Adaptation of Anopheles mosquitoes to environmental changes in Southeast Asia and its implications for malaria transmission

Abstract

In South and Southeast Asia, vector-borne diseases pose a significant threat to public health. The most well-known vectors of disease pathogens are mosquitoes. Malaria, a protozoan infection that is transmitted by Anopheles mosquitoes, is one of the vector-borne diseases prevalent in tropical countries of Southeast Asia. Malaria parasites are transmitted to vertebrate hosts while mosquitoes feed on blood. Therefore, the rate of transmission and risk of infection are linked to mosquito blood-feeding behaviours and their local abundance in the area. The rate of transmission is significantly impacted by vectorial capacity, which is proportional to the number of infective bites, i.e. mosquitoes that prefer to feed on humans are much more likely to spread malaria since they bite humans repeatedly. The abundance of these vectors is contingent on favourable environments for their larvae and adults. Malaria transmission by mosquitoes is thus highly reliant on the surrounding environment. Southeast Asia was historically forested and would continue to be so in the absence of humans. The forests are the natural habitat of numerous insect species, including mosquitoes that originated in these ecosystems. Malaria transmission may decline for a period as a result of human cutting down the forests. Malaria risk may grow, however, if and when mosquito populations in forest-cleared regions change. This is due to the fact that the mosquito vectors will have evolved to feed on new hosts (in this case, humans, anthropophilic behaviour) and breeding in new environments (such as human-mediated environments), which will enhance malaria transmission. This study explains how environmental changes may affect mosquito adaptability and evolution in malaria-endemic regions of Southeast Asia. The evolution and adaptation of the malaria vectors have been studied in this thesis using both mitochondrial and nuclear markers. We were able to determine that the rich biodiversity of Southeast Asian Anopheles is not entirely recent but involves Plio-Pleistocene climatic fluctuations because of the region's dynamic biogeographical history. We were also able to identify species that had not been previously reported in this area before, using molecular identification methods. We are just starting to comprehend the ecological and evolutionary forces that have influenced the emergence of many vector-borne diseases. In order to reduce the risk of malaria in Southeast Asia, it is important to pay attention to our ecology and environment.

Date of Award	21 Apr 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Catherine Walton (Main Supervisor)