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Objective—To determine the total number of Cryptosporidium parvum oocysts and Giardia spp cysts shed by dairy calves during the period when they are most at risk after natural infection.

Animals—478 calves naturally infected with C parvum and 1,016 calves naturally infected with Giardia spp.

Procedure—Oocysts or cysts were enumerated from fecal specimens. Distribution of number of oocysts or cysts versus age was used to determine the best fitting mathematic function. Number of oocysts or cysts per gram of feces for a given duration of shedding was computed by determining the area under the curve. Total number of oocysts or cysts was calculated by taking the product of the resultant and the expected mass of feces.

Results—Intensity of C parvum oocyst shedding was best described by a second-order polynomial function. Shedding increased from 4 days of age, peaked at day 12, and then decreased. An infected 6-day-old calf would produce 3.89 X 1010 oocysts until 12 days old. Pattern of shedding of Giardia spp cysts was best described by exponential functions. Intensity of shedding increased from 4 days of age, peaked at day 14, and then decreased. An infected calf would produce 3.8 X 107 cysts from day 50 until day 56.

Conclusion and Clinical Relevance—The large number of oocysts and cysts shed indicates that shedding by dairy cattle poses a risk for susceptible calves and people. Estimates reported here may be useful to aid in designing cost-effective strategies to manage this risk. (Am J Vet Res 2001;62:1612–1615)

Full access
in American Journal of Veterinary Research


Objective—To isolate and speciate Cryptosporidium DNA from fecal samples obtained from dairy cattle in New York State and identify factors associated with whether cattle were shedding Cryptosporidium parvum versus Cryptosporidium bovis.

Design—Cross-sectional study.

Sample Population—115 fecal samples positive for DNA coding for the Cryptosporidium 18S rRNA gene from dairy cattle in New York State.

Procedures—A PCR assay was used to amplify DNA from fecal samples; amplification products were submitted for bidirectional DNA sequencing. Logistic regression was used to test for associations between various host factors and Cryptosporidium spp.

Results—70 of the 115 (61%) fecal samples were found to have C parvum DNA, 42 (37%) were determined to have C bovis DNA, and 3 (3%) were found to have C parvum deer-type DNA. The presence of diarrhea at the time of fecal sample collection, oocyst count, and breed were associated with whether cattle were infected with C parvum or C bovis, with animals more likely to be infected with C parvum if they had diarrhea, had a high oocyst count, or were Holsteins.

Conclusions and Clinical Relevance—Results suggest that C parvum and C bovis can be isolated from dairy cattle in New York State and that various factors affect whether cattle infected with Cryptosporidium spp are infected with C parvum or C bovis. Findings also lend credence to the theory that C bovis may be more host adapted and thus less pathogenic to dairy cattle than C parvum.

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in Journal of the American Veterinary Medical Association


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 were generated for 200 samples. We can be certain, with 95% confidence, that cattle in the NYCW did not harbor C hominis.

Conclusions and Clinical RelevanceCryptosporidium infections in cattle are under examination because of the potential contamination of public waters by manure. Although cattle may be the source of zoonotic infection via C parvum, they pose little risk for C hominis (the strain commonly isolated from humans in waterborne outbreaks of disease). Other sources of oocysts should be considered when investigating outbreaks attributable to contaminated urban drinking water because cattle pose only a small risk via shedding of C hominis. (Am J Vet Res 2005;66:413–417).

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in American Journal of Veterinary Research