What are the stages of Johne’s disease infection in cattle?
Johne’s disease has three stages. Stage I is a silent, subclinical and non-detectable infection seen typically in calves, heifers and young stock less than two years of age and in adult animals exposed to small doses of disease-carrying organism. Infected animals at this early stage are rarely detected with currently available diagnostic tests, including fecal culture or serologic tests (ELISA). This stage progresses slowly over many months or years to Stage II. Stage II is subclinical infection that typically occurs in older heifers or adults. Animals at this stage appear healthy but are shedding adequate numbers of M. paratuberculosis organisms in their manure to be detected on fecal culture. Blood tests will detect some animals but not all animals at this stage. Blood test (ELISA) positive animals should be confirmed positive by fecal culture. These animals pose a major but often hidden threat for infection of other animals through contamination of the environment. Stage III is clin
