Is the source of the distemper that infected Catalina Island’s foxes known?
No. The source is unknown. There are a number of possibilities: since distemper is always present, a weak strain could have mutated into a dangerous strain; or, something in the environment could have weakened the immune system of our fox, making the weakened distemper present deadly; or, a dog infected with distemper and brought to the Island could have been the source. We will never know for sure.