Myxobolus cerebralis

Identification

Infection of fish causes whirling disease where fish swim aimlessly and may be deformed. They appear as 10 micrometer spores that are visually similar to other myxosporeans but are the only ones that can be found in salmonid cartilage.

Life Cycle

Two-host life cycle

Definitive host: salmonid fish (family Salmonidae)

Intermediate host: Tubifex worms (Tubifex tubifex)

This parasite infects a salmonid host. When it dies and decays, the durable myxospores that developed within the fish are consumed by tubifex worms. The spores anchor in the gut and multiply asexually in epithelial cells of the worms over 60-90 days and will be released for a duration of a year or more. They then swim through the water to infect fish through the skin or otherwise infect fish when worms are consumed. Inside fish cells, they reproduce asexually by asexual endogeny before eventually forming myxospores that will be released through decomposition of the fish.

https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/m/Myxobolus_cerebralis.htm

Host Information and Distribution

M. cerebralis causes whirling disease in salmon and trout and originated in Germany, where fish have developed resistance to infection. Over the last 50 years, occurrences have been observed elsewhere, facilitated by transfers of infected fish, who spread spores among each other, and the prevalence of tubifex worms, the parasites' intermediate hosts, of which thousands may exist in just a square yard of mud at the bottom of a river. Temperatures over 20 degrees celsius are not tolerated by the parasite.

https://www.cabi.org/isc/datasheet/73782