MODELING THE EFFICACY AND EFFECTIVENESS OF ESCHERICHIA COLI O157:H7 PRE-HARVEST INTERVENTIONS

Authors

Amanda R. Vogstad, University of Nebraska - LincolnFollow

Date of this Version

Spring 5-2012

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Veterinary Science, Under the Supervision of Professor David R. Smith. Lincoln, Nebraska: May, 2012
Copyright 2012 Amanda R. Vogstad

Abstract

Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) is one of the leading causes of hemolytic uremic syndrome in humans. Reducing the prevalence of STEC O157 in live cattle may reduce ground beef prevalence and subsequent human illness. Type III secreted protein vaccines (TTSP) reduce fecal shedding of STEC O157 in cattle. However, pre-harvest vaccines have yet to be adopted by the beef industry. The objectives of this thesis were to 1) conduct a meta-analysis to test factors effecting efficacy of a 3-dose regimen TTSP vaccine product, and 2) use stochastic simulation to model the usefulness of preharvest control measures. In the meta-analysis, data was used from four randomized controlled vaccine trials conducted from 2002-2008 at the University of Nebraska–Lincoln (n=184 pens, 1,462 cattle). Results indicated, study, challenge load, and days from administration of the last dose of the vaccine did not modify the measure of vaccine efficacy for a 3-dose regimen TTSP vaccine product. Model adjusted efficacy was 48% (95%CI, 0.37-0.57). In the modeling study, we simulated the pen-level fecal shedding prevalence distribution of cattle fed in the summertime and vaccinated with a TTSP vaccine and compared it to the winter fecal shedding prevalence distribution. Model inputs were previously observed frequency distributions for number of animals within a pen, and pen-level fecal shedding prevalence for summer and winter. Uncertainty about vaccine efficacy was modeled as a log-normal distribution (μ=58, SE=0.1393). The simulation was performed 5,000 times. Vaccination with a TTSP vaccine reduced summertime pen prevalence distributions of STEC O157 to levels comparable to wintertime pen prevalence, with the major effect being reduced variability in fecal shedding prevalence. Our simulation model should be a useful tool for food safety decision makers evaluating the usefulness of pre-harvest interventions.