The worm ingests spores of M. cerebralis which then develop into actinosporea in the gut epithelium of the worm. Although actinosporea have been classified as belonging to the genus Triactinomyxon , it seems that the organisms which comprise this genus may be intermediate forms of myxosporidian parasites. In short, taxonomists have yet to determine how these parasites will be classified. Clinical signs of whirling disease range from inapparent infection to erratic swimming and death. The abnormal swimming posture and tail-chasing behavior is caused by damage and deformity of the tail and spine secondary to the granulomatous chondritis induced by M. cerebralis.
Diagnosis is dependant on demonstrating the protozoa in tissue sections.
Vitamin C deficiency is also a common cause of scoliosis in salmonid fish and must be differentiated from infection with M. cerebralis . Montana Fish, Wildlife, and Parks, Helena, Montana. El-Matbouli, M. and Hoffman, R. 1989. Experimental transmission of two Myxobolus spp. Hoffman, G. L. 1990.