Experimentally Induced Whirling Disease I. Dose Response of Fry and Adults of Rainbow Trout Exposed to the Triactinomyxon Stage ofMyxobolus cerebralis

Abstract

The intensity and prevalence of whirling disease was tested by exposure of 2-monthold fry and 1-, 2-, and 3.5-year-old adults of rainbow trout Oncorhynchus mykiss to a known number of laboratory-produced Myxobolus cerebralis at the actinosporean triactinomyxon stage. Fry exposed to graded concentrations of infectivity (triactinomyxons) for 3 h were individually examined for spores of Myxobolus cerebralis 5 and 6 months later. Exposure offish to the lowest doses, 1 and 10 triactinomyxons per fish, did not result in detectable myxosporean spores. Fish that became lightly infected by a dose of 100 triactinomyxons per fish experienced a decrease in the incidence of infection between 5 and 6 months after exposure. A linear relationship was found between the numbers of recovered myxosporean spores and doses of 100-10,000 triactinomyxons per fish, and the spore burden appeared to plateau at doses of 10,000-100,000 triactinomyxons per fish. Adult fish continuously exposed to the highest dose of triactinomyxons for 3.5 months were infected and asymptomatic; however, the severity of myxosporean infection decreased with increased age of fish. This information may help in controlling whirling disease in salmonids.

Identification of a serine protease gene expressed by Myxobolus cerebralis during development in rainbow trout Oncorhynchus mykiss

“…Prior research has shown that susceptibility to infection and severity of disease depend on fish species, parasite dose, age and size of the fish at the time of first exposure, and water temperature (Halliday 1976, O'Grodnick 1979, Markiw 1991, 1992, Hedrick et al 1999a,b, 2001, Vincent 2002. The life cycle of Myxobolus cerebralis and history of whirling disease have been well described, but the pathogenic mechanisms by which the parasite recognizes, invades, migrates, replicates, and induces host cell injury in both the fish and oligochaete hosts are largely speculative.…”

Effects of Whirling Disease on Selected Hematological Parameters in Rainbow Trout

“…Approximately 100 days post-exposure, triactinomyxon spores (TAMs) were released from the worm hosts and collected from the water with a 50 m wire mesh sieve for fish exposures. Microscopic examination of an aliquot of the filtered TAM suspension confirmed that the appearance of the TAMs was morphologically consistent with M. cerebralis (Markiw, 1986).…”

“…Whirling disease is clinically evident in infected salmonids through neurological and skeletal abnormalities including spinning or tail-chasing behavior, caudal hyperpigmentation (blacktail), and deformities of the cranium, operculum, and axial skeleton (Markiw, 1992a). Lesions associated with whirling disease are primarily associated with parasite infiltration of host neurological and skeletal tissues, and the degenerative and inflammatory changes that accompany them (Hedrick et al, 1991).…”

“…Lesions associated with whirling disease are primarily associated with parasite infiltration of host neurological and skeletal tissues, and the degenerative and inflammatory changes that accompany them (Hedrick et al, 1991). As whirling disease can be chronic and potentially impact host bioenergetics (Hoffman, 1974;Markiw, 1992b), it is likely that additional systemic changes may also occur. The objective of this study was to examine the effects of whirling disease on peripheral blood parameters among rainbow trout infected with M. cerebralis.…”

“…Repeat samples of filtered water from these tubificid worm stocks did not reveal the presence of quantifiable levels of any triactinomyxon spores. In September 1997, M. cerebralis spores (the infective stage for worm intermediate host) were obtained from the cranial skeletal tissues of adult rainbow trout with clinical whirling disease as described by Markiw and Wolf (1980). Approximately eight hundred of the tubificid worms were indefinitely exposed to aqueous solutions of the spores added to their aquaria at 1,000 spores/worm.…”