminant transferal during extreme flood events. We apply a benefit–cost analysis methodology to assess the economic viability of buyouts and proximity metrics to prioritize buyouts of contaminant-prone properties in Galena Park, Texas. Results indicate that, in selected flood-only property acquisition scenarios, cumulative avoided flood losses exceed the cost of property acquisition. However, although with lower cost-benefit values, a selection criterion that factors a combination of flood and contaminant-prone properties as buyouts results in multiple properties being removed from harm’s way. Our findings emphasize the potential economic benefits of applying a multi-hazard selection criterion in dealing with flood property buyouts, especially in socially vulnerable communities with high exposure to both flooding and contaminant transfer.
I examine the ability of donors to target the highest exposure to malaria risk when the health information structure is fragmented. I exploit local variations in the risk of malaria transmission induced by mining activities in the Democratic Republic of Congo as well as financial and epidemiological data from health facilities to estimate how local aid is matching the local malaria burden. Using fine‐grained data on mines and health infrastructure in a regression discontinuity design, I find no evidence that local populations exposed to the highest risk of malaria transmission receive a proportionately higher share of aid compared to neighbouring areas with reduced exposure to malaria risk.
Sub-Saharan African (SSA) cities are some of the most rapid-growing regions in the world. As estimated by the United Nations, more than 50% of the African population will reside in cities by 2030 while in absolute numbers, its population will have doubled - from 1.2 billion in 2015 to 2.5 billion by 2050. This ongoing shift has dramatically affected the capacity of several SSA cities to provide essential services for its residents, such as durable housing, employment and healthcare accessibility. On the contrary, the proliferation of slums, further marginalizing the urban poor has been an undisputed observation of the last years. It is therefore profound, that efforts to improve the quality of life of urban dwellers are needed. A starting point to do so, is to provide relevant authorities, stakeholders and organizations with useful socioeconomic, demographic and health indicators of the urban dwellers. Nonetheless, In large parts of SSA, this type of critical information is at best scarce and at worst
non-existent and certainly not suited for sophisticated intra-urban analyses. This thesis harnesses the strength of very-high-resolution (VHR) satellite remote sensing to provide multi-level (physical, socio-economic, demographic and epidemiological) representations of the urban surface in several major SSA cities. First, cutting
edge advances relevant to the classification of urban land cover are presented. Afterwards, an assessment and evaluation of the potential of VHR satellite imagery as input to population estimation, household wealth and malaria risk models at unprecedented resolutions is investigated. The conclusions of this work encourage the systematic exploitation of VHR data to support evidence-based decision making
shaping the sustainable future of SSA cities.
Hotspots constitute the major reservoir for residual malaria transmission, with higher malaria incidence than neighbouring areas, and therefore, have the potential to form the cornerstone for successful intervention strategies. Detection of malaria hotspots is hampered by their heterogenous spatial distribution, and the laborious nature and low sensitivity of the current methods used to assess transmission intensity. We adopt ecological theory underlying foraging in herbivorous insects to vector mosquito host seeking and modelling of fine-scale landscape features at the village level. The overall effect of environmental variables on the density of indoor mosquitoes, sporozoite infected mosquitoes, and malaria incidence, was determined using generalized linear models. Spatial analyses were used to identify hotspots for malaria incidence, as well as malaria vector density and associated sporozoite prevalence. We identify household occupancy and location as the main predictors of vector density, entomological inoculation rate and malaria incidence. We propose that the use of conventional vector control and malaria interventions, integrated with their intensified application targeting predicted hotspots, can be used to reduce malaria incidence in endemic and residual malaria settings.
