Tiger Populations Threatened by Dog Disease

A viral disease most commonly associated with dogs is threatening populations of tigers worldwide and has the potential to be deadly, according to the British nonprofit Wildlife Vets International.

The dog disease - known as canine distemper virus (CDV) - has evolved over the years and has come to affect a range of animals including ferrets, skunks, raccoons and big cats. Symptoms of CDV are gastrointestinal, respiratory and neurological -- increasingly severe seizures caused by CDV are often deadly. In big cats like tigers, a worrying neurological symptom recently reported is the cats' seeming loss of the fear of humans, which Wildlife Vets International says will increase the chance of human-tiger conflict and leave the animals more vulnerable to poachers.

"We have reports from Sumatra and other tiger range states that tigers are behaving abnormally and we need to know why," said John Lewis, a veterinarian and big cat expert, and also the co-founder of Wildlife Vets International. "Infection with canine distemper virus could explain at least some cases," he said in a report by the nonprofit.

"We need to find out how these cats are catching distemper, identify how and where they come into contact with domestic dogs which are the most likely virus source, and determine how best to tackle the problem. Otherwise we could lose even more of our vulnerable big cats," Lewis said.

For CDV to remain active, the disease has to have a reservoir, like a population of dogs, Lewis told the BBC, noting that in the mid-1990s in the Serengeti about 30 percent of the lions died from CDV contracted from dogs in surrounding villages.

CDV in tigers is still being studied and it is unclear how deadly tiger CDV will be. The disease is deadly in dogs about 50 percent of the time, as it causes their nervous system to degenerate, leading to a progressive deterioration of mental abilities and motor skills.

But being unfazed by humans is a worrying sign in diseased tigers, and reports of uncommon tiger behavior have been documented over the past decade, including instances of tigers wandering out into traffic and fearlessly entering villages.

At least three Siberian (Amur) tigers, the world's largest big cat, have died because of CDV, the British nonprofit reported, including one that was shot after it wandered into a village looking for food.

Lewis told the BBC that occurrences of erratic tiger behavior suggest CDV, but without a brain tissue analysis it's difficult to confirm. But it's clear the disease no longer just a threat to dogs.

"The big threats facing tigers are habitat loss and degradation and poaching, but I think the third big threat now is likely to be disease, particularly one like CDV," Lewis said.