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Delenasaw Yewhalaw,
Fantahun Wassie,
Walter Steurbaut,
Pieter Spanoghe, Wim Van Bortel,
Leen Denis,
Dejene A Tessema,
Yehenew Getachew,
Marc Coosemans,
Luc Duchateau,
Niko Speybroeck
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ABSTRACT: Long-lasting insecticidal hammocks (LLIHs) are being evaluated as an additional malaria prevention tool in settings where standard control strategies have a limited impact. This is the case among the Ra-glai ethnic minority communities of Ninh Thuan, one of the forested and mountainous provinces of Central Vietnam where malaria morbidity persist due to the sylvatic nature of the main malaria vector An. dirus and the dependence of the population on the forest for subsistence--as is the case for many impoverished ethnic minorities in Southeast Asia.
A social science study was carried out ancillary to a community-based cluster randomized trial on the effectiveness of LLIHs to control forest malaria. The social science research strategy consisted of a mixed methods study triangulating qualitative data from focused ethnography and quantitative data collected during a malariometric cross-sectional survey on a random sample of 2,045 study participants.
To meet work requirements during the labor intensive malaria transmission and rainy season, Ra-glai slash and burn farmers combine living in government supported villages along the road with a second home at their fields located in the forest. LLIH use was evaluated in both locations. During daytime, LLIH use at village level was reported by 69.3% of all respondents, and in forest fields this was 73.2%. In the evening, 54.1% used the LLIHs in the villages, while at the fields this was 20.7%. At night, LLIH use was minimal, regardless of the location (village 4.4%; forest 6.4%).
Despite the free distribution of insecticide-treated nets (ITNs) and LLIHs, around half the local population remains largely unprotected when sleeping in their forest plot huts. In order to tackle forest malaria more effectively, control policies should explicitly target forest fields where ethnic minority farmers are more vulnerable to malaria.
PLoS ONE 01/2012; 7(1):e29991. · 4.09 Impact Factor
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ABSTRACT: The entomological inoculation rate (EIR) is an important indicator in estimating malaria transmission and the impact of vector control. To assess the EIR, the enzyme-linked immunosorbent assay (ELISA) to detect the circumsporozoite protein (CSP) is increasingly used. However, several studies have reported false positive results in this ELISA. The false positive results could lead to an overestimation of the EIR. The aim of present study was to estimate the level of false positivity among different anopheline species in Cambodia and Vietnam and to check for the presence of other parasites that might interact with the anti-CSP monoclonal antibodies.
Mosquitoes collected in Cambodia and Vietnam were identified and tested for the presence of sporozoites in head and thorax by using CSP-ELISA. ELISA positive samples were confirmed by a Plasmodium specific PCR. False positive mosquitoes were checked by PCR for the presence of parasites belonging to the Haemosporidia, Trypanosomatidae, Piroplasmida, and Haemogregarines. The heat-stability and the presence of the cross-reacting antigen in the abdomen of the mosquitoes were also checked.
Specimens (N=16,160) of seven anopheline species were tested by CSP-ELISA for Plasmodium falciparum and Plasmodium vivax (Pv210 and Pv247). Two new vector species were identified for the region: Anopheles pampanai (P. vivax) and Anopheles barbirostris (Plasmodium malariae). In 88% (155/176) of the mosquitoes found positive with the P. falciparum CSP-ELISA, the presence of Plasmodium sporozoites could not be confirmed by PCR. This percentage was much lower (28% or 5/18) for P. vivax CSP-ELISAs. False positive CSP-ELISA results were associated with zoophilic mosquito species. None of the targeted parasites could be detected in these CSP-ELISA false positive mosquitoes. The ELISA reacting antigen of P. falciparum was heat-stable in CSP-ELISA true positive specimens, but not in the false positives. The heat-unstable cross-reacting antigen is mainly present in head and thorax and almost absent in the abdomens (4 out of 147) of the false positive specimens.
The CSP-ELISA can considerably overestimate the EIR, particularly for P. falciparum and for zoophilic species. The heat-unstable cross-reacting antigen in false positives remains unknown. Therefore it is highly recommended to confirm all positive CSP-ELISA results, either by re-analysing the heated ELISA lysate (100 °C, 10 min), or by performing Plasmodium specific PCR followed if possible by sequencing of the amplicons for Plasmodium species determination.
