Recent advances in mosquito vector biology in coastal areas show global need to improve relevant public health policy

Title : Recent advances in mosquito vector biology in coastal areas show global need to improve relevant public health policy

Abstract:

Aedes aegypti and Aedes albopictus, the two most important vectors of arboviral diseases including dengue and Zika, are typical fresh water mosquitoes. However, they were recently observed to lay eggs and undergo preimaginal development in coastal brackish water collections (e.g. in fishing boats, beach debris and coastal wells) of up to 15 g/L salt in Sri Lanka’s Jaffna Peninsula and other countries^1-3. Compared with fresh water Aedes aegypti, brackish water Aedes aegypti in Jaffna display enhanced salt tolerance in egg hatching to adult development, differences in gene expression for cuticle structure-related proteins in larvae⁴, larval and adult cuticle structure and composition^4-6, as well as reduced susceptibilities to common larvicide and adulticides^5-6. Brackish water Aedes aegypti and Aedes albopictus are readily infected with dengue virus and transmit the virus transovarially to subsequent generations⁷. Dengue incidence increases in the Jaffna peninsula and inland areas of Sri Lanka with the onset of the annual seasonal rains³. Influential national and international guidelines for dengue control through vector source reduction ignore brackish water habitats of the two Aedes vectors⁸. The brackish water-developing Aedes therefore form a neglected reservoir of dengue virus to initiate epidemics in coastal areas that spread inland with the rains⁷. The important fresh water Asian malaria vectors Anopheles culicifacies and Anopheles stephensi were also recently shown to develop in coastal brackish water collections in the Jaffna peninsula and elsewhere in Sri Lanka^9-11. Findings suggest that:
(i) Salinity tolerance played a part in the rapid range expansion of Anopheles stephensi across South Asia and to the Horn of Africa¹¹.
(ii) Anopheles culicifacies developing in coastal brackish water habitats constitute a neglected malaria reservoir^9-10.
Furthermore, global warming leading to rising sea levels and increasing coastal groundwater salinisation is expected to increase the prevalence of diseases transmitted by salinity-tolerant mosquitoes and other vectors^12-13. Accumulation of brackish water-holding waste containers along coasts will have a similar impact. Aedes aegypti, and particularly Aedes albopictus, have expanded their range to temperate zone countries, causing indigenous transmission of arboviral diseases, e.g. in coastal areas of western Europe¹⁴. Elucidating the genetic basis for salinity tolerance in Aedes aegypti¹⁵ can lead to the development of more effective larvicides and adulticides for salinity-tolerant mosquito vectors in general. Addressing the brackish water development of important mosquito vectors for source reduction and overcoming insecticide resistance in national and international public health policies can therefore improve mosquito-borne disease control worldwide.

Biography:

Ranjan Ramasamy graduated in 1971 and obtained a PhD in 1974, both from the University of Cambridge, UK. He was the Chairman of the National Science Foundation of Sri Lanka, Professor of Life Sciences at the Institute of Fundamental Studies in Kandy in Sri Lanka, Professor of Biochemistry in the University of Jaffna in Jaffna Sri Lanka, Professor of Immunology in the University Brunei Darussalam Medical School, and held appointments at the Babraham Institute, Cambridge, UK and Scripps Clinic and Research Foundation, La Jolla, USA. He has more than 300 publications in molecular biosciences.