Heterosporis sutherlandae
Heterosporosis is caused by the obligate intracellular parasite, Heterosporis sutherlandae. First confirmed in Minnesota and Wisconsin in 2000, H. sutherlandae is now found in ~50 lakes across the Eastern Great Lakes region and known to infect ~15 species of fish of economic and ecological importance. The parasite essentially liquefies the skeletal muscle tissue of infected fish rendering the fillets unpalatable for human consumption. Consequently, H. sutherlandae has been listed as a pathogen of concern by state agencies and the Great Lakes Fish Health Committee.
More background on H. sutherlandae can be found here.
Describing Heterosporis sutherlandae:
Our first step in understanding this parasite was to formally describe the species. We assigned the species name 'H. sutherlandae' after Dr. Dan Sutherland who led much of the early work on this parasite at the University of Wisconsin - La Crosse. More information on the morphological and molecular characterization can be found here:
Funding: Minnesota Environment and Natural Resource Trust Fund.
Improved detection and survey:
Detection of H. sutherlande has relied on gross observations of muscle tissue. While a simple approach, the sensitivity and specificity was a major concern. We developed and validated a qPCR assay for rapid detection and used the new test to perform a survey of Minnesota lakes and fish farms. We found that our detection ability improved with the use of PCR, compared to visual or microscopic examination, and suggest that this be used for future surveillance testing.
Funding: Minnesota Environment and Natural Resource Trust Fund.
Prevalence and potential impacts to a Minnesota fishery:
We conducted a survey of Leech Lake (Cass County, MN) and found a 28% prevalence of the parasite in Yellow Perch. The survey results suggest that males are more susceptible to infection, that infection is not associated with maturity or a gape-limiting food source and that heterosporosis increases in severity with time or by increased exposure. To predict impacts, we developed an equilibrium yield model and found that a 10% increase in mortality due to H. sutherlandae could result in 30% and 10% reductions in yield and mean catch weight, respectively. More details can be found here:
Funding: Minnesota Aquatic Invasive Species Research Center and the Minnesota Environment and Natural Resource Trust Fund.
Prevalence, severity, and transmission:
Field sampling and laboratory experiments suggest that H. sutherlandae has low-moderate transmission rates (tissue fed=23%, cohabitation=2%) and overall low prevalence once established in wild fish populations (1-11%), which higher rates during the summer and in yellow perch. Detailed methods and results are currently under review:
Funding: Minnesota Aquatic Invasive Species Research Center and the Minnesota Environment and Natural Resource Trust Fund.