Malaria Journal 01/2011; 10:195. · 3.19 Impact Factor
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Delenasaw Yewhalaw,
Fantahun Wassie,
Walter Steurbaut,
Pieter Spanoghe, Wim Van Bortel,
Leen Denis,
Dejene A Tessema,
Yehenew Getachew,
Marc Coosemans,
Luc Duchateau,
Niko Speybroeck
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ABSTRACT: Indoor Residual Spraying (IRS), insecticide-treated nets (ITNs) and long-lasting insecticidal nets (LLINs) are key components in malaria prevention and control strategy. However, the development of resistance by mosquitoes to insecticides recommended for IRS and/or ITNs/LLINs would affect insecticide-based malaria vector control. We assessed the susceptibility levels of Anopheles arabiensis to insecticides used in malaria control, characterized basic mechanisms underlying resistance, and evaluated the role of public health use of insecticides in resistance selection.
Susceptibility status of An. arabiensis was assessed using WHO bioassay tests to DDT, permethrin, deltamethrin, malathion and propoxur in Ethiopia from August to September 2009. Mosquito specimens were screened for knockdown resistance (kdr) and insensitive acetylcholinesterase (ace-1(R)) mutations using AS-PCR and PCR-RFLP, respectively. DDT residues level in soil from human dwellings and the surrounding environment were determined by Gas Chromatography with Electron Capture Detector. An. arabiensis was resistant to DDT, permethrin, deltamethrin and malathion, but susceptible to propoxur. The West African kdr allele was found in 280 specimens out of 284 with a frequency ranged from 95% to 100%. Ace-1(R) mutation was not detected in all specimens scored for the allele. Moreover, DDT residues were found in soil samples from human dwellings but not in the surrounding environment.
The observed multiple-resistance coupled with the occurrence of high kdr frequency in populations of An. arabiensis could profoundly affect the malaria vector control programme in Ethiopia. This needs an urgent call for implementing rational resistance management strategies and integrated vector control intervention.
PLoS ONE 01/2011; 6(1):e16066. · 4.09 Impact Factor
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ABSTRACT: The status of knockdown resistance (kdr) mutation was investigated in the major malaria vector Anopheles arabiensis Patton (Diptera: Culicidae) from Ethiopia. Among 240 mosquito samples from 15 villages of southwestern Ethiopia that were screened by allele-specific polymerase chain reaction for kdr mutations, the West African kdr mutation (L1014F) was detected in almost all specimens (98.5%), whereas the East African kdr mutation (L1014S) was absent. Moreover, the mortality of An. gambiae s.l. to diagnostic dosages of 4% DDT, 0.75% permethrin, and 0.05% deltamethrin from bioassay results was 1.0%, 18.1%, and 82.2%, respectively. We report here the highest kdr allele frequency ever observed in An. arabiensis and its implications in malaria vector control in Ethiopia are discussed.
The American journal of tropical medicine and hygiene 07/2010; 83(1):122-5. · 2.59 Impact Factor
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ABSTRACT: The planned upscaling of vector control strategies requires insight into the epidemiological consequences of vector resistance. Therefore, the pyrethroid and DDT resistance status of Anopheles gambiae s.l. was assessed in Uganda from 2004 to 2006, and spatial and seasonal variations in knockdown resistance (kdr) frequencies were analyzed in terms of epidemiological significance. Anopheles gambiae s.l. was DDT and pyrethroid resistant in central and eastern Uganda. The L1014S kdr allele frequencies varied from 3% to 48% in An. gambiae s.s. Although the homozygous resistant genotype was the most prevalent genotype among survivors, the genotypes could not entirely explain the bioassay results. In the dry season, the kdr frequency was significantly higher in Plasmodium falciparum-infected mosquitoes, indicating that mosquitoes bearing a kdr mutation have a better adult survival, hence a higher likelihood of becoming infectious. This study showed that kdr might have an epidemiological impact that could jeopardize the vector control strategies.
The American journal of tropical medicine and hygiene 04/2010; 82(4):566-73. · 2.59 Impact Factor
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ABSTRACT: Malaria remains the most important public health problem in tropical and subtropical areas. Mothers' or caregivers' ability to recognize childhood malaria-related morbidity is crucial as knowledge, attitudes and health seeking behavior of caregivers towards childhood malaria could influence response to signs of the disease.
