Salmonid whirling disease: Myxosporean and actinosporean stages cross-react in direct fluorescent antibody test

Serologic relatedness of the two life stages of the salmonid whirling disease parasite Myxosoma cerebralis Hofer, 1903 — myxosporean spores from fish cartilage and actinosporean triactinomyxon spores from aquatic tubificids — were investigated. When the direct fluorescent antibody technique was used, anti-triactinomyxon and anti-M. cerebralis rabbit sera conjugated with fluorescein isothiocyanate cross-reacted with the respective heterologous life stage. Both stages showed similar locations of specific fluorescence with conjugates of either homologous or heterologous serum. Thus, serology supports the relatedness of the myxosporean M. cerebralis and the actinosporean triactinomyxon stages.