Culture of malacosporeans (Myxozoa) and development of control strategies for proliferative kidney disease

Abstract

Proliferative kidney disease (PKD) poses a high financial burden upon the freshwater salmonid aquaculture industry of Europe and North America. The alternate hosts of the causative agent, Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea), have been identified as freshwater bryozoans (Bryozoa: Phylactolaemata) within which spores capable of infecting salmonid fish develop. Currently, control of PKD relies upon complex management practices, with no licensed prophylaxis or treatment available.

Assessment of the nutritional preferences of phylactolaemate bryozoans allowed development of an optimised laboratory culture system. Following laboratory maintenance, bryozoans collected from PKD-endemic sites were found to be infected with the malacosporean parasites T. bryosalmonae and Buddenbrockia plumatellae. Subsequent parasitic development was observed using light-, electron- and confocal-microscopy techniques. Methods of challenging rainbow trout with T. bryosalmonae spores were developed, with the minimum infective dose established. The presence of Thomsen-Friedenreich and Tn epitopes within the parasite was investigated, and experimental vaccine preparations based on either these specificities or T. bryosalmonae-infected bryozoans were efficacy tested in rainbow trout. In addition, salinomycin and amprolium were tested as prospective chemotherapeutants for PKD.

Further insights into the development and subsequent release of malacosporean spores within their invertebrate hosts have been revealed. Long-term maintenance of T. bryosalmonae allowed controlled infection of rainbow trout previously vaccinated with experimental preparations. Findings of the project could potentially be utilised in future research into the development of control methods for PKD.