Risk of infection with Cryptosporidium parvum and Cryptosporidium hominis in dairy cattle in the New York City watershed.

Objective—To determine the risk posed by Cryptosporidium parvum and Cryptosporidium hominis from dairy cattle in the New York City watershed (NYCW). Sample Population—Samples from cattle at risk for shedding Cryptosporidium organisms on randomly selected dairy farms in the NYCW. Procedure—Feces were collected for 4 years from calves at risk for infection on 37 dairies. Oocysts were detected by use of centrifugation concentration-flotation microscopy. The DNA was directly isolated from fecal samples and used to amplify fragments of the small subunit ribosomal RNA and thrombospondinrelated adhesion protein C-2 genes by use of nested polymerase chain reaction assays. Small subunit ribosomal RNA fragments were restriction digested by the enzyme VspI and thrombospondin-related adhesion protein C-2 fragments were digested by Eco91I to distinguish between C hominis (formerly known as genotype 1) and C parvum (formerly known as genotype 2). Results—Of 437 fecal samples examined, 214 contained oocysts. Amplicons w...