There's no better way to go from one pond to the next in a few hours' time, and within a week's time, perhaps, to fly the entire distance. We suspect that viruses could easily be transported on the feet or feathers of a bird. Or a net. Or a fisherman's boots. Or on salamanders that are used as fishing bait.
Human intervention is an obvious possibility.
There is much to learn about the survival and transmission of the virus over time, as well. The pond may later become reinfected or it may stay healthy. It is not clear how healthy animals are able to survive in previously infected ponds, or how the virus is reintroduced into uninfected areas. Why salamanders are susceptible to the disease, whereas frogs and fish sharing the same water escape infection, is also unclear. Davidson and Collins became even more concerned about the salamanders' predicament when they learned that other amphibians around the world were mysteriously dying, many of them in some of the world's most pristine habitat.