Risk factors for Anopheles mosquitoes in rural and urban areas of Blantyre District, southern Malawi

BackgroundAlthough urban malaria transmission is low and seasonal, it remains a major public health problem. This study aimed at demonstrating the presence of Anopheles mosquitoes and their potential to transmit malaria in urban settings.MethodsTwo cross-sectional surveys were carried out in Blantyre District, Malawi, during the dry and wet seasons of 2008 and 2010, respectively. A map of Blantyre was divided into a grid of 400 cells, of which 60 cells were randomly selected. Five households located within 100 m from the centre of each selected cell were enrolled, a standard questionnaire was administered, and indoor resting mosquitoes were sampled.ResultsIn 2008 and 2010, a total of 960 and 1045 mosquitoes were collected,  respectively. Anopheles funestus comprised 9.9% (n = 95) and 10.3% (n = 108) during the two surveys, respectively. Anopheles gambiae sensu lato (s.l.) was rarely detected during the second survey (n = 6; 0.6%). Molecular identification was performed on samples collected during the first survey, and An. funestus sensu stricto (s.s.) was the only sibling species detected. All the Anopheles mosquitoes were collected from households located in rural areas of Blantyre and none from urban areas. In univariate analysis, the presence of open eaves was associated with increased Anopheles prevalence, both during the dry (incidence rate ratio, IRR = 4.3; 95% CI 2.4 – 7.6) and wet (IRR = 2.47; 95% CI 1.7 – 3.59) seasons.  Chances of detecting Anopheles spp. decreased with increasing altitude (IRR = 0.996; 95% CI 0.995 – 0.997) and during the dry season, but increased during the wet season (IRR = 1.0017; 95% CI 1.0012 – 1.0023). These factors remained significant following a multiple Poisson regression analysis. No association was found between insecticide-treated bednet ownership and the number of Anopheles mosquitoes detected.ConclusionsThe presence of An. funestus s.s and An. gambiae s.l. in the periphery of Blantyre city was an indication that malaria transmission was potentially taking place in these areas

MOESM1 of Increasing insecticide resistance in Anopheles funestus and Anopheles arabiensis in Malawi, 2011–2015

Additional file 1: Table S1. Approximate locations of villages sampled from 2011 to 2015. Asterisks indicate latitude and longitude were estimated as the average of other villages in the same district or were estimated as the centroid of the district. Table S2. Mortality of An. funestus in WHO susceptibility tests against deltamethrin. 95% confidence limits and sample size are given in parentheses. Table S3. Mortality of An. funestus in WHO susceptibility tests against permethrin. 95% confidence limits and sample size are given in parentheses. Table S4. Mortality of An. funestus in WHO susceptibility tests against bendiocarb. 95% confidence limits and sample size are given in parentheses. Table S5. Mortality of An. funestus in WHO susceptibility tests against propoxur. 95% confidence limits and sample size are given in parentheses. Table S6. Mortality of An. funestus in WHO susceptibility tests against DDT. 95% confidence limits and sample size are given in parentheses. Table S7. Mortality of An. funestus in WHO susceptibility tests against malathion or pirimiphos-methyl (Chikwawa, Ntwana, 2015 only). 95% confidence limits and sample size are given in parentheses. Table S8. Mortality of An. arabiensis in WHO susceptibility tests against deltamethrin. 95% confidence limits and sample size are given in parentheses. Table S9. Mortality of An. arabiensis in WHO susceptibility tests against permethrin. 95% confidence limits and sample size are given in parentheses. Table S10. Mortality of An. arabiensis in WHO susceptibility tests against bendiocarb. 95% confidence limits and sample size are given in parentheses