Malaria remains a rising cause of morbidity and mortality, posing a public health problem to the world, especially Nigeria. In most malaria endemic areas, including Nigeria, pregnant women and children under age five are groups mostly at risk for the severe case of the disease. As a result of absence of any particular recommendable vaccine for malaria prevention and control, as well as the continuous records of malaria parasite resistance to drugs, the effective control of malaria has been narrowed to practice of three strategies; use of Insecticide Treated Nets (ITNs), Intermittent Preventive Treatment (IPT) and Indoor Residual Spray (IRS). This paper reviewed the barriers associated with malaria preventive strategies in Nigeria. To better understand the low adoption of these interventions by Nigerians, the Health Belief Model (HBM) was used to provide the fulcrum for the behavioural tendencies leading to decision-making of the people. Results from this review, revealed that socioeconomic status, religion, lack of awareness, and lack of community involvement in the formulation of policies on malaria interventions, among others serve as major barriers. Measure such as the need to introduce communication programmes on malaria interventions in communities to reach the entire populace rather than seeking to change individual behaviour should be encouraged.
Climate change and its accompanying sea-level rise is set to create risks to the United States’ stockpile of spent nuclear fuel, which results largely from nuclear power. Coastal spent fuel management facilities are vulnerable to unanticipated environmental events, as evidenced by the 2011 tsunami-related flooding at the Fukushima plant in Japan. We examine how policy-makers can manage climate risks posed to the coastal storage of radioactive materials, and identify the coastal spent fuel storage sites that will be most vulnerable to sea-level rise. A geospatial analysis of coastal sites shows that with six feet of sea-level rise, seven spent fuel sites will be juxtaposed by seawater. Of those, three will be near or completely surrounded by water, and should be considered a priority for mitigation: Humboldt Bay (California), Turkey Point (Florida), and Crystal River (Florida). To ensure policy-makers manage such climate risks, a risk management approach is proposed. Further, we recommend that policy-makers 1) transfer overdue spent fuel from cooling pools to dry casks, particularly where located in high risk sites; 2) develop a long-term and comprehensive storage plan that is less vulnerable to climate change; and 3) encourage international nuclear treaties and standards to take climate change into account.
In this paper, we propose a delayed mathematical model to break the life cycle of anopheles mosquito at the larva stage by incorporating a time delay τ at the larva stage that accounts for the period of growth or development to pupa. We prove local stability of the system’s equilibrium and find the critical values for Hopf bifurcation to occur. Also, we find that the system’s equilibrium undergoes stability switching from stable to periodic to unstable and vice versa when the time delay τ crosses the imaginary axis from the left half plane to the right half plane in the (Re,Im) plane. Finally, we perform some numerical simulations and the results agree well with the analytical analysis. This is the first time such a model is proposed.
One of the specificity of African sub-Saharan countries like Benin lies in their sub-tropical climate, warm and humid. Those climatic characteristics allow the existence of an endemic malaria transmission. However, at a micro-scale, different people are not exposed similarly to this health risk. Therefore, we wanted to understand which environmental characteristics (in a broad sense) were determinant for the malaria transmission at this very fine scale. We conducted a study in a rural district of southern Benin, Tori-Bossito, composed of nine villages. A territorial diagnosis, combined with an epidemiological survey of a cohort of 600 new-born, and with catches of anopheles vectors during the 3 years of the study (2007-2010), allowed the identification of i) the areas were the vectors was predominant, and ii) the vulnerability factors of people. The fieldwork consisted in collecting multi-scale environmental indicators (regional and local), and conducting a human geography analysis concerning bed nets and insecticides utilization practices, structure of habitat, and soil occupation close to the life places. By modeling these environmental variables into a GIS (Geographic Information System), we were able to show that a "territorialisation" of the risk in Tori-Bossito was present, associated with ethnic and socio-economic conditions. A spatial segregation linked to life-conditions that questions the vulnerability of people in a context of rural-urban migrations.
The dispersion of anopheline mosquitoes from their breeding places and its impact on malaria epidemiology has been investigated in Dakar, Senegal, where malaria is hypoendemic and almost exclusively transmitted by Anopheles arabiensis. Pyrethrum spray collections were carried out along a 910-meter area starting from a district bordering on a permanent marsh and continuing into the center of the city. According to the distance from the marsh, vector density (the number of An. arabiensis per 100 rooms) at 0-160, 160-285, 285-410, 410-535, 535-660, 660-785, and 785-910 meters was 84, 40, 5, 2, 2, 0.4, and 0, respectively, during the dry season, and 414, 229, 110, 84, 99, 69, and 21, respectively, during the rainy season. The proportion of 8-11-year-old children with negative immunofluorescent antibody test results for Plasmodium falciparum was 17%, 28%, 44%, 54%, 50%, 63%, and 73%, respectively, in these different sections. Malaria prevalence in the community was maximum in the area bordering on the marsh where it ranged from 1% to 15% (average 6%) according to age and season of the year. These findings show the epidemiologic importance of vector density gradients in Dakar. The implications for malaria control in urban areas are discussed.
