Field and laboratory evaluation of the microsporidia parasite, Heterosporis sutherlandae Prevalence, severity, and transmission

Journal of Aquatic Animal Health

Megan Tomamichel with a specimen in a necropsy lab. Photo credit: Maxwell Kleinhans

Corresponding Author: Megan Tomamichel

Summary by Ethan Hackmeyer

Heterosporis sutherlandae is a parasite that infects multiple species of fish in the Great Lakes region of North America. Once a fish is infected with H. sutherlandae, damage occurs to the musculoskeletal system reducing the viability of the fish, while also making it unfit for human consumption. Despite the ecological and economic impacts of this parasite, little is known about its disease dynamics. To bridge the current gap in knowledge on the parasitic interactions between H. sutherlandae and various fish species living in the Great Lakes region, CEID Member and PhD Student Megan Tomamichel evaluated the presence, severity and transmission of the parasite both in laboratory conditions as well as in nature.

In order to test for the natural presence of H. sutherlandae, samples were analysed from Cass Lake, Leech Lake and Lake Winnibigoshish, all of which are economically important lakes located in Minnesota. Fish sampled were categorized by their species, gender, length and weight, as well as the season they were caught. Fish were checked under a microscope for the presence of H. sutherlandae, and samples that showed spore presence were marked as positive.

To better understand H. sutherlandae disease dynamics, the authors led experiments within a controlled lab setting. Fathead minnows, known to be susceptible to the parasite, were infected in two different ways: exposure through cohabitation with infected individuals, and exposure from feeding on infected tissue that was collected from the wild. After eight weeks, the fish were analyzed for signs of infection.

In the samples of the wild fish from the Minnesotan lakes, prevalence of H. sutherlandae was found to be anywhere from 1% – 11% depending on the time of year as well as species. Prevalence was found to be lowest during the colder months, and Yellow Perch were found to have a relatively higher prevalence of H. sutherlandae than other species. Notably, Yellow Perch with their highest infection rate at 11% being observed during the summer, fell far short of the recorded value of 28% during 2004. This indicates a possible shift in the disease dynamic that prompts further research.

From the laboratory experiment, the main transmission pathway was found to be ingestion of infected tissue. Only 2% of minnows cohabitating with infected fish were found to be infected, however 23% of fish that ate infected tissue were found harboring H. sutherlandae. This indicates that the key to reducing infection rates could be ensuring that infected individuals are not eaten, and commercial fisheries should be wary when feeding their fish tissue that could be contaminated by H. sutherlandae in order to prevent costly breakouts.

This research was completed by Tomamichel during her Masters of Science program at the University of Minnesota, along with collaborators Paul Venturelli of Ball State University and Nicolas Phelps of the University of Minnesota.

Tomamichel MM, Venturelli PA, Phelps NBD. Field and laboratory evaluation of the microsporidia parasite, Heterosporis sutherlandae Prevalence, severity, and transmission. J Aquat Anim Health. 2020 Dec 28. doi: 10.1002/aah.10122. Epub ahead of print. PMID: 33369794.

Image on home page of perch in cooler provided by Luis Escobar