Abstract
Heterosporosis is an increasingly important microsporidian disease worldwide, impacting wild and farmed raised fishes in both marine and freshwater environments. A previously undescribed species (Heterosporis sp.), with widespread distribution in the Great Lakes region, was the subject of this study. Three angler-caught fish were submitted to the Minnesota Veterinary Diagnostic Laboratory from 2009–2010 with lesions caused by intracellular proliferation of parasitic spores, resulting in destruction and eventual widespread necrosis of the host skeletal muscles. Mature ovoid (5.8 x 3.5μm) spores of a microsporidian parasite, consistent with the genus Heterosporis, were observed by light and electron microscopy. Molecular identification was performed using primer walking to obtain a near-complete rRNA gene sequence (~3,600 bp). A unique species of Heterosporis was identified, demonstrating less than 96% sequence identity to other published Heterosporis sp. on the basis of partial rRNA gene sequence analysis. Heterosporis sutherlandae n. sp. (formerly Heterosporis sp.) was identified in yellow perch (Perca flavescens), northern pike (Esox lucius) and walleye (Sander vitreus) from inland lakes in Minnesota and Wisconsin. Previous research suggests this species may be even more widespread in the Great Lakes region and should be reexamined using molecular techniques to better understand the distribution of this novel species.
Highlights
Microsporidian parasites infect a wide range of hosts, from single-celled protozoa to higher vertebrates, including humans
In areas of high spore concentration, a majority of the skeletal muscle cells were replaced by the parasites (Fig 2B)
This study of a previously unclassified microsporidian parasite identified a novel species of Heterosporis, H. sutherlandae, infecting fish in the Great Lakes region
Summary
Microsporidian parasites infect a wide range of hosts, from single-celled protozoa to higher vertebrates, including humans. More than 100 species of microsporidia in 15 genera have been identified in fishes [1–3]. Novel Microsporidian of Fish infections, they may cause reduced growth, anorexia, impaired swimming ability, reproductive defects and liquefaction of muscle tissues [4–11]. Members of the genera Heterosporis, Dasyatispora, Pleistophora, Kabatana, and the species in the undescribed group microsporidium are known to infect the skeletal muscles of susceptible fish hosts [3, 12–14]. Fish are exposed to the parasitic spores by consumption of an infected host or spores in the water column. The damage caused by the parasite gives filleted meat a freezer-burn appearance and renders the fish unfit for human consumption [15, 16]. Direct mortality of the host has been suggested in extreme cases [14], indirect parasite-induced mortality due to failure to capture prey or escape predation is likely
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