Ok, but leptospirosis is a bacterial infection, while (I think) OP's point was about dog distemper, which is caused by a virus. But according to Wikipedia this

Ok, but leptospirosis is a bacterial infection, while (I think) OP's point was about dog distemper, which is caused by a virus. But according to Wikipedia this is not a remote possibility (as the blog post puts it), but something that has actually already happened in several places, with disastrous consequences: > The domestic dog has largely been responsible for introducing canine distemper to previously unexposed wildlife and now causes a serious conservation threat to many species of carnivores and some species of marsupials. The virus contributed to the near-extinction of the black-footed ferret. It also may have played a considerable role in the extinction of the thylacine (Tasmanian tiger) and recurrently causes mortality among African wild dogs. In 1993-1994, the lion population in the Serengeti, Tanzania, experienced a 20% decline as a result of the disease. The disease has also mutated into the phocine distemper virus, which affects seals. (https://en.wikipedia.org/wiki/Canine_distemper https://en.wikipedia.org/wiki/Canine_distemper)