Quantifying parasite importation in an epidemic-prone zone of northern Kenya

点击翻译按钮获取中文摘要

Project summary Malaria elimination has been achieved or is within reach in several formerly endemic countries. As malaria transmission declines, imported malaria becomes an increasing threat to malaria control. Human movement is the major mechanism of importation and can lead to reintroduction of parasites into an ecosystem where malaria has been eliminated but vectors and hosts are still available. This could lead to re-establishment of transmission. Theoretical work predicts that frequent human circulation from endemic areas can sustain transmission in zones where malaria would otherwise naturally die out. Measuring the actual epidemiologic impact of imported malaria is challenging, but critical to our ability to design or measure the effects of interventions that target imported infections. In this study, we will directly measure the rate and downstream impact of imported infections in the Turkana region, a non-malaria-endemic area of northern Kenya. Turkana was previously epidemic-prone, but has become increasingly vulnerable to transmission due to; 1) changing land-use patterns that increase vector abundance, 2) transition from nomadic to settled communities, and 3) recent and dramatic growth in human circulation into the area as a consequence of oil exploration and extraction. First, we propose to measure the rate of importation of parasites through airport surveillance. In our study site, migration from malaria endemic areas is almost exclusively through the handful of weekly commercial flights into a small airstrip in the main town of Lodwar. By screening and testing passengers, we can directly measure the rate of importation in the study area. Second, we will describe the local epidemiology of malaria by establishing reactive case detection in four health facilities in the study area. Finally, we will compare parasite genotypes, and the diversity of genotypes, in imported versus locally acquired infections using a highly sensitive deep sequencing approach. By identifying the amount of diversity contributed from importation we can quantify the impact of importation on local transmission. Although the conditions in the study area are unique in the limited access points for movement into the region, in many other ways they reflect those facing many different parts of the developing world. Increased human settlement, changing land- use patterns, and enhanced movement are common across the tropics and subtropics. If transmission is being driven by importation in our study area, then it is most likely also happening in other places where it is far more difficult to measure. We expect the results of our study to culminate in the design of interventions to mitigate the threat of imported malaria as well as demonstrate how to measure the impact of these interventions through advanced, high-resolution genotyping techniques. Finally, the conditions facing Turkana are not only relevant to malaria. As recent outbreaks of dengue, polio, cholera, and Ebola have demonstrated, understanding importation is relevant for a broad range of infectious diseases in our increasingly connected world.