Distribution of Cryptosporidium parvum subtypes in calves in eastern United States.

Cryptosporidium parvum DNA from 175 neonatal calves on 16 farms in eight eastern states in the United States was subtyped by sequence analysis of the 60-kDa glycoprotein gene to determinate the parasite genetic diversity. Six subtypes of the IIa subtype family were found. Subtype IIaA15G2R1, which is the predominant C. parvum subtype in calves in many parts of the world, was identified in 77% of the C. parvum DNA from calves. Several farms had more than one C. parvum subtype and a few calves had infections with mixed subtypes. Distribution of subtypes differed geographically. Diversity of C. parvum in calves in eastern United States was lower than that previously seen in Michigan and southern Ontario. The high prevalence of one subtype in calves worldwide and frequent detection of this subtype in humans suggests that parasite fitness probably plays an important role in transmission of cryptosporidiosis among cattle and in zoonotic infections.