To measure morbidity due to malaria and to study its relationship with transmission and parasitemia in children living in an area of low malaria endemicity, a cohort study of 343 schoolchildren was undertaken during a one-year period in Dakar, Senegal. From parallel investigations on transmission and the frequency of malaria as a cause for outpatient visits, three different seasons were chosen for close monitoring of different clinical parasitologic, and sero-immunologic parameters. The daily incidence rates of malaria parasitemia and primary attacks were at a maximum level during the high transmission season (0.00198 and 0.00185 new cases/person/day, respectively) and decreased considerably during the season of low transmission. For each given period, the values of these two rates were close to each other, suggesting that each new infection was followed by a clinical attack. During the period of maximum transmission, clinical malaria prevalence was 1.36% and malaria was responsible for 36% of school absences due to medical reasons. At the end of the period of minimum transmission, clinical malaria prevalence was 0.15% and malaria was responsible for 3% of school absences due to medical reasons. In contrast, parasite prevalence hardly varied with the season (minimum 3.6%, maximum 7.5%). In a one-year period, the total number of new malarial infections was estimated between 173 and 230. Because of the existence of a vector density gradient in the area concerned, the annual malaria incidence varied considerably according to the children's place of residence.(ABSTRACT TRUNCATED AT 250 WORDS)
Malaria transmission is strongly associated with location. This association has two main features. First, the disease is focused around specific mosquito breeding sites and can normally be transmitted only within certain distances from them: in Africa these are typically between a few hundred metres and a kilometre and rarely exceed 2-3 kilometres. Second, there is a marked clustering of persons with malaria parasites and clinical symptoms at particular sites, usually households. In localities of low endemicity the level of malaria risk or case incidence may vary widely between households because the specific characteristics of houses and their locations affect contact between humans and vectors. Where endemicity is high, differences in human/vector contact rates between different households may have less effect on malaria case incidences. This is because superinfection and exposure-acquired immunity blur the proportional relationship between inoculation rates and case incidences. Accurate information on the distribution of malaria on the ground permits interventions to be targeted towards the foci of transmission and the locations and households of high malaria risk within them. Such targeting greatly increases the effectiveness of control measures. On the other hand, the inadvertent exclusion of these locations causes potentially effective control measures to fail. The computerized mapping and management of location data in geographical information systems should greatly assist the targeting of interventions against malaria at the focal and household levels, leading to improved effectiveness and cost-effectiveness of control.
The burden of malaria is increasing, especially in sub-Saharan Africa, because of drug and insecticide resistance and social and environmental changes. Thus, there is an urgent need for vaccines, new drugs and insecticides. Parasite, mosquito and human genome projects are helping in the search for new control tools and international donors are developing new funding mechanisms that could make them available to poor countries. But these new tools will achieve their maximum impact only if additional resources are deployed to strengthen malaria research and control communities in countries where the new tools will be used.