A total of 1,003 caregivers in 'at-risk' villages in close proximity to the Gilgel-Gibe hydroelectric dam in south-western Ethiopia, and 953 caregivers in 'control' villages further away from the dam were surveyed using structured questionnaires to assess their knowledge, perceptions and health seeking behaviour about childhood malaria.
Malaria (busa) was ranked as the most serious health problem. Caregivers perceived childhood malaria as a preventable ('at-risk' 96%, 'control' 86%) and treatable ('at-risk' 98% and 'control' 96%) disease. Most caregivers correctly associated the typical clinical manifestations with malaria attacks. The use of insecticide-treated nets (ITNs) was mentioned as a personal protective measure, whereas the role of indoor residual spraying (IRS) in malaria prevention and control was under-recognized. Most of the caregivers would prefer to seek treatment in health-care services in the event of malaria and reported the use of recommended anti-malarials.
Health education to improve knowledge, perceptions and health-seeking behaviour related to malaria is equally important for caregivers in 'at risk' villages and caregivers in 'control' villages as minimal differences seen between both groups. Concluding, there may be a need of more than one generation after the introduction of the dam before differences can be noticed. Secondly, differences in prevalence between 'control' and 'at-risk' villages may not be sufficient to influence knowledge and behaviour.
Malaria Journal 02/2010; 9:47. · 3.19 Impact Factor
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Wim Van Bortel,
Ho Dinh Trung,
Le Xuan Hoi,
Nguyen Van Ham,
Nguyen Van Chut,
Nguyen Dinh Luu,
Patricia Roelants,
Leen Denis,
Niko Speybroeck,
Umberto D'Alessandro,
Marc Coosemans
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ABSTRACT: In Vietnam, malaria is becoming progressively restricted to specific foci where human and vector characteristics alter the known malaria epidemiology, urging for alternative or adapted control strategies. Long-lasting insecticidal hammocks (LLIH) were designed and introduced in Ninh Thuan province, south-central Vietnam, to control malaria in the specific context of forest malaria. An entomological study in this specific forested environment was conducted to assess the behavioural patterns of forest and village vectors and to assess the spatio-temporal risk factors of malaria transmission in the province.
Five entomological surveys were conducted in three villages in Ma Noi commune and in five villages in Phuoc Binh commune in Ninh Thuan Province, south-central Vietnam. Collections were made inside the village, at the plot near the slash-and-burn fields in the forest and on the way to the forest. All collected mosquito species were subjected to enzyme-linked immunosorbent assay (ELISA) to detect Plasmodium in the head-thoracic portion of individual mosquitoes after morphological identification. Collection data were analysed by use of correspondence and multivariate analyses.
The mosquito density in the study area was low with on average 3.7 anopheline bites per man-night and 17.4 culicine bites per man-night. Plasmodium-infected mosquitoes were only found in the forest and on the way to the forest. Malaria transmission in the forested malaria foci was spread over the entire night, from dusk to dawn, but was most intense in the early evening as nine of the 13 Plasmodium positive bites occurred before 21H. The annual entomological inoculation rate of Plasmodium falciparum was 2.2 infective bites per person-year to which Anopheles dirus s.s. and Anopheles minimus s.s. contributed. The Plasmodium vivax annual entomological inoculation rate was 2.5 infective bites per person-year with Anopheles sawadwongporni, Anopheles dirus s.s. and Anopheles pampanai as vectors.
The vector behaviour and spatio-temporal patterns of malaria transmission in Southeast Asia impose new challenges when changing objectives from control to elimination of malaria and make it necessary to focus not only on the known main vector species. Moreover, effective tools to prevent malaria transmission in the early evening and in the early morning, when the treated bed net cannot be used, need to be developed.
Malaria Journal 01/2010; 9:373. · 3.19 Impact Factor
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ABSTRACT: In the Mekong region (Vietnam, Cambodia and Laos), a large investigation was conducted to assess the susceptibility of Anopheles species against DDT and pyrethroids. In this study, the resistance status of the potential malaria vectors An. vagus, An. sinensis, An. paraliae and An. peditaeniatus was assessed.
Bioassays were performed on field collected unfed female mosquitoes using the standard WHO susceptibility tests. In addition, the DIIS6 region of the para-type sodium channel gene was amplified and sequenced and four allele-specific PCR assays were developed to assess the kdr frequencies.
