Anopheles mosquito larvae distribution patterns and seasonality of reported malaria cases in two communities in Lagos, Nigeria

Targeted allocation of malaria interventions to the most at-risk population heavily relies on formidable knowledge of the disease transmission seasonality, which in turn is a function of vector distribution patterns. The relationship between the distribution patterns of Anopheles mosquitoes and the seasonality of reported malaria cases was investigated. Monthly Anopheles larval data collected from 24 systematically selected sampling stations and reported malaria cases data obtained from Lagos State Ministry of Health surveillance records between January 2018 and June 2019 were analysed. Pearson correlation was used to analyse the relationship between larval count (LC) and MC. Epe had higher LC (53.2%), while Orimedu had higher MC (60.0%). The highest monthly LC in Orimedu (1178) and Epe (1323) occurred in Feb 2019, while the highest monthly MC (2886) occurred in May 2018 in Orimedu and in May 2019 in Epe (2157). There was weak positive correlation between LC and MC in Orimedu, r = 0.37, P > 0.05, whereas the correlation was negative in Epe, r = −0.13, P > 0.05. Low LC in Orimedu may reflect the short-lived nature of the dominating Anopheles larval breeding habitats (puddles), thereby limiting mosquito breeding to only the wet months. Conversely, the dominating habitats in Epe (perennial river and stream) provide year-round breeding habitats for mosquitoes, which may explain the observed high LC. The negative correlation of MC with LC in Epe may reflect the buffering influence of perennial habitats, where adult mosquito populations may emerge from stable sources that may not be consistently captured during larval sampling.