Dynamics of anopheline vector species composition and reported malaria cases during rain and dry seasons in two selected communities of Kwara State

Abstract

Indoor resting mosquitoes were collected between November 2013 and May 2014 using Pyrethrum spray collection (PSC). The mosquitoes were identified using morphological keys and species specific polymerase chain reaction (PCR) assays. The species composition of members of the An. gambiae complex and reported malaria cases in the selected study communities were spatially mapped using Arc GIS software. A total of 645 mosquitoes were collected from the study sites and morphologically identified. This comprised of 598 (92%) Anopheles species, 42 (7%) Culex species and 5 (1%) Aedes species. One hundredand ninety-six An. gambiaes. l. samples were randomly selected and successfully identified by PCR. The composition of the mosquitoes species collected in Gaa Bolohunduro showed that a higher proportion 53 (64.6%) were An. arabiensis compared to lower proportions 5(6.1%) of An. coluzzii and 24 (29.3%) An. gambiae. In Osin, only 12 (10.5%) were An. arabiensis compared to 13 (11.4%) and 89 (78.1%) identified as An. coluzzii and An. gambiae respectively. The variation in the composition of members of the An. gambiaes. l. identified in Gaa Bolohunduro was not significant (p=0.070) compared to Osin (p=0.043). A weak correlation coefficient showed that the predominance of Anopheles in both communities was not dependent on rainfall, though variation in the members of the complex within the wet and dry season was significant (p<0.01). The sympatric occurrence and availability of An. gambiaes. s. and An. arabiensis during the dry and wet seasons corroborated the high malaria prevalence identified in Ilorin South. This suggests that both vectors will sustain malaria transmission in the study sites. Hence, a vector control strategy in these localities should be informed by the individual behaviour of each vector species identified.

Keywords: Anopheles arabiensis, Anopheles coluzzi, Anopheles gambiae, distribution, composition, malaria case