Myxosporean infections of common carp (Cyprinus carpio)

Myxosporean infections in common carp (Cyprinus carpio) are responsible for a wide range of pathological findings and are well-known to cause heavy economical losses in the main carp producing countries in Europe and Asia. The complex two-host life cycle of myxosporean parasites obligatory relies on an invertebrate final host, typically an aquatic annelid worm and a vertebrate intermediate host, usually a fish. Each host type sheds a rather resistant infectious spore with a unique morphology. From a veterinary point of view, the intrapiscine development is most relevant. Actively or passively migrating presporogonic stages may obstruct fine capillaries in various organs and sporogony typically leads to large intra- or intercellular parasitic proliferation, the so-called plasmodia, which inflict a massive mechanical pressure before they eventually rupture, causing further tissue damage. The released myxospores may then trigger local or distant cellular host reactions, while others are shed to the environment. In this Diploma thesis, the author reviews the available literature to give an introduction to the pathological and parasitological dynamics of myxosporean infections in common carp. Furthermore, this thesis draws attention to seven clinicopathologically relevant myxosporean infections, their recognition, diagnosis, as well as prevention and treatment options. As an active member of the Fish Pathology and Parasitology research team, the author additionally worked on a series of field- and laboratory experiments aiming to identify and propagate myxosporeans obtained from a natural water body in Hungary. The author collected suitable invertebrate hosts from Kis-Balaton Resevoir, kept and checked them for released infective actinospore stages, identified the latter through a microscope, documented her findings photographically, obtained specimens for fish experimental infections, dissected the exposed Cyprinus carpio regularly and preserved samples for further PCR analysis. As a result, the neoactinomyxum type actinospores obtained from one oligochaete (B. sowerbyi) specimen successfully infected three SPF common carp fingerlings and the few consequently detected myxospores served as evidence for a successful intrapiscine development. They were identified as Thelohanellus sp. and later on, molecular data confirmed a putative new species