Coustani Group mosquito (Diptera: Culicidae) diversity and malaria transmission in the Democratic Republic of the Congo

Background: The Democratic Republic of Congo is one of the countries with the heaviest burdens of malaria. To ensure that vector control tools, particularly insecticide-treated nets, remain effective as a prevention tool, entomological surveillance has been conducted throughout the country. In one location, early biting was noted by a majority of mosquitoes, morphologically identified as Anopheles paludis, a species in the Coustani Group, which had previously been found to transmit malaria in this country. The aim of this study was to better understand the Coustani Group species diversity, bionomics, and role in local malaria transmission in the DRC using both field and molecular approaches. 

Methods: Human landing collections and pyrethrum spray catches were conducted in Lodja, Kapolowe, and on one occasion, in Kenge. The mosquitoes were morphologically identified and processed in the laboratory. Enzyme linked immunosorbent assays and PCRs were conducted to determine whether mosquitoes carried Plasmodium sporozoites, and ITS2 and CO1 sequencing was conducted to identify species. Results: Anopheles paludis mosquitoes (as morphologically identified) were not found with sporozoites in Lodja, and only one specimen was found with sporozoites in Kapolowe. When the ITS2 and CO1 sequencing was conducted, there appeared to be two species groups in Lodja (where only An. paludis was identified morphologically) and four in Kapolowe (where An. paludis and Anopheles caliginosus were identified morphologically). There appeared to be differences between the species groups in terms of their biting times. 

Conclusions: The Coustani Group mosquitoes tested in this study did not appear to be major vectors of malaria, due to the low levels of detection of sporozoites in mosquitoes collected in and around houses in DRC, which differs from some studies previously conducted in DRC. However, this conclusion is complicated by the detection of four species groups, which may have different biting behaviour. Further work is necessary to ensure correct identification of species in order to understand the contribution of these species to malaria in DRC.