Myxosporea-induced xenoma formation in pike (Esox lucius L.) renal corpuscles associated with Myxidium lieberkuehni infection.

Myxidium lieberkuehni infection of the urinary tract of the pike (Esox lucius L.) is in most cases associated with the presence of cystic structures in renal corpuscles. These structures are greatly hypertrophic host cells constituting xenomas with the cytoplasm replete with proliferating myxosporean cells. Their development results in primary cells each enclosing one secondary and two tertiary cells. Eventually the cell structure assumes an appearance which suggests that the stages are no longer viable and most xenomas are destroyed by host tissue reaction. Some cells, however, may be released into the tubule lumen, suggesting a possible further sporogonic development of M. lieberkuehni. Circumstantial evidence points at the identity of the xenoma stages (designated Nephrocystidium pickii by Weissenberg in 1921, referenced in Weissenberg, 1923 [26]) with M. lieberkuehni, and this applies also to intracellular stages found in the epithelium of the collecting renal ducts. The latter have the same cell-in-cell arrangement of primary, secondary and tertiary cells, but were not observed to show any signs of cell degradation.