Baseline spatial distribution of malaria prior to an elimination programme in Vanuatu

Pacific Malaria Initiative Support Centre (PacMISC), Australian Centre for International and Tropical Health (ACITH), School of Population Health, University of Queensland, Queensland, Australia.
Malaria Journal (Impact Factor: 3.49). 06/2010; 9:150. DOI: 10.1186/1475-2875-9-150
Source: PubMed

ABSTRACT The Ministry of Health in the Republic of Vanuatu has implemented a malaria elimination programme in Tafea Province, the most southern and eastern limit of malaria transmission in the South West Pacific. Tafea Province is comprised of five islands with malaria elimination achieved on one of these islands (Aneityum) in 1998. The current study aimed to establish the baseline distribution of malaria on the most malarious of the province's islands, Tanna Island, to guide the implementation of elimination activities.
A parasitological survey was conducted in Tafea Province in 2008. On Tanna Island there were 4,716 participants from 220 villages, geo-referenced using a global position system. Spatial autocorrelation in observed prevalence values was assessed using a semivariogram. Backwards step-wise regression analysis was conducted to determine the inclusion of environmental and climatic variables into a prediction model. The Bayesian geostatistical logistic regression model was used to predict malaria risk, and associated uncertainty across the island.
Overall, prevalence on Tanna was 1.0% for Plasmodium falciparum (accounting for 32% of infections) and 2.2% for Plasmodium vivax (accounting for 68% of infections). Regression analysis showed significant association with elevation and distance to coastline for P. vivax and P. falciparum, but no significant association with NDVI or TIR. Colinearity was observed between elevation and distance to coastline with the later variable included in the final Bayesian geostatistical model for P. vivax and the former included in the final model for P. falciparum. Model validation statistics revealed that the final Bayesian geostatistical model had good predictive ability.
Malaria in Tanna Island, Vanuatu, has a focal and predominantly coastal distribution. As Vanuatu refines its elimination strategy, malaria risk maps represent an invaluable resource in the strategic planning of all levels of malaria interventions for the island.

Download full-text


Available from: Andrew Tatem, Aug 13, 2015
  • Source
    • "For example, migrations across the international borders of Yunnan Province, China, which shares >4000 km of border with Myanmar, Lao People's Democratic Republic (PDR) and Vietnam, take place unchecked (Hu et al., 1998; Clements et al., 2009). Similarly, unmonitored migration of people across the border from Myanmar into Bangladesh jeopardizes the control efforts in Bangladesh (Reid et al., 2010) and imported infections from Yemen into Saudi Arabia continue to challenge Saudi elimination efforts (Alkhalife, 2003). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Movement of malaria across international borders poses a major obstacle to achieving malaria elimination in the 34 countries that have committed to this goal. In border areas, malaria prevalence is often higher than in other areas due to lower access to health services, treatment-seeking behaviour of marginalized populations that typically inhabit border areas, difficulties in deploying prevention programmes to hard-to-reach communities, often in difficult terrain, and constant movement of people across porous national boundaries. Malaria elimination in border areas will be challenging and key to addressing the challenges is strengthening of surveillance activities for rapid identification of any importation or reintroduction of malaria. This could involve taking advantage of technological advances, such as spatial decision support systems, which can be deployed to assist programme managers to carry out preventive and reactive measures, and mobile phone technology, which can be used to capture the movement of people in the border areas and likely sources of malaria importation. Additionally, joint collaboration in the prevention and control of cross-border malaria by neighbouring countries, and reinforcement of early diagnosis and prompt treatment are ways forward in addressing the problem of cross-border malaria. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Advances in Parasitology 06/2015; 89:79-107. DOI:10.1016/bs.apar.2015.04.002 · 4.36 Impact Factor
  • Source
    • "Despite the successes, malaria control remains a high priority for Viet Nam due to the threat of recrudescence or reintroduction into areas where control has been successful and due to evidence of declining efficacy of artemisinin based treatments in parts of the Mekong subregion (Delacollette et al., 2009; Dondorp et al., 2010). Spatial epidemiological tools are increasingly being used to estimate and represent malaria risk, and identify environmental correlates of risk (Brooker et al., 2006; Childs et al., 2006; Noor et al., 2008; Clements et al., 2009; Hay et al., 2009; Reid et al., 2010). At the national level, maps of disease risk can be powerful tools for advocacy and engaging policy makers and funders. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The malaria burden in Viet Nam has been in decline in recent decades, but localised areas of high transmission remain. We used spatiotemporal analytical tools to determine the social and environmental drivers of malaria risk and to identify residual high-risk areas where control and surveillance resources can be targeted. Counts of reported Plasmodium falciparum and Plasmodium vivax malaria cases by month (January 2007-December 2008) and by district were assembled. Zero-inflated Poisson regression models were developed in a bayesian framework. Models had the percentage of the district's population living below the poverty line, percent of the district covered by forest, median elevation, median long-term average precipitation, and minimum temperature included as fixed effects, and terms for temporal trend and residual district-level spatial autocorrelation. Strong temporal and spatial heterogeneity in counts of malaria cases was apparent. Poverty and forest cover were significantly associated with an increased count of malaria cases but the magnitude and direction of associations between climate and malaria varied by socio-ecological zone. There was a declining trend in counts of malaria cases during the study period. After accounting for the social and environmental fixed effects, substantial spatial heterogeneity was still evident. Unmeasured factors which may contribute to this residual variation include malaria control activities, population migration and accessibility to health care. Forest-related activities and factors encompassed by poverty indicators are major drivers of malaria incidence in Viet Nam.
    International Journal for Parasitology 01/2011; 41(1):109-16. DOI:10.1016/j.ijpara.2010.08.005 · 3.40 Impact Factor
  • Source
    • "Indeed, understanding socialecological contexts and health systems are of pivotal importance to comprehend the distribution of diseases of poverty, such as malaria and the so-called neglected tropical diseases (de Savigny and Adam, 2009; Utzinger et al., 2010). Such knowledge, in turn, is crucial for spatial targeting of control interventions and, in view of the ongoing malaria elimination programme, to provide more accurate predictions and more finetuned assistance to surveillance and elimination (Ostrom, 2009; Reid et al., 2010). "
Show more