Assessment of mosquito species communities biting humans and their livestock in the forest hills of Karen state, Myanmar: a cross-sectional survey in six villages

Abstract

Background: Mosquito-borne diseases cause significant burdens in rural areas of Southeast Asia. The lack of data on vector bionomics hinders disease control and elimination. The objectives of this study were to assess the diversity and biting behaviours of mosquito species biting humans and their livestock in the forest hills of Karen state, Myanmar, and to assess the patterns of species co-occurrence and the effects of the environment on vector abundance. Methods: Mosquitoes were captured over 24-h diel cycles in six villages in September 2019 using the human landing catch and cow-baited trap collection methods. Collected specimens were identified to the species level using dichotomous morphological keys. Environmental data were acquired through remote sensing. The analysis of biting times was performed with circular statistics. Species co-occurrence patterns and the effects of environmental variables on species abundance were assessed with a generalized linear latent variable model. Results: A total of 36,607 mosquitoes were captured, and 96 species in 16 genera were identified. The most abundant genera were Anopheles, Culex and Downsiomyia. Multiple malaria, arboviruses and lymphatic filariasis vector species were detected, and their biting behaviours were reported. Generalized linear latent variable modelling revealed two clusters of species that were positively correlated with one another. The first cluster included many Culex and Anopheles species, and Mansonia annulata, which breed in shallow, stagnant or slow-moving water, such as marshes, swamps, rice fields and the margins of streams and puddles. These species were negatively associated with elevation, slopes and forests and positively associated with grasslands, shrubs and crop fields. The second cluster included many rainforest mosquitoes of the genera Armigeres, Heizmannia, Downsiomyia, Anopheles dirus, An. jeyporiensis, Culex bitaeniorhynchus and Aedes pseudoalbopictus, which breed in tree canopies and in natural surface water and containers such as bamboo stumps, tree holes and rainwater pools. These species were positively associated with elevation, slope, dense forests, surface water and wetlands and negatively associated with crop fields, grasslands and shrubs. Conclusions: Transmission dynamics are particularly complex in this setting where people are exposed to bites of numerous vector species throughout the diel cycle. Environmental factors shape the assembly of mosquito species communities and largely determine the risk of exposure to vector bites.