Do you recall the media reports suggesting that a cattle herd with cryptosporidiosis somehow contaminated a creek that emptied into Lake Michigan and ultimately caused illness of thousands of Milwaukee citizens?

That would be quite a trip even for this common protozoan parasite. In the Milwaukee case tests eventually concluded that the organism did not come from cattle, rather, the contamination was a result of water system filtration problems.

Sophisticated tests that enable the differentiation of genotypes have demonstrated that recent published outbreaks were caused by a cryptosporidium strain that infects only humans and is not found in cattle. These findings, reinforced by research at Cornell University, indicate that cattle are rarely, if ever, responsible for water-borne outbreaks of cryptosporidiosis in humans. (Dairy Herd Management, 39(12):10)

However, people working with livestock should be reminded that humans can contract cryptosporidiosis from animals or from contaminated water or materials. The infective organism can be found on a majority of cow-calf and dairy farms and is commonly shed by young calves, even in the absence of evidence of the disease.

Generally, cryptosporidiosis results in a transient diarrhea unless the condition is compromised by concurrent infection with other pathogens or the animal or person is immunocompromised.