Mosquitoes as Disease Vectors and Underlying Factors for Transmission

Mosquito-borne diseases pose a considerable public health problem globally as well as in India. Malaria, dengue, chikungunya, Zika, Japanese encephalitis and lymphatic filariasis are major mosquito-borne diseases in India. There are several species of mosquito vectors, but only a few are considered as vectors of diseases. Various reasons, like longevity, impact of climatic conditions, role of peritrophic membrane, presence/absence of microbiota in vectors, vectorial capacity, etc., have been put forth. As there is conflicting information on the climatic thresholds of transmission of malaria, dengue, chikungunya and Zika, the thresholds need to be backed up with reported data of a particular disease for public health implications of the projected data. Still a few species, like An. subpictus, are not considered as vector of malaria in India. Under what conditions the secondary vectors of malaria, like An. philippinensis, An. varuna and An. annularis, can become primary vectors, is not known. The penetration of peritrophic membrane by Plasmodium to the gut epithelial layer of Anopheles mosquito is facilitated by the chitinases secreted by Plasmodium, opening scope for development of chitinases inhibitor transgenic Anopheles vector, which can serve as transmission blocking vaccine. Studies have provided evidence that there is higher development of oocysts and sporozoites of Plasmodium in pyrethroid-resistant An. gambiae and An. funestus, while a few studies found no difference warranting further research. The presence of a particular species of microbiota inhibit the development of malaria parasite in mosquito, thus providing a way for transmission blocking. The quantification of repeated bites by mosquito vector for resulting into elephantiasis is not well elucidated. Filariasis is transmitted by many genera of mosquitoes, and the transmission of Zika virus is also not restricted to Aedes only. In the wake of elimination target of many diseases, like malaria and lymphatic filariasis, transmitted by mosquitoes, the role of a few mosquito vectors still needs to be elucidated. The present communication highlights a few thought-provoking issues warranting research.