We may think aquatic animals are not exposed to mosquito bites. However, some of them are. For example captive killer whales, which are exposed to mosquito-borne infections such as West Nile virus.

West Nile virus (WNV)is an arbovirus (acronym for arthropod-borne virus, term used for viruses spread by arthropod vectors), and it is transmitted through the bite of mosquitoes of the genus Culex. Birds are its natural hosts, but a variety of mammals are susceptible to infection and WNV is now a significant cause of human viral encephalitis worldwide.

Also marine mammals kept in captivity, such as killer whales, can catch it with severe consequences. WNV was implicated in the death of a killer whale in a Texas marine park in 2007. Before then, in 1990 another whale died at SeaWorld in Florida due to another arbovirus transmitted by Culex mosquitoes, this time the St. Louis encephalitis (SLE) virus. Also wild cetaceans living in shallow inland waters seem to be exposed to mosquito-borne viruses, as shown in 2009 with the detection of antibodies against WNV in dolphins from marshes and mangroves in Florida and South Carolina.

According to experts observing and working with captive killer whales, these animals are at risk of arboviral disease for various reasons. Mosquitoes have been observed landing on captive orcas which, compared to their wild counterparts, spend more time stationing on the water surface (a behaviour commonly called logging) with their bodies exposed to bites. Also a prolonged exposure to ultraviolet radiation (UVR), common in shaded enclosures in marine parks, may have immunosuppressant effects on the animals rendering them more susceptible to infections and severe pathology.

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REFERENCES

St. Leger, J., Wu, G., Anderson, M., Dalton, L., Nilson, E., Wang, D., 2011. West Nile Virus Infection in Killer Whale, Texas, USA, 2007. Emerg. Infect. Dis. 17. https://doi.org/10.3201/eid1708.101979

Buck, C., Paulino, G.P., Medina, D.J., Hsiung, G.D., Campbell, T.W., Walsh, M.T., 1993. Isolation of St. Louis encephalitis virus from a killer whale. Clin. Diagn. Virol. 1, 109–112. https://doi.org/10.1016/0928-0197(93)90018-Z

Schaefer, A.M., Reif, J.S., Goldstein, J.D., Ryan, C.N., Fair, P.A., Bossart, G.D., 2009. Serological Evidence of Exposure to Selected Viral, Bacterial, and Protozoal Pathogens in Free-Ranging Atlantic Bottlenose Dolphins (Tursiops truncatus) from the Indian River Lagoon, Florida, and Charleston, South Carolina. Aquat. Mamm. 35, 163–170. https://doi.org/10.1578/AM.35.2.2009.163

Jett, J., Ventre, J., 2012. Orca (Orcinus orca) captivity and vulnerability to mosquito-transmitted viruses. J. Mar. Anim. Their Ecol. 5, 9-16. http://www.oers.ca/journal/volume5/issue2/caseReport_vol5iss2.pdf

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