Taxonomy and Systematics of Myxozoans (Cnidaria: Myxozoa) and Disease Epidemiology of Myxobolus cerebralis in the Southeast United States

Abstract

Myxozoa (Cnidaria) comprises over 2500 species of parasitic cnidarians infecting primarily freshwater, marine, and estuarine fishes. They represent some of the most demonstrable pathogens to cultured fishes including: Myxobolus cerebralis, the causative agent of whirling disease, Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease, and Henneguya ictaluri, the causative agent proliferative gill disease. Species that infect muscle can severely impact the value of wild caught fishes by either their appearance as white cysts in muscle, reducing marketability or in the case of some Kudoa species inducing myoliquifaction, commonly referred to as pudding flesh, rendering fish valueless. Myxozoans have a complex life cycle with an invertebrate definitive host (wherein the parasite matures) and a fish intermediate host (wherein asexual reproduction occurs). In this thesis 3 species of Myxobolidae are described and whirling disease is diagnosed from trout in the southeast US for the first time. I use taxonomy, histology, genetic sequencing (PCR; small subunit ribosomal DNA [18S]), and phylogenetic analysis to characterize three new species of assigned to two genera. Myxobolus neurofontinalis n. sp. from the central nervous system of brook trout, Salvelinus fontinalis, comprising the 2nd Myxobolus reported from a salmonid in the Southeastern US and the 7th from species of Salvelinus worldwide. Thelohanellus magnacysta n. sp., infecting the skeletal muscle of blacktail shiner, Cyprinella venusta, comprising the first myxozoan described from the blacktail shiner, the first Thelohanellus sp. reported from Cyprinella sp., and the fourth Thelohanellus sp. reported from North America. Myxobolus n. sp. infecting the skin of the imperiled cryptic sicklefin redhorse sucker, Moxostoma sp., comprising the first parasite reported from the sicklefin redhorse. Further, I provide an updated geographic distribution of M. cerebralis and use histology to provide the first diagnosis of whirling disease in wild trout from the southeast US. This work has resulted in manuscripts published or in review in Parasitology Research, Journal of Parasitology, Folia Parasitologica, and Journal of Fish Diseases.