Evaluation of a milk ELISA as an alternative to a serum ELISA in the determination of the prevalence and incidence of brucellosis in dairy herds in Hubei Province, China.

This study was designed to compare a milk I-ELISA with a serum ELISA for the diagnosis of brucellosis in dairy cattle and then to use the milk I-ELISA to determine the prevalence and incidence of brucellosis in dairy herds in Hubei Province, China. The two tests were shown to have good agreement with a Cohen's kappa statistic of 0.747 (p < 0.001) when 147 animals originating from 4 dairy herds in the province were tested. The results of Bayesian Latent Class Analysis estimated that the sensitivity and specificity of the milk I-ELISA under field conditions were 87.2 % and 92.0 %, respectively. An epidemiological survey based on the milk I-ELISA was then conducted in 3091 cows from 15 commercial dairy herds from January to July 2018 in Hubei Province. The animal level real prevalence varied from 34.9 % (95 % CI: 28.5, 41.8) to 51.4 % (95 % CI: 48.2, 54.6) in the 15 herds tested. Most farms (93.3 %) tested contained at least one test-positive animal. As only ten farms met the inclusion criteria for the calculation of incidence risk, the overall real incidence risk in 10 of these farms was 0.4 % (95 % CI: 0.1, 1.2) per 3 months, which highlights the potential for spread of the disease within infected herds. It is concluded that the milk I-ELISA test could be used as a rapid screening test for brucellosis in unvaccinated dairy cows and, given the high occurrence of bovine brucellosis in this study, an effective prevention and control program needs to be developed and implemented in Hubei Province, China.