VARIATIONS IN SEROPREVALENCE AND HOST FACTORS FOR BOVINE ANAPLASMOSISIN ILLINOIS

The modified card agglutination test (MCAT) was used to detect antibod ies to Anaplasma marginale in 4994 samples collected from market cattl e through the Brucellosis Eradication Program in Illinois, The MCAT re actor rate in the sample was 6.4%. The statewide prevalence estimate i ncreased to between 7.1% and 10.7% when corrected for sampling distrib ution and test sensitivity and specificity. While the sample reactor r ate measures the proportion of infected cattle moving through the mark et system and into new herds, consideration of the sampling proportion s and test characteristics is important when estimating the overall pr evalence. Cows were found to be at decreased risk relative to male cat tle in lower-prevalence areas, but the risk was similar in higher-prev alence areas. In both higher- and lower-prevalence areas, the risk for seropositivity increased from 1 year of age onwards, but the rate of increase with age was greater in the higher-prevalence areas. Calves, however, had higher seroprevalence levels than 1-2-year-old animals. T he risk was highest for Angus and Angus-Hereford cross cattle, while d airy cattle showed a decreased risk in the whole sample, but not when the analyses were stratified by prevalence level. There was a higher c oncentration of dairy cattle in areas with lower prevalence levels.