Prevalence of Cryptosporidium species and genotypes in mature dairy cattle on farms in eastern United States compared with younger cattle from the same locations.

Feces collected from 541 milking cows on two dairy farms each in Vermont, New York, Pennsylvania, Maryland, Virginia, North Carolina, and Florida were examined for the presence of Cryptosporidium oocysts. Oocysts were concentrated from 15 g of feces from each cow and DNA was extracted. A two-step nested PCR protocol was used to amplify an 830 base pair fragment of the SSUrRNA gene. PCR-positive products were purified and sequenced. PCR-positive findings were obtained from cows in all seven states and from 11 of 14 farms. Cryptosporidium parvum, Cryptosporidium bovis, and Cryptosporidium andersoni were found on 2, 6, and 8 farms, and infected 0.4, 1.7, and 3.7% of the 541 cows, respectively. The overall lower prevalence of Cryptosporidium in these cows was very highly significant (p< or =0.0001) compared with younger cattle and the relative prevalence of each species of Cryptosporidium also differed when compared with younger cattle previously examined on most of these same farms. The very low level of infection with C. parvum, the major species pathogenic to both cattle and humans, suggests that mature dairy cattle are a relatively low risk source of infection for humans.