In Southern Vietnam all species were DDT and pyrethroid resistant, which might suggest the presence of a kdr resistance mechanism. Sequence-analysis of the DIIS6 region of the para-type sodium channel gene revealed the presence of a L1014S kdr mutation in An. vagus, An. sinensis and An. paraliae. In An. peditaeniatus, a low frequency L1014S kdr mutation was found in combination with a high frequency L1014F kdr mutation. For pyrethroids and DDT, no genotypic differentiation was found between survivors and non-survivors for any of these species. In the two widespread species, An. vagus and An. sinensis, kdr was found only in southern Vietnam and in Cambodia near the Vietnamese border.
Different levels of resistance were measured in Laos, Cambodia and Vietnam. The kdr mutation in different Anopheles species seems to occur in the same geographical area. These species breed in open agricultural lands where malaria endemicity is low or absent and vector control programs less intensive. It is therefore likely that the selection pressure occurred on the larval stages by insecticides used for agricultural purposes.
Parasites & Vectors 01/2010; 3(1):59. · 2.94 Impact Factor
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ABSTRACT: Despite Vietnam's success in reducing malaria mortality and morbidity over the last decade, malaria persists in the forested and mountainous areas of the central and southern provinces, where more than 50% of the clinical cases and 90% of severe cases and malaria deaths occur.
Between July 2005 and September 2006, a multi-method study, triangulating a malariometric cross-sectional survey and qualitative data from focused ethnography, was carried out among the Ra-glai ethnic minority in the hilly forested areas of south-central Vietnam.
Despite the relatively high malaria burden among the Ra-glai and their general awareness that mosquitoes can transmit an unspecific kind of fever (84.2%), the use of bed nets, distributed free of charge by the national malaria control programme, remains low at the farmers' forest fields where the malaria risk is the highest. However, to meet work requirements during the labour intensive malaria transmission and rainy season, Ra-glai farmers combine living in government supported villages along the road with a second home or shelter at their slash and burn fields located in the forest. Bed net use was 84.6% in the villages but only 52.9% at the forest fields; 20.6% of the respondents slept unprotected in both places. Such low use may be explained by the low perception of the risk for malaria, decreasing the perceived need to sleep protected. Several reasons may account for this: (1) only 15.6% acknowledged the higher risk of contracting malaria in the forest than in the village; (2) perceived mosquito biting times only partially coincided with Anopheles dirus ss and Anopheles minimus A true biting times; (3) the disease locally identified as 'malaria' was hardly perceived as having an impact on forest farmers' daily lives as they were unaware of the specific kind of fevers from which they had suffered even after being diagnosed with malaria at the health centre (20.9%).
The progressive confinement of malaria to minority groups and settings in the Greater Mekong sub-region implies that further success in malaria control will be linked to research into these specific socio-cultural contexts. Findings highlight the need for context sensitive malaria control policies; not only to reduce the local malaria burden but also to minimize the risk of malaria spreading to other areas where transmission has virtually ceased.
Malaria Journal 01/2010; 9:23. · 3.19 Impact Factor
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ABSTRACT: As insecticide resistance may jeopardize the successful malaria control programmes in the Mekong region, a large investigation was previously conducted in the Mekong countries to assess the susceptibility of the main malaria vectors against DDT and pyrethroid insecticides. It showed that the main vector, Anopheles epiroticus, was highly pyrethroid-resistant in the Mekong delta, whereas Anopheles minimus sensu lato was pyrethroid-resistant in northern Vietnam. Anopheles dirus sensu stricto showed possible resistance to type II pyrethroids in central Vietnam. Anopheles subpictus was DDT- and pyrethroid-resistant in the Mekong Delta. The present study intends to explore the resistance mechanisms involved.
By use of molecular assays and biochemical assays the presence of the two major insecticide resistance mechanisms, knockdown and metabolic resistance, were assessed in the main malaria vectors of the Mekong region.
Two FRET/MCA assays and one PCR-RFLP were developed to screen a large number of Anopheles populations from the Mekong region for the presence of knockdown resistance (kdr), but no kdr mutation was observed in any of the study species. Biochemical assays suggest an esterase mediated pyrethroid detoxification in An. epiroticus and An. subpictus of the Mekong delta. The DDT resistance in An. subpictus might be conferred to a high GST activity. The pyrethroid resistance in An. minimus s.l. is possibly associated with increased detoxification by esterases and P450 monooxygenases.
