Myxobolus cerebralis in Tubifex tubifex from a whirling disease epizootic in Montana.

Aquatic oligochaetes from a whirling disease enzootic area in southwest Montana were examined for infection with Myxobolus cerebralis. Anterior portions of oligochaetes were preserved for specific identification, whereas DNA was purified from posterior portions. The purified DNA was used in a nested polymerase chain reaction (PCR) assay specific for M. cerebralis small-subunit ribosomal DNA. Naturally infected oligochaetes were identified by a resulting 415-bp fragment of amplified parasite DNA. A total of 704 oligochaetes was tested from April through September 1997. Eighteen (2.6%) oligochaetes were infected with M. cerebralis as defined by the nested PCR assay. Two of these were identified as mature Tubifex tubifex, and the others were likely T. tubifex but were immature and lacking the diagnostic reproductive structures. This is the first report of T. tubifex naturally infected with M. cerebralis.