Ovine strain of Mycobacterium paratuberculosis in beef cattle: A case study #2

Summary

Johne's disease (JD) is a chronic gastrointestinal wasting disease of some importance in cattle and sheep populations, caused by Mycobacterium avium subsp. paratuberculosis (Mptb), which can survive in the environment for months. There are distinct strains of Mptb; a cattle (C) strain that affects predominantly cattle (but is also capable of infecting goats, deer and alpaca), and a sheep (S) strain predominantly affecting sheep.
Retrospectively, S strain Mptb has been diagnosed in cattle on at least eight New South Wales (NSW) properties, and in 1999 and 2005 cattle with clinical signs were diagnosed with S strain Mptb in Victoria. These properties had known ovine Johne's disease (OJD) infection in sheep. This study was undertaken following the diagnosis of S strain Mptb infection a seven year old cow in a MN2 stud beef herd in the Ballarat region of Victoria that had been managed in accordance with the National Market Assurance Program for Cattle (CattleMAP)  on a property without sheep.
The Australian Johne's Disease Market Assurance Program, an audited quality assurance program incorporates animal health risk assessment, testing and movement control that provides low risk animals for the various industry sectors. To determine the within herd distribution of S strain Mptb, to improve understanding of S strain Mptb infection, and to examine possible risk factors for disease transmission, the remaining 55 head of cattle were slaughtered and samples collected and examined for S strain Mptb. The index case was the only animal found to be infected in the herd, and the route of infection could not be determined given the results.  There was no evidence of within herd spread of infection, which is more significant as time increases since initial infection of the index case.