As different metabolic enzyme systems might be responsible for the pyrethroid and DDT resistance in the main vectors, each species may have a different response to alternative insecticides, which might complicate the malaria vector control in the Mekong region.
Malaria Journal 05/2009; 8:84. · 3.19 Impact Factor
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ABSTRACT: Ethiopia plans to increase its electricity power supply by five-fold over the next five years to fulfill the needs of its people and support the economic growth based on large hydropower dams. Building large dams for hydropower generation may increase the transmission of malaria since they transform ecosystems and create new vector breeding habitats. The aim of this study was to assess the effects of Gilgel-Gibe hydroelectric dam in Ethiopia on malaria transmission and changing levels of prevalence in children.
A cross-sectional, community-based study was carried out between October and December 2005 in Jimma Zone, south-western Ethiopia, among children under 10 years of age living in three 'at-risk' villages (within 3 km from dam) and three 'control' villages (5 to 8 km from dam). The man-made Gilgel-Gibe dam is operating since 2004. Households with children less than 10 years of age were selected and children from the selected households were sampled from all the six villages. This included 1,081 children from 'at-risk' villages and 774 children from 'control' villages. Blood samples collected from children using finger prick were examined microscopically to determine malaria prevalence, density of parasitaemia and identify malarial parasite species.
Overall 1,855 children (905 girls and 950 boys) were surveyed. A total of 194 (10.5%) children were positive for malaria, of which, 117 (60.3%) for Plasmodium vivax, 76 (39.2%) for Plasmodium falciparum and one (0.5%) for both P. vivax and P. falciparum. A multivariate design-based analysis indicated that, while controlling for age, sex and time of data collection, children who resided in 'at-risk' villages close to the dam were more likely to have P. vivax infection than children who resided farther away (odds ratio (OR) = 1.63, 95% CI = 1.15, 2.32) and showed a higher OR to have P. falciparum infection than children who resided in 'control' villages, but this was not significant (OR = 2.40, 95% CI = 0.84, 6.88). A classification tree revealed insights in the importance of the dam as a risk factor for malaria. Assuming that the relationship between the dam and malaria is causal, 43% of the malaria occurring in children was due to living in close proximity to the dam.
This study indicates that children living in close proximity to a man-made reservoir in Ethiopia are at higher risk of malaria compared to those living farther away. It is recommended that sound prevention and control programme be designed and implemented around the reservoir to reduce the prevalence of malaria. In this respect, in localities near large dams, health impact assessment through periodic survey of potential vectors and periodic medical screening is warranted. Moreover, strategies to mitigate predicted negative health outcomes should be integral parts in the preparation, construction and operational phases of future water resource development and management projects.
Malaria Journal 02/2009; 8:21. · 3.19 Impact Factor
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ABSTRACT: Malaria is re-emerging in most of the African highlands exposing the non immune population to deadly epidemics. A better understanding of the factors impacting transmission in the highlands is crucial to improve well targeted malaria control strategies.
A conceptual model of potential malaria risk factors in the highlands was built based on the available literature. Furthermore, the relative importance of these factors on malaria can be estimated through "classification and regression trees", an unexploited statistical method in the malaria field. This CART method was used to analyse the malaria risk factors in the Burundi highlands. The results showed that Anopheles density was the best predictor for high malaria prevalence. Then lower rainfall, no vector control, higher minimum temperature and houses near breeding sites were associated by order of importance to higher Anopheles density.
In Burundi highlands monitoring Anopheles densities when rainfall is low may be able to predict epidemics. The conceptual model combined with the CART analysis is a decision support tool that could provide an important contribution toward the prevention and control of malaria by identifying major risk factors.
