Whirling Disease: Reviews and Current Topics

<EM>ABSTRACT. </EM>Whirling disease occurs in salmonid fishes infected by the myxosporean parasite <em>Myxobolus cerebralis</em>. This review summarizes the literature regarding control and management of the disease. Suggested methods for killing the myxospore stage include thorough drying, heating for 10 min at 90°C, calcium hydroxide at more than 0.5% for 24 h, and calcium oxide or KOH at more than 0.25% for 24 h. Chlorine was also effective at 1600 ppm in 24-h exposure or 5,000 ppm in a 10-min exposure. Roccal (alkyl dimethylbenzylammonium chloride) at more than 200 ppm active ingredient was also effective. Calcium cyanide at 4,000 kg/ha has been used effectively for control in infected ponds. Treating incoming water with 2537 Å of ultraviolet (UV) light at dosages greater than or equal to 35,000 microwatt-sec/cm² was effective in preventing infection of rainbow trout fry. Filtration of water through a 25 µm commercial filter cartridge did not reduce or eliminate the disease, but sand-charcoal filters have been used successfully in France. Prophylactic treatment of incoming water with 0.5 ppm chlorine for 2 h once a week over a 4 month period reduced infection by 63–73%. Electrical charges of 1–3 kV pulsed for 1–25 times at 99 µsec per pulse have killed a high proportion of the triactinomyxon stage. Triactinomyxons were also inactivated by 260 ppm chlorine as sodium hypochlorite, 10% hydrogen peroxide for 10 min, or 50% povidone-iodine for 10 min. Various drugs have been tested, some of which reduced the level of infection but failed to eliminate the parasite. Management strategies to control the disease include control of the worm host and its habitat, stocking larger fish into infected waters, not stocking infected fish, education, enforcement of disease regulations, and stocking less susceptible species.