Canine Distemper Virus is threatening tiger populations

The easily spread disease was once confined to dogs, but in recent decades, the virus has mutated to a form that can infect other mammals, such as seals, raccoons, hyenas and big cats, John Lewis, director of Wildlife Vets International, told the BBC.

"If you wind the clock back about 30 or 40 years, it … only affected dogs," Lewis said. "But in the intervening years, the virus has evolved."

The first reports of a CDV infection jumping to another species came from Africa. "In the mid-1990s, in the Serengeti, Africa, about 30 percent of the lions died from CDV, which came from dogs in surrounding villages," Lewis said.