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Title: ESTIMATION OF THE BASIC REPRODUCTION RATIO (RO) FOR SHIGA TOXIN-PRODUCING ESCHERICHIA COLI O157:H7 (STEC O157) IN BEEF CALVES

Author
item Laegreid, William
item Keen, James

Submitted to: Epidemiology and Infection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2003
Publication Date: 4/1/2004
Citation: Laegreid, W.W., Keen, J.E. 2004. Estimation of the basic reproduction ratio (ro) for shiga toxin-producing escherichia coli o157:h7 (stec o157) in beef calves. Epidemiology and Infection. 132(2):291-295.

Interpretive Summary: Cattle are a major reservoir of Escherichia coli O157:H7, a bacterial serotype that has caused numerous foodborne outbreaks of severe, occasionally fatal, human disease. Knowledge of how E. coli O157:H7 is transmitted between cattle is important in order to devise rational on-farm infection control strategies. The basic reproduction ratio (Ro) is a term used to describe transmission of infectious agents in populations. It is roughly equivalent to the number of animals that become infected through contact with one infectious individual. This study was designed to estimate Ro for E. coli O157:H7 in beef cattle through the production cycle based on appearance of antibodies to O157 on the surface of the bacteria. Ro for E. coli O157:H7 infection in beef calves varied from 2.9 - 5.6 over 3 years, with an average of 4.3. Given the above estimate of Ro, it is predicted that 65 - 86% of a herd of calves must be effectively vaccinated, or must be rendered non-susceptible through other means, to eliminate E. coli O157:H7 infection from a herd.

Technical Abstract: To understand the dynamics of transmission of shiga toxin-producing Escherichia coli O157:H7 (STEC O157) in beef calves, serum samples were obtained from calves in a beef cow-calf herd approximately every 6 weeks from birth until weaning for 3 consecutive years. 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 ratio (Ro) was estimated for each of the 3 years as well as in aggregate using both deterministic and Martingale methods. Ro for STEC O157 infection in range beef calves by deterministic methods varied from 2.9 - 5.6, with an average of 4.3, CI95% 2.8 - 5.9. Martingale estimates of Ro ranged from 3.5 - 7.4, or 5.3, CI95% 3.9 - 6.6, for data from all three years. Given the above estimate of Ro, it is predicted that 65 - 86% of a herd of calves must be effectively vaccinated, or must be rendered non-suceptible through other means, to eliminate STEC O157 infection from a herd.