Distribution of the main malaria vectors in Kenya

Abstract

Background: A detailed knowledge of the distribution of the main Anopheles malaria vectors in Kenya should guide national vector control strategies. However, contemporary spatial distributions of the locally dominant Anopheles vectors including Anopheles gambiae, Anopheles arabiensis, Anopheles merus, Anopheles funestus, Anopheles pharoensis and Anopheles nili are lacking. The methods and approaches used to assemble contemporary available data on the present distribution of the dominant malaria vectors in Kenya are presented here.

Method: Primary empirical data from published and unpublished sources were identified for the period 1990 to 2009. Details recorded for each source included the first author, year of publication, report type, survey location name, month and year of survey, the main Anopheles species reported as present and the sampling and identification methods used. Survey locations were geo-positioned using national digital place name archives and on-line geo-referencing resources. The geo-located species-presence data were displayed and described administratively, using first-level administrative units (province), and biologically, based on the predicted spatial margins of Plasmodium falciparum transmission intensity in Kenya for the year 2009. Each geo-located survey site was assigned an urban or rural classification and attributed an altitude value.

Results: A total of 498 spatially unique descriptions of Anopheles vector species across Kenya sampled between 1990 and 2009 were identified, 53% were obtained from published sources and further communications with authors. More than half (54%) of the sites surveyed were investigated since 2005. A total of 174 sites reported the presence of An. gambiae complex without identification of sibling species. Anopheles arabiensis and An. funestus were the most widely reported at 244 and 265 spatially unique sites respectively with the former showing the most ubiquitous distribution nationally. Anopheles gambiae, An. arabiensis, An. funestus and An. pharoensis were reported at sites located in all the transmission intensity classes with more reports of An. gambiae in the highest transmission intensity areas than the very low transmission areas.

Conclusion: A contemporary, spatially defined database of the main malaria vectors in Kenya provides a baseline for future compilations of data and helps identify areas where information is currently lacking. The data collated here are published alongside this paper where it may help guide future sampling location decisions, help with the planning of vector control suites nationally and encourage broader research inquiry into vector species niche modeling.

Figure 1

a-b. Map of Kenya showing the distribution of Anopheles gambiae sensu lato (a) and Anopheles funestus (b) (Roberts, 1974) displayed over the first-level administrative units (provinces). CE = Central Province; CO = Coast Province; EA = Eastern Province; NA = Nairobi Province; NE = North Eastern Province; NY = Nyanza Province; RV = Rift Valley Province; and WE = Western Province.

Figure 2

Map of Kenya showing the distribution of 492 spatially unique survey sites displayed over the first-level administrative units (Provinces) and the predicted PfPR_2-10 endemicity classes: PfPR_2-10> = 40%; PfPR_2-10 5-39%; PfPR_2-10 0.1% < 5%; and PfPR_2-10 < 0.1% [21]as shown in Figure legend.

Figure 3

a-f. Map of Kenya showing the distribution of spatially unique survey sites for a) Anopheles gambiae b) Anopheles arabiensis, c) Anopheles merus, d) Anopheles funestus, e) Anopheles pharoensis, f) Anopheles nili, displayed over the first-level administrative units (provinces) and predicted PfPR_2-10 endemicity classes: PfPR_2-10 > = 40%; PfPR_2-10 5-39%; PfPR_2-10 0.1% < 5%; PfPR_2-10 < 0.1% [21]as shown in Figure legend.