A Plague on the Crayfish
(sporangium of Aphanomyces astaci)
Crayfish plague is a disease that is caused by the North American water mold Aphanomyces astaci. It was transmitted to Europe when North American species of crayfish called signal crayfish were introduced there. The North American crayfish were resistant to the pathogen but were also carriers, infecting the native crayfish population of Europe. Because the native crayfish were particularly susceptible to infection, this allowed the plague-coevolved signal crayfish to invade parts of Europe.
The transmission of crayfish plague is usually due to transport of disease-carrying signal crayfish, red swamp crayfish or infected native European freshwater crayfish between waters. Contamination can also occur through items that have been in contact with contaminated water, such as a fishing tool or footwear.
Infection with the crayfish plague is hard to spot or treat because the first indication of infection is often mortality. Otherwise, a symptom is the muscles of the tail appearing whitened or brownish-red. This happens because blood cells have encapsulated the hyphae. The effects of the neurotoxins in the mold can also cause the typically nocturnal crayfish to be active in daytime and lose coordination.
Crayfish plague has an unparalleled severity of effect. Infected susceptible crayfish do not survive – 100% mortality is normal. However, there is still hope. Some evidence suggests that previous exposure to sublethal numbers of the mold spores will increase the resistance of the crayfish to infection. The spores of crayfish plague also disappear from an infected water system in a few weeks after the last infected crayfish is gone, after which reintroduction is possible.
Photo credit: https://www.nobanis.org/globalassets/speciesinfo/a/aphanomyces-astaci/aphanomyces_astaci.pdf