Asian tigers are facing a potentially deadly threat from a virus carried by domestic dogs, a wildlife expert with a British organization has warned. John Lewis, director of Wildlife Vets International, said there was evidence that Indonesian tigers were at risk from canine distemper virus, which has evolved in recent decades into a form that can infect other animals groups. \"If you wind the clock back about 30 or 40 years, it was a dog disease -- it was a canine virus and only affected dogs,\" Lewis told the BBC. \"But in the intervening years, the virus has evolved and has changed its pattern of animals it can infect to include marine mammals (such as seals) and big cats.\" The first case of the disease affecting wild big cats was documented close to two decades ago, he said. \"In the mid-1990s, in the Serengeti, Africa, about 30 percent of the lions died from CDV, which came from dogs in surrounding villages. \"It has [now] also been recognized in the Asian big cat populations,\" he said. Lewis said conversations with local wildlife vets on his recent visit to Sumatra seemed to indicate CDV could already be present in the population of the critically endangered Sumatran tiger. \"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.\"