Amur Tiger Populations Dying From Dog Disease [VIDEO]

Endangered Amur tiger populations are at "significant risk" form a viral disease most commonly found in dogs.

Reporting in the open-access journal mBio, a team of Russian and US researchers contend that canine distemper virus has killed at least one percent of the Siberian (Amur) tiger population since 2009.

While the figure may seem low, the researchers note that with an endangered animal like Amur tiger, every instance of species loss is significant.

"Losing one percent of an endangered population is pretty significant," said corresponding author Denise McAloose, Head Pathologist at the Wildlife Conservation Society in The Bronx, New York. "And these losses represent only the deaths we know about. I imagine that there were others that we just never saw," she said.

Once found throughout the Russian Far East, northern China and the Korean Peninsula, the Amur tiger was driven to the brink of extinction by the 1940s due to excessive hunting, when only an estimated 40 were left in existence, according to the World Wildlife Fund. Populations have since rebounded thanks to conservation efforts and the WWF reports there are now about 450 Amur tigers in the wild.

Canine distemper virus (CDV) is a contagious, largely incurable and frequently fatal disease that attacks an animal's body on multiple fronts. CDV targets the respiratory and digestive systems of animals, but the deadliest aspect of the disease targets the central nervous system -- causing the animals to be come disoriented and to not exhibit fear in situations where they normally would.

Since 2001 researchers have been noting incidents of the normally reclusive Amur tigers behaving strangely, including wandering out into busy Russian highways which they would usually be afraid of. Most of these tigers died or had to be euthanized after their condition worsened. CDV was suspected to have sickened the tigers, but this latest researchers provides more evidence that CDV is indeed to blame.

McAloose and her colleagues used tissue samples of five Amur tigers that were either dead or destroyed due to neurological disease in 2001, 2004 and 2010. Under a microscope, the brain tissues of the tigers were riddled with lesions, which indicated they suffered from viral encephalitis, consistent with their clumsy, abnormal behavior. Further testing revealed the presence of specific genes and proteins found in CDV.

McAloose said the problem was not isolated to one location, noting that the CDV-positive tigers were distributed across the Russian Far East.

"That tells us this is a disease that is distributed all across Amur tiger range," McAloose said. "And it also appears to be a relatively new threat to tigers since blood samples from wild tigers prior to 2000 tested negative for antibodies to the virus."

It's inconclusive how the tigers contracted CDV. Dogs, of course, are a suspect as tigers are known to kill and eat them. But other possible vectors could be raccoons or foxes.

McAloose and her colleagues are working to identify the exact source of CDV transmission to Amur tigers in the hopes that future infections can be stopped.

She said the "situation is quite serious" and that if gone unchecked CDV could possibly spell the demise of the Amur tiger.

"It's the first infectious disease that we know is a significant risk to Amur tiger survival," McAloose said.