How The Crayfish Plague Can Spread

The plague is spread by natural diffusion and gradual movement over generations. It can also be spread through jump dispersal (movement over great distances). For the latter, it requires some kind of carrier (not necessarily a crayfish) to be moved from location to another. This can be caused by anglers who have handled crayfish as bait, feeding animals (such as raccoon, mink, fish, waterfowl, etc) or by vehicle (i.e. the transfer of boats from lake to lake).

This is why (one reason at least) I quarantine any feeders I use for my crayfish or purchase live foods from small stores that do their own breeding/raising/etc rather than from chain stores who often import large numbers from many locations (generally, whatever is the cheapest for them) where you may not be able to discern if they come with potential issues. And if possible, I will freeze or cook any food before feeding it to my crayfish to eliminate some of the potential for spores (and other bacteria, virus, etc) from being passed on to my crayfish or other tank inhabitants.

Additionally, this is why you should never house wild-caught and store-bought crayfish in the same aquarium (or putting store-bought crayfish in tanks that wild-caught crayfish had been living in, at least not without a thorough cleaning and waiting the appropriate amount of time that the spores/fungus last before dying off). And you should never mix any genus of crayfish, some genus have had exposure (and may carry the disease) while others have not (and have no immunity whatsoever).