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A new species of Myxobolus (Myxozoa: Bivalvulida) infecting the medulla oblongata and nerve cord of brook trout Salvelinus fontinalis in southern Appalachia (New River, NC, USA)

Myxobolus neurofontinalis n. sp. infects the brain and medulla oblongata of brook trout (Salvelinus fontinalis [Mitchill, 1814]) in the New River, western NC. It is the first species of Myxobolus described from the brook trout and resembles another congener (Myxobolus arcticus Pugachev and Khokhlov, 1979) that infects nerve tissue of chars (Salvelinus spp.). The new species differs from M. arcticus and all congeners bymyxospore dimensions and by having a mucous envelope and distinctive suturalmarkings. A phylogenetic analysis of the small subunit rDNA (18S) suggests that the new species shares a recent common ancestor with some isolates identified as M. arcticus and that the new species and its close relatives (except Myxobolus insidiosus Wyatt and Pratt, 1973) comprise a clade of salmonid nerve-infecting myxobolids. The phylogenetic analysis indicates that several isolates of “M. arcticus” (sensu lato) in GenBank are misidentified and distantly related to other isolates taken from the type host (Oncorhynchus nerka [Walbaum, 1792]) and from nearby the type locality (Kamchatka Peninsula, Russia). Serial histological sections of infected brook trout confirmed that myxospores of the new species are intercellular and infect nerve cord and medulla oblongata only. A single infected brook trout showed an inflammatory response characterized by focal lymphocytic infiltrates and eosinophilic granulocytes; however, the remaining 4 brook trout lacked evidence of a histopathological change or demonstrable host response. These results do not support the notion that this infection is pathogenic among brook trout.

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