The objective of this study was to compare a polymerase chain reaction (PCR) assay and a monoclonal antibody–based immunofluorescence assay (IFA) for detection of Cryptosporidium parvum in cat feces. Eight C. parvum–naive DSH cats were orally inoculated with 1 × 106 oocysts of a C. parvum human isolate. Fecal samples were collected before inoculation, daily for the next 30 days, and twice weekly until day 85. Methylprednisolone acetate was administered at 20 mg/kg i.m. on days 85, 92, and 99. From days 86 to 115, feces were collected daily and then up to twice weekly until day 126. Immunofluorescence assay was performed after collection of the samples, and then the samples were frozen at −70 C until assayed by PCR. Cryptosporidium parvum was detected by PCR in 101 of 353 samples and by IFA in 52 of 353 samples: 27 samples were PCR positive, IFA positive; 74 samples were PCR positive, IFA negative; 25 samples were PCR negative, IFA positive; and 227 samples were PCR negative, IFA negative. The percentage of concordance between IFA and PCR was 72%. Results of this study suggest that this PCR assay is more sensitive than IFA for detection of C. parvum in cat feces.

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