The susceptibility of diverse species of cultured oligochaetes to the fish parasite Myxobolus pseudodispar Gorbunova (Myxozoa)

This study provides detailed information on the invertebrate hosts of Myxobolus pseudodispar (Myxozoa) and explores the susceptibility range of several species and analyses the relevance of the species composition of an oligochaete population. Our findings demonstrate that the oligochaete host range of M. pseudodispar is similarly wide as the number of vertebrate host species. Besides Tubifex tubifex and Limnodrilus hoffmeisteri, Psammoryctides barbatus and Psammoryctides moravicus were also found to be susceptible invertebrate hosts. The genetic characterization of the mitochondrial 16S rDNA of T. tubifex sensu lato revealed that lineages I, II and III are susceptible to M. pseudodispar, whereas T. tubifex lineage VI seems to be non-susceptible. T. tubifex lineage V and L. hoffmeisteri specimens were positive in a M. pseudodispar-specific PCR, but in most cases, the release of mature actinospores could not be detected. Hence, these non-susceptible oligochaetes likely serve as `biological filters` as they remove myxospores from the sediment without producing actinospores. Together with the phylogenetic analysis of the susceptible and non-susceptible oligochaete hosts on the basis of mt 16S rDNA sequences, the route of the development of M. pseudodispar in the oligochaete hosts was tracked by in situ hybridization. According to our findings, the gut epithelia seem to be a portal of entry of the sporoplasms, where the development of the parasite also takes place. The basal lamina seems to be involved in the migration of the parasite, and the worm's cellular immune response is activated by the infection.