Malaria draws global attention in a cyclic manner, with interest and associated financing waxing and waning according to political and humanitarian concerns. Currently we are on an upswing, which should be carefully developed. Malaria parasites have been eliminated from Europe and North America through the use of residual insecticides and manipulation of environmental and ecological characteristics; however, in many tropical and some temperate areas the incidence of disease is increasing dramatically. Much of this increase results from a breakdown of effective control methods developed and implemented in the 1960s, but it has also occurred because of a lack of trained scientists and control specialists who live and work in the areas of endemic infection. Add to this the widespread resistance to the most effective antimalarial drug, chloroquine, developing resistance to other first-line drugs such as sulfadoxine-pyrimethamine, and resistance of certain vector species of mosquito to some of the previously effective insecticides and we have a crisis situation. Vaccine research has proceeded for over 30 years, but as yet there is no effective product, although research continues in many promising areas. A global strategy for malaria control has been accepted, but there are critics who suggest that the single strategy cannot confront the wide range of conditions in which malaria exists and that reliance on chemotherapy without proper control of drug usage and diagnosis will select for drug resistant parasites, thus exacerbating the problem. An integrated approach to control using vector control strategies based on the biology of the mosquito, the epidemiology of the parasite, and human behavior patterns is needed to prevent continued upsurge in malaria in the endemic areas.
The rapid increase in the world's urban population has major implications for the epidemiology of malaria. A review of malaria transmission in sub-Saharan African cities shows the strong likelihood of transmission occurring within these sprawling cities, whatever the size or characteristics of their bioecologic environment. A meta-analysis of results from studies of malaria transmission in sub-Saharan Africa shows a loose linear negative relationship between mean annual entomologic inoculation rates (EIR) and the level of urbanicity. Few studies have failed to find entomologic evidence of some transmission. Our results show mean annual EIRs of 7.1 in the city centers, 45.8 in periurban areas, and 167.7 in rural areas. The impact of urbanization in reducing transmission is more marked in areas where the mean rainfall is low and seasonal. Considerable variation in the level of transmission exists among cities and within different districts in the same city. This article presents evidence from past literature to build a conceptual framework to begin to explain this heterogeneity. The potential for malaria epidemics owing to decreasing levels of natural immunity may be offset by negative impacts of urbanization on the larval ecology of anopheline mosquitoes. Malaria control in urban environments may be simpler as a result of urbanization; however, much of what we know about malaria transmission in rural environments might not hold in the urban context.
A temporal and spatial study of malaria transmission in a suburban area of Maputo, Mozambique with a mean population density of 2,737/km2 was made from December 1992 to June 1995. A steep but continuous gradient was observed in the Plasmodium falciparum prevalence from 59.0% adjacent to the breeding sites to 5.4% only a few hundred meters distant. The entomologic inoculation rate ranged from a number too low to be determined in some districts to 20 infectious bites per person per year in the others. The risk of malaria was 6.2 times higher for individuals living less than 200 meters from the breeding sites than for individuals living 500 meters or more away from the breeding sites. In areas of high human density, mosquito and parasite dispersion is very limited, and therefore malaria control strategies could be more specifically targeted.
We investigated local-scale variation in malaria transmission and infection in children within a continuous landscape by retrospective
spatial analysis of entomological and clinical data collected during 1988 and 1989 in The Gambia, West Africa. Parasite prevalence
was negatively correlated with vector abundance and exposure to malaria parasites in 10 villages where entomological surveillance
had been carried out. Variation in bednet use did not explain this finding. Mosquito-breeding habitat was retrospectively
mapped using 20-m spatial resolution multispectral SPOT satellite imagery from 1988. From these data we estimated by linear
regression the risk of exposure to malaria parasites in 26 villages where clinical surveys of children had been made. As exposure
increased, so did parasite prevalence; but at higher levels of exposure, parasite prevalence declined. Our findings demonstrate
marked differences in exposure to malaria in villages over distances of less than 2 km from mosquito breeding sites and suggest
that there are also large differences in immunity between neighbouring settlements.
The causes of local variation in the prevalence of malaria were investigated in rural Gambia. Cross-sectional prevalence surveys were carried out among 1184 young children (aged 6 months-5 years) in 48 villages, at the end of the transmission season in 1996. Villages were categorized according to distance from the nearest vector breeding sites, and the patterns of malaria transmission, infection and disease compared. Children living in villages within 3 km of breeding sites experienced more infective bites, and higher prevalences of parasitaemia and spleen enlargement than less-exposed children living further away. Clinical illness, in contrast, was more common among infected children who were less exposed. Infected children living 3 km or more from breeding sites were more likely to have high-density parasitaemia (odds ratio [OR] = 1.98), fever (OR = 2.60) and high-density parasitaemia together with fever (OR = 3.17). Clinical attacks did not decline in older children, as seen amongst children who were more exposed. These findings show that significant differences in the risk of infection and clinical attacks can occur over very short distances. The age at which protective immunity is acquired may be delayed in villages where transmission intensity is lower, thus increasing the risk of a clinical attack following infection. Communities with the lowest vector densities may be those at greatest risk of disease.