PLoS ONE 01/2009; 4(11):e8022. · 4.09 Impact Factor
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ABSTRACT: Objectives and Methods In Burundi, the occurrence of the knock down resistance (kdr) mutation in Anopheles gambiae sensu lato (s.l.) was determined for six consecutive years within the framework of a vector control programme. Findings were also linked with the insecticide resistance status observed with bioassay in An. gambiae s.l. and An. funestus.Results The proportion of An. gambiae s.l. carrying the East Leu-Ser kdr mutation was 1% before the spraying intervention in 2002; by 2007 it was 86% in sprayed valleys and 67% in untreated valleys. Multivariate analysis showed that increased risk of carrying the kdr mutation is associated with spraying interventions, location and time. In bioassays conducted between 2005 and 2007 at five sites, An. funestus was susceptible to permethrin, deltamethrin and DDT. Anopheles gambiae s.l. remained susceptible or tolerant to deltamethrin and resistant to DDT and permethrin, but only when kdr allele carriers reached 90% of the population.Conclusions The cross-resistance against DDT and permethrin in Karuzi suggests a possible kdr resistance mechanism. Nevertheless, the homozygous resistant genotype alone does not entirely explain the bioassay results, and other mechanisms conferring resistance cannot be ruled out. After exposure to all three insecticides, homozygote individuals for the kdr allele dominate among the surviving An. gambiae s.l. This confirms the potential selection pressure of pyrethroids on kdr mutation. However, the high occurrence of the kdr mutation, even at sites far from the sprayed areas, suggests a selection pressure other than that exerted by the vector control programme.Objectifs et méthodes: Au Burundi, l’apparition de la mutation de résistance (kdr) chez Anopheles gambiae sensu lato (s.l.) a été déterminée sur six années consécutives dans le cadre d’un programme de lutte contre le vecteur. Les résultats ont également été comparés au statut de résistance aux insecticides observé d’après le test biologique chez An. gambiae s.l. et An. funestus.Résultats: La proportion d’An. gambiae s.l. portant la mutation Est kdr Leu-Ser était de 1% avant l’intervention par pulvérisation en 2002. En 2007, elle était de 86% dans les vallées pulvérisées et 67% dans les vallées non traitées. Une analyse multivariée a montré que l’augmentation du risque de porter la mutation kdr est associée aux interventions par pulvérisation, le lieu et la période. Dans des tests biologiques menés entre 2005 et 2007 dans cinq sites, An. funestusétait sensible à la perméthrine, au deltaméthrine et au DDT. An. gambiae s.l. est resté sensible ou tolérant au deltaméthrine et résistant à la perméthrine et au DDT, mais seulement lorsque les porteurs d’allèle kdr représentaient 90% de la population.Conclusions: La résistance croisée au DDT et à la perméthrine à Karuzi suggère un possible mécanisme de résistance kdr. Néanmoins, le génotype résistant homozygote seul ne suffit pas à expliquer entièrement les résultats du test biologique, et d’autres mécanismes conférant la résistance ne peuvent pas être exclus. Après exposition à l’ensemble des trois insecticides, les individus homozygotes pour l’allèle kdr dominaient parmi les survivants An. gambiae s.l.. Cela confirme le potentiel de la pression de sélection des pyréthroïdes sur la mutation kdr. Toutefois, la fréquence de la mutation kdr, même dans des sites éloignés des zones pulvérisées, suggère une pression de sélection autre que celle exercée par le programme de lutte contre les vecteurs.Objetivos & Métodos: En Burundi, la ocurrencia de la mutación knock-down resistance (kdr) en Anopheles gambiae sensu lato (s.l.) se determinó durante seis años consecutivos dentro del contexto de un programa de control vectorial. Los hallazgos se relacionaron también con el estatus de resistencia a insecticidas observado en un bioensayo con An. gambiae s.l. y An. funestus.Resultados: La proporción de An. gambiae s.l. con una mutación kdr East Leu-Ser fue del 1% antes de la intervención de rociamiento del 2002; en el 2007 era del 86% en valles en los que se había rociado y del 67% en valles sin tratar. Un análisis multivariado demostró que el riesgo aumentado de poseer una mutación kdr estaba asociado a las intervenciones de rociamiento, locación y tiempo. En bioensayos conducidos entre el 2005 y 2007 en cinco lugares diferentes, An. funestus era susceptible a permetrina, deltametrina y DDT. An. gambiae s.l. se mantenía susceptible o tolerante a deltametrina y resistente a DDT y permetrina, pero solo cuando los portadores del alelo kdr componían un 90% de la población.Conclusiones: La resistencia cruzada entre DDT y permetrina observada en Karuzi sugiere un posible mecanismo de resistencia kdr. Sin embargo, el genotipo homocigoto resistente por si solo no explica por completo los resultados del bioensayo, y otros mecanismos que confieren resistencia no pueden ser excluidos. Después de la exposición a los tres insecticidas, los individuos homocigotos para el alelo kdr se convirtieron en dominantes en la población de An. gambiae s.l. superviviente. Esto confirma la presión de selección que potencialmente ejercen los piretroides sobre la mutación kdr. Sin embargo, la frecuencia de la mutación kdr, aún en lugares lejanos a las áreas rociadas, sugiere una presión de selección diferente a la ejercida por el programa de control vectorial.
