Characterization of Microhabitats of Arboviral Mosquito Vector Larvae on Three Islands of Lake Victoria, Kenya

Abstract

Mosquitoes are the primary vectors of arboviral infections. As there are no vaccines or effective therapeutic treatments for these diseases, vector control is an important approach for curbing their circulation or transmission. These vectors spend the first three of their four life stages in aquatic habitats where fitness and efficiency of adult mosquitoes to transmit arboviral infections is greatly influenced. Understanding ecology of mosquitoes in their aquatic habitats is therefore a critical component of vector control. This study investigated competent mosquito vectors present, their distribution and characteristics of their breeding habitats in three Lake Victoria Islands where high seroprevalence rates for arboviruses have been reported. Mosquito larvae sampled from Mfangano, Rusinga and Ngodhe Islands, were reared and identified by morphological and molecular means to determine mosquito distribution. Environmental variables including pH, temperature, nitrates, dissolved oxygen, ammonium, phosphate, copper, fluoride, salinity, conductivity, resistivity and oxidation reduction potential in the each of the sampled microhabitats were measured with a YSI photometer and professional plus water meter. Redundancy analysis and spearman correlation were used to determine association of each of these factors with three genera of mosquitoes sampled (Anopheles, Aedes and Culex). In addition, using Polymerase chain reaction, temperature gradient gel electrophoresis and 454 sequencing, bacteria in the microhabitats were profiled to determine their influence on mosquito breeding patterns. Competent vectors were present in the three Islands but their distribution varied based on island topography and size as well as human influence. Physico-chemical factors influence presence of larvae of each genus differently. Whereas presence of Aedes mosquito larvae had a strong positive correlation with ammonium rich microhabitats (pvalue = 0.0235), presence of Anopheles larvae had a significant positive correlation with microhabitat temperature (p-value =0.004). However, there was no significant correlation between any of the variables investigated with the presence of Culex mosquito larva. Bacteria from 29 phyla and 23 candidate phyla were present in larval microhabitats suggesting that mosquitoes breed in bacteria rich sites. Proteobacteria accounted for >40% of bacteria community composition in 86% of samples analyzed by 454 sequencing. Overall, there were differences in bacteria community composition even in microhabitats hosting similar mosquito species suggesting that bacteria alone do not influence breeding patterns. In conclusion, environmental factors, bacteria and human influence are important factors in determining presence and suitability of microhabitats to host mosquito larvae of a particular genus. Presence of Aedes in ammonium rich microhabitats suggests that use of ammonium rich fertilizers will indirectly encourage transmission of Aedes vectored arboviruses and hence should be monitored closely and farmers advised accordingly.