New antimalarial treatments are urgently needed in sub-Saharan Africa. Improved therapies should decrease failure rates in the short term, but their effect on incidence of subsequent episodes of malaria is little studied. We aimed to compare the short-term and long-term effectiveness of three antimalarial regimens in children from Kampala, Uganda.
We randomly allocated healthy children aged 6 months to 5 years to receive 25 mg/kg sulfadoxine and 1.25 mg/kg pyrimethamine plus either placebo, 25 mg/kg amodiaquine, or 12 mg/kg artesunate. Participants were followed up for 1 year and received the same preassigned treatment for every new episode of uncomplicated malaria diagnosed during follow-up. Recrudescent and new infections were distinguished by comparison of polymorphisms in merozoite surface protein 2 (MSP2). Our primary endpoint was the total number of treatments for malaria per time at risk. Analyses were done per protocol.
183 (61%) of 316 participants were diagnosed with at least one episode of uncomplicated malaria. A total of 577 episodes of uncomplicated Plasmodium falciparum malaria were treated with study drugs; all regimens were safe and well tolerated. Clinical treatment failure after 14 days was significantly more frequent in the sulfadoxine/pyrimethamine group (38 of 215, 18%) compared with either the sulfadoxine/pyrimethamine plus amodiaquine group (two of 164, 1%; p<0.0001) or sulfadoxine/pyrimethamine plus artesunate group (one of 198, 1%; p<0.0001). After 28 and 42 days, patients in the sulfadoxine/pyrimethamine plus amodiaquine group were significantly less likely to develop malaria than were those in the other groups. Overall, sulfadoxine/pyrimethamine plus amodiaquine reduced the rate of subsequent treatments for malaria by 54% (95% CI 36-66, p<0.0001) compared with sulfadoxine/ pyrimethamine alone and by 37% (12-54, p=0.007) compared with sulfadoxine/pyrimethamine plus artesunate.
Sulfadoxine/pyrimethamine plus amodiaquine could be used as an inexpensive regimen to decrease the rate of subsequent episodes of malaria.
To assess malaria-related knowledge, attitude and practices (KAP) among primary caregivers, to identify associations between primary caregivers' characteristics and positive KAP towards malaria, and to identify independent predictors of childhood malaria incidence in an urban setting.
Children aged 6 months to 5 years living in Kampala, Uganda were enrolled as part of a longitudinal study on antimalarial therapy. Primary caregivers of 307 children were interviewed and information was collected on demographics, malaria-related KAP, environmental and household factors. Malaria incidence was measured prospectively using passive surveillance.
A total of 90% of respondents reported mosquitoes and/or malaria as the cause of fever. Caregivers reported that if their child had fever, 63% would go to a clinic or hospital as their first action and 97% as their first or second action. Only 38% knew that chloroquine was the recommended first-line treatment for malaria and 29% knew the correct dose. Preventive measures for malaria were reported in 45% of households but only 25% reported using bednets. Higher levels of education for the caregiver were associated with positive malaria-related KAP. Malaria incidence varied widely. The following were independent predictors of malaria incidence: (1). Children aged 24-41 months at enrolment had a higher incidence of malaria. (2). Reported bednet or chemoprophylaxis use reduced the incidence of malaria. (3). A child's place of residence was associated with incidence. (4). Children from households using open water sources had a higher incidence than those using closed sources.
Primary caregivers were knowledgeable about malaria and used modern health care facilities but knew less about the proper administration of antimalarials and had limited use of preventive measures. Malaria incidence was associated with child's age at enrolment, geography, source of water and the use of preventive measures.