Orca (Orcinus orca) captivity and vulnerability to mosquito-transmitted viruses

Although unreported in wild orca populations, mosquito-transmitted diseases have killed at least two captive orcas (Orcinus orca) in U.S. theme parks. St. Louis Encephalitis Virus (SLEV) was implicated in the 1990 death of the male orca Kanduke, held at SeaWorld of Florida. In the second case, West Nile Virus (WNV) killed male orca Taku at SeaWorld of Texas in 2007. Captive environments increase vulnerability to mosquitotransmitted diseases in a variety of ways. Unlike their wild counterparts who are rarely stationary, captive orcas typically spend hours each day (mostly at night) floating motionless (logging) during which time biting mosquitoes access their exposed dorsal surfaces. Mosquitoes are attracted to exhaled carbon dioxide, heat and dark surfaces, all of which are present during logging behavior. Further, captive orcas are often housed in geographic locations receiving high ultraviolet radiation, which acts as an immunosuppressant. Unfortunately, many of these facilities offer the animals little shade protection. Additionally, many captive orcas have broken, ground and bored teeth through which bacteria may enter the bloodstream, thus further compromising their ability to fight various pathogens. Given the often compromised health of captive orcas, and given that mosquito-transmitted viral outbreaks are likely to occur in the future, mosquito-transmitted diseases such as SLEV and WNV remain persistent health risks for captive orcas held in the U.S. [JMATE. 2012;5(2):9-16]