Tropical Medicine & International Health 11/2008; 13(12):1479 - 1487. · 2.80 Impact Factor
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ABSTRACT: In Burundi, the occurrence of the knock down resistance (kdr) mutation in Anopheles gambiae sensu lato (s.l.) was determined for six consecutive years within the framework of a vector control programme. Findings were also linked with the insecticide resistance status observed with bioassay in An. gambiae s.l. and An. funestus.
The proportion of An. gambiae s.l. carrying the East Leu-Ser kdr mutation was 1% before the spraying intervention in 2002; by 2007 it was 86% in sprayed valleys and 67% in untreated valleys. Multivariate analysis showed that increased risk of carrying the kdr mutation is associated with spraying interventions, location and time. In bioassays conducted between 2005 and 2007 at five sites, An. funestus was susceptible to permethrin, deltamethrin and DDT. Anopheles gambiae s.l. remained susceptible or tolerant to deltamethrin and resistant to DDT and permethrin, but only when kdr allele carriers reached 90% of the population.
The cross-resistance against DDT and permethrin in Karuzi suggests a possible kdr resistance mechanism. Nevertheless, the homozygous resistant genotype alone does not entirely explain the bioassay results, and other mechanisms conferring resistance cannot be ruled out. After exposure to all three insecticides, homozygote individuals for the kdr allele dominate among the surviving An. gambiae s.l. This confirms the potential selection pressure of pyrethroids on kdr mutation. However, the high occurrence of the kdr mutation, even at sites far from the sprayed areas, suggests a selection pressure other than that exerted by the vector control programme.
Tropical Medicine & International Health 11/2008; 13(12):1479-87. · 2.80 Impact Factor
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ABSTRACT: In a highland province of Burundi, indoor residual spraying and long-lasting insecticidal net distribution were targeted in the valley, aiming also to protect the population living on the hilltops. The impact on malaria indicators was assessed, and the potential additional effect of nets evaluated. After the intervention--and compared with the control valleys--children 1-9 years old in the treated valleys had lower risks of malaria infection (odds ratio, OR: 0.55), high parasite density (OR: 0.48), and clinical malaria (OR: 0.57). The impact on malaria prevalence was even higher in infants (OR: 0.14). Using nets did not confer an additional protective effect to spraying. Targeted vector control had a major impact on malaria in the high-risk valleys but not in the less-exposed hilltops. Investment in targeted and regular control measures associated with effective case management should be able to control malaria in the highlands.
The American journal of tropical medicine and hygiene 08/2008; 79(1):12-8. · 2.59 Impact Factor
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ABSTRACT: The distribution of anopheline mosquitoes in Vietnam was examined, with a particular interest for the two sibling species of the Anopheles minimus complex (Cellia: Myzomyia), An. minimus and Anopheles harrisoni, respectively former species A and C. Because the morphological identification of both sibling species is difficult and may lead to misidentifications, accurate data on their respective distribution are missing. This is of fundamental importance since the two species seem to exhibit differential vectorial capacities for malaria transmission.
Large entomological surveys based on cattle collections and molecular identifications of An. minimus s.l. were carried out in 23 sites throughout northern, central and south-eastern regions of Vietnam.
Based on previous molecular works and our data, the distribution of anopheline species and the relative densities of An. minimus and An. harrisoni were mapped. It is noteworthy that there was a high specific biodiversity at each study site. Anopheles minimus s.l. and Anopheles sinensis were the main anopheline species in the northern region, whereas Anopheles aconitus and Anopheles vagus were the most frequent ones in the central region. The southern limit of An. harrisoni was increased to the latitude of 11 degrees N. Sympatry between both sibling species has been extended to new provinces.
Malaria transmission is still high in central Vietnam and along bordering countries. Therefore, it is important to know and map the precise distribution of the main and secondary malaria vectors in Vietnam for applying efficient vector control programmes. Moreover, these maps should be regularly updated and linked to environmental characteristics relative to disease epidemiology, and environmental and climatic changes occurring in southeast Asia.
