No one has ever reported a wild orca dying from a mosquito-borne disease. But it's a different story for killer whales in captivity. In 1990, Kanduke, a 25-year-old male orca died suddenly at SeaWorld Orlando, the victim of encephalitis virus carried by a mosquito. And in 2007, Taku, a 14-yar-old male orca, died at SeaWorld San Antonio; unknown to his trainers, he'd been infected with West Nile Virus, the disease's tell-tale lesions spotted during a necropsy of his brain tissue. Captive orcas are particularly susceptible to these mosquito-borne diseases, scientists reported last month in the Journal of Marine Animals and Their Ecology, because of the shallow pools they're kept in. Two researchers observed seven captive orcas at SeaWorld in Florida for thousands of hours from 10:00 p.m. until 6:00 a.m., noting their behaviors. Most of the time, the whales stayed in a "logging" position, basically resting close to the surface. In the early evening hours, the scientists also observed mosquitoes landing on the animals' exposed dorsal fins for a meal. Captive orcas may also be more susceptible to these diseases, the scientists say, because they suffer from sunburn and broken, damaged teeth (as can be seen in the photo above of Keto), which weaken their immune systems. More captive orcas in the United States may be similarly infected, but the presence of such diseases is rarely noted in the National Oceanic and Atmospheric Administration's records of the animals' deaths, the scientists say. Instead, at least in Taku's case, the official cause of death was "pneumonia" without any reference to the bug bite.
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