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Applied and Environmental Microbiology, August 2003, p. 4604-4610, Vol. 69, No. 8
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.8.4604-4610.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Improved Quantitative Estimates of Low Environmental Loading and Sporadic Periparturient Shedding of Cryptosporidium parvum in Adult Beef Cattle

E. R. Atwill,1* B. Hoar,2 M. das Graças Cabral Pereira,1 K. W. Tate,3 F. Rulofson,4 and G. Nader5

Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California—Davis, Tulare, California 93274,1 Population Health and Reproduction, School of Veterinary Medicine,2 Department of Agronomy and Range Science, University of California—Davis, Davis, California 95616,3 University of California Cooperative Extension, Sonora, California 95370,4 University of California Cooperative Extension, Yuba City, California 959915

Received 3 February 2003/ Accepted 25 April 2003

Our primary goal was to generate an accurate estimate of the daily environmental loading rate of Cryptosporidium parvum oocysts for adult beef cattle, using immunomagnetic separation coupled with direct immunofluorescence microscopy for a highly sensitive diagnostic assay. An additional goal was to measure the prevalence and intensity of fecal shedding of C. parvum oocysts in pre- and postparturient cows as an indicator of their potential to infect young calves. This diagnostic method could detect with a >=90% probability oocyst concentrations as low as 3.2 oocysts g of feces-1, with a 54% probability of detecting just one oocyst g of feces-1. Using this diagnostic method, the overall apparent prevalence of adult beef cattle testing positive for C. parvum was 7.1% (17 of 240), with 8.3 and 5.8% of cattle shedding oocysts during the pre- and postcalving periods, respectively. The mean intensity of oocyst shedding for test-positive cattle was 3.38 oocysts g of feces-1. The estimated environmental loading rate of C. parvum ranged from 3,900 to 9,200 oocysts cow-1 day-1, which is substantially less than a previous estimate of 1.7 x 105 oocysts cow-1 day-1 (range of 7.7 x 104 to 2.3 x 105 oocysts cow-1 day-1) (B. Hoar, E. R. Atwill, and T. B. Farver, Quant. Microbiol. 2:21-36, 2000). Use of this highly sensitive assay functioned to detect a greater proportion of low-intensity shedders in our population of cattle, which reduced the estimated mean intensity of shedding and thereby reduced the associated environmental loading rate compared to those of previous studies.

* Corresponding author. Mailing address: Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California—Davis, Tulare, CA 93274. Phone: (559) 688-1731. Fax: (559) 686-4231. E-mail: ratwill{at}vmtrc.ucdavis.edu.

Applied and Environmental Microbiology, August 2003, p. 4604-4610, Vol. 69, No. 8
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.8.4604-4610.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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