Malaria Journal 02/2008; 7:11. · 3.19 Impact Factor
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ABSTRACT: Based on their ecology, Rhipicephalus appendiculatus ticks from eastern and southern Africa have been divided into three groups. We investigated how two geographic genetically differentiated stocks of R. appendiculatus from the southern and the eastern provinces of Zambia, representing two ecological groups, i.e., southern African and transition groups, respectively, genetically compare to stocks from east Africa (Rwanda) and southern Africa (Zimbabwe and South Africa). The ITS2 and two mitochondrial genes segments, 12s rDNA and COI, were used in the investigations. The ITS2 tree did not show support for differentiation into any groups, while the two mitochondrial genes trees (12s rDNA and COI) showed two genetically differentiated groups: an east African genetic group which included specimens from Rwanda and the plateau area of the eastern province of Zambia, and a southern African genetic group represented by specimens from South Africa, Zimbabwe and specimens collected on the fringes of the eastern province plateau in the Nyimba district of Zambia. This suggests that the two geographically differentiated stocks of the southern and eastern provinces of Zambia might be part of two wider geographic genetically differentiated R. appendiculatus groups that extend beyond Zambia. Stocks of "transition" ecology (eastern province) belong to the east African genetic group and the differences in ecology within this genetic grouping may be due to genetic polymorphism, phenotypic plasticity, and other local factors.
Journal of Vector Ecology 01/2008; 32(2):168-75. · 0.88 Impact Factor
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ABSTRACT: Studies in the biology, ecology and behaviour of R. appendiculatus in Zambia have shown considerable variation within and between populations often associated with their geographical origin. We studied variation in the mitochondrial COI (mtCOI) gene of adult R. appendiculatus ticks originating from the Eastern and Southern provinces of Zambia. Rhipicephalus appendiculatus ticks from the two provinces were placed into two groups on the mtCOI sequence data tree. One group comprised all haplotypes of specimens from the Eastern province plateau districts of Chipata and Petauke. The second group consisted of a single haplotype of specimens from the Southern province districts and Nyimba, an Eastern province district on the fringes of the valley. This variation provides additional evidence to the earlier observations in the 12S rDNA and ITS2 data for the geographic subdivision of R. appendiculatus from Southern province and Eastern province plateau. The geographic subdivision further corresponds with differences in body size and diapause between R. appendiculatus from these geographic areas. The possible implications of these findings on the epidemiology of East Coast fever (ECF) the disease for which R. appendiculatus is one of the vectors are discussed.
Enperimental and Applied Acarology 02/2007; 41(1-2):129-38. · 1.73 Impact Factor
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ABSTRACT: African highlands often suffer of devastating malaria epidemics, sometimes in conjunction with complex emergencies, making their control even more difficult. In 2000, Burundian highlands experienced a large malaria outbreak at a time of civil unrest, constant insecurity and nutritional emergency. Because of suspected high resistance to the first and second line treatments, the provincial health authority and Médecins Sans Frontières (Belgium) decided to implement vector control activities in an attempt to curtail the epidemic. There are few reported interventions of this type to control malaria epidemics in complex emergency contexts. Here, decisions and actions taken to control this epidemic, their impact and the lessons learned from this experience are reported.
Twenty nine hills (administrative areas) were selected in collaboration with the provincial health authorities for the vector control interventions combining indoor residual spraying with deltamethrin and insecticide-treated nets. Impact was evaluated by entomological and parasitological surveys. Almost all houses (99%) were sprayed and nets use varied between 48% and 63%. Anopheles indoor resting density was significantly lower in treated as compared to untreated hills, the latter taken as controls. Despite this impact on the vector, malaria prevalence was not significantly lower in treated hills except for people sleeping under a net.
Indoor spraying was feasible and resulted in high coverage despite being a logistically complex intervention in the Burundian context (scattered houses and emergency situation). However, it had little impact on the prevalence of malaria infection, possibly because it was implemented after the epidemic's peak. Nevertheless, after this outbreak the Ministry of Health improved the surveillance system, changed its policy with introduction of effective drugs and implementation of vector control to prevent new malaria epidemics.
In the absence of effective drugs and sufficient preparedness, present study failed to demonstrate any impact of vector control activities upon the course of a short-duration malaria epidemic. However, the experience gained lead to increased preparedness and demonstrated the feasibility of vector control measures in this specific context.
Malaria Journal 02/2007; 6:93. · 3.19 Impact Factor
