A geo-coded inventory of anophelines in the Afrotropical Region south of the Sahara: 1898-2016

Abstract

Background: Understanding the distribution of anopheline vectors of malaria is an important prelude to the design of national malaria control and elimination programmes. A single, geo-coded continental inventory of anophelines using all available published and unpublished data has not been undertaken since the 1960s. Methods: We have searched African, European and World Health Organization archives to identify unpublished reports on anopheline surveys in 48 sub-Saharan Africa countries. This search was supplemented by identification of reports that formed part of post-graduate theses, conference abstracts, regional insecticide resistance databases and more traditional bibliographic searches of peer-reviewed literature. Finally, a check was made against two recent repositories of dominant malaria vector species locations ( circa 2,500). Each report was used to extract information on the survey dates, village locations (geo-coded to provide a longitude and latitude), sampling methods, species identification methods and all anopheline species found present during the survey. Survey records were collapsed to a single site over time. Results: The search strategy took years and resulted in 13,331 unique, geo-coded survey locations of anopheline vector occurrence between 1898 and 2016. A total of 12,204 (92%) sites reported the presence of 10 dominant vector species/sibling species; 4,473 (37%) of these sites were sampled since 2005. 4,442 (33%) sites reported at least one of 13 possible secondary vector species; 1,107 (25%) of these sites were sampled since 2005. Distributions of dominant and secondary vectors conform to previous descriptions of the ecological ranges of these vectors. Conclusion: We have assembled the largest ever geo-coded database of anophelines in Africa, representing a legacy dataset for future updating and identification of knowledge gaps at national levels. The geo-coded database is available on Harvard Dataverse as a reference source for African national malaria control programmes planning their future control and elimination strategies.

Keywords: Africa; Anopheles; Malaria; Maps; Vectors.

Figure 1.. The spatial distribution of 13,331 Anopheline survey locations in Afrotropical Region south of the Sahara between 1898 and 2016.

4,494 sampling locations where survey dates included 2005–2016 shown in red.

Figure 2.. Distribution of sampled sites reporting presence of Anopheles gambiae complex (11,494), and sibling species, regarded as dominant vectors of malaria within their ecological range.

An. gambiae s.s (3,988 locations) is shown separately to allow for reporting that did not distinguish, for example, between An. coluzzii/M forms and An. gambiae S forms. An. gambiae s.s (S form) 1,574 locations, An. coluzzii 1,331 locations, An. arabiensis = 3,635 locations, An. melas 538 locations, An. merus 253 locations and An. bwambae 26 locations.

Figure 3.. Distribution of 5,052 sampled locations reporting the presence of Anopheles funestus s.l. (green) or where survey reports specified An. funestus s.s. (Blue) (n=727).

Figure 4.. Distribution of sampled locations reporting the presence of dominant vectors Anopheles nili s.l., An. moucheti and An. mascarensis.

( A) An. nili s.l. (n = 822 locations); ( B) An. moucheti s.l. (n = 499 locations), the two sites in Namibia were noted as unusual for this far south ( De Meillon, 1951) and ( C) An. mascarensis (n = 483 locations).

Figure 5.. Distribution of sampled locations of potential secondary malaria vectors ( Table 1).

( A) Anopheles funestus group: An. rivulorum (n = 244), An. leesoni (n = 187), An. parensis (n = 41) and An. vaneedeni (n = 34); the An. coustani group (n = 2,689) and where specified sibling species An. ziemanni (n = 662) and An. paludis (n = 375). ( B) An. squamosus (n= 1,294), An. pharoensis (n = 1,889), An. rufipes (n = 998), An. marshallii (n = 442), An. wellcomei (n = 272) and An. hancocki (n = 297).