Author
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Laegreid, William |
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Keen, James |
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Submitted to: Research Workers in Animal Diseases Conference Proceedings
Publication Type: Abstract Only Publication Acceptance Date: 10/11/2000 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Previous studies indicated EHEC O157 infection of beef calves on range in greater than 85% of herds examined at weaning. Prevalence of anti-O157 antibodies in calves in these herds was over 80%, suggesting that actual rates of infection were greater than estimated from a one-time sampling (7.4%). To understand the dynamics of transmission of EHEC O157 in beef calves, serum samples were obtained from a beef cow-calf herd approximatel every 6 weeks from birth until weaning for 3 consecutive years. Additional samples were obtained from most of these calves after entry into the feedlot. The presence of specific anti-O157 antibodies in these serum samples was detected using a blocking ELISA assay incorporating an anti- O157 monoclonal antibody. Using seroconversion data, the basic reproduction rate (Ro), defined as the number of secondary cases resulting from a single infected animal in a population of susceptible animals, was estimated for each of the 3 years as well as in aggregate. Ro for EHEC O157 infection in range beef calves varied from 2.9-5.6, with an average of 4.3 , CI95% 2.8-5.9. When Ro is less than 1, an infection cannot be maintained in a population, thus Ro is a useful predictor of the required efficacy of a control strategy. Given the above estimate of Ro, it is predicted that 77% of a herd of calves must be effectively vaccinated, or must be rendered non-susceptible through other means, to eliminate EHEC O157 infection from a herd. |
