WYOMING


Yet another effect of this summer's drought has reared its ugly head in Wyoming: An unusually high number of cattle in the Cowboy State contracted deadly sulfate-induced polio in the summer months.


Merl Raisbeck of the University of Wyoming Veterinary Lab says that in an ordinary year he sees one or two polio cases in his lab. By June of this year, he had fielded hundreds of phone calls relating to sulfate-induced polio and performed eight or nine autopsies on animals that had contracted the disease.


The sulfur-laden groundwater common throughout the West is the primary cause of sulfate-induced polio, says Dan Gould at Colorado State University's Veterinary Diagnostic Lab. But in periods of low rainfall, sulfur becomes concentrated in well water and surface ponds, and hot temperatures force cattle to drink more water than usual. Polio is not prevalent in grazing wildlife like elk; veterninarians in Colorado and Wyoming think that's because wildlife are free to move to better water and drink less than cattle.


The microorganisms in a cow's digestive tract metabolize the sulfate ions into toxic hydrogen sulfide, similar in potency to hydrogen cyanide. High levels of sulfide cause irreversible brain damage, including damage to the brain's vision center. Ranchers usually identify the onset of sulfate-induced polio by an animal's "blind staggers." The disease is fatal 95 percent of the time. But there's some good news, according to Raisbeck: Late-summer rains have reduced the risk of the disease.