N. Field from the Animal and Bioscience Research Department, Teagasc, Moorepark Research Centre, Fermoy, Co. Cork, Ireland and colleagues have published an excellent Open Access article concerning Johne’s disease in the Irish Veterinary Journal. The article is succinct and comprehensive with 99 references cited. The pathogenesis of Johne’s disease is described briefly followed by an excellent summary comparing the accuracy of diagnostic tests for Johne’s disease both at the individual cow-level and herd-level using the latest research findings.
Johne’s disease is an infectious disease affecting cattle, other ruminants and non-ruminant wildlife worldwide, caused by Mycobacterium avium subspecies paratuberculosis (MAP). This review provides an up-to-date concise overview of the pathogenesis of MAP, the significance of Johne’s disease in cattle and the use of diagnostic testing at both animal and herd