An epidemiological study of paratuberculosis in dairy cattle in Ontario: study design and prevalence estimates.

An observational study involving 304 dairy herds and three abattoirs was conducted between 1986 and 1989 to investigate the epidemiology of paratuberculosis in dairy cattle in Ontario. The objectives of this paper were to describe the method of data collection for the study, to present descriptive production statistics and to present estimates of the prevalence of paratuberculosis among dairy cattle in Ontario. Mycobacterium paratuberculosis was isolated from the distal ileum and/or the ileocecal lymph node of 5.5% of 400 cull cows. Based on a lipoarabinomannan antigen enzyme-linked immunosorbent assay (LAM-ELISA) on sera, the predicted true prevalence of paratuberculosis among 14,923 dairy cattle from 304 herds, was 6.1%. Nineteen percent of 2,943 fecal cultures were uninterpretable because of overgrowth with contaminating bacteria or fungi. It was concluded that the true prevalence of paratuberculosis among dairy cattle in Ontario was no greater, and may be less than the true prevalence among dairy cattle from various regions of the United States. However, at a practical level, for the purposes of trade policy, the present study suggests that the functional prevalence is very similar in the two countries.