Learning More about Cryptosporidium in Cattle

Parasites previously thought to be Cryptosporidium parvum in post-weaned calves are actually different species altogether--species that infect cattle but not humans, according to Agricultural Research Service (ARS) studies.

ARS zoologist Ronald Fayer, biologist James Trout and visiting scientist Monica Santin of the Environmental Microbial Safety Laboratory in Beltsville, Md., found several types of Cryptosporidium in their studies, including C. parvum, C. andersoni and two unnamed genotypes.

In the studies, the scientists collected data from 15 dairy farms in seven states to determine the prevalence of Cryptosporidium species in pre-weaned and post-weaned calves. Fecal samples were analyzed to detect the parasite.

The prevalence of these Cryptosporidium species and genotypes appeared to be age-related between pre-weaned and post-weaned calves. C. parvum, the only Cryptosporidium species infectious to humans, made up 85 percent of the Cryptosporidium infections in pre-weaned calves, but only 1 percent of infections in post-weaned calves. It was formerly thought that C. parvum was present in all calves.

According to Fayer, these findings demonstrate that earlier reports on the presence and prevalence of C. parvum in post-weaned cattle, based solely on Cryptosporidium oocyst morphology, must be reassessed using molecular methods to validate species and genotype. Oocysts are the egglike, infectious form of the parasite.

Testing for Cryptosporidium is normally based on finding the parasite in fecal matter. These tests, however, prove the presence of Cryptosporidium but don't distinguish between different species.

Read more about the research in the May 2005 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief in-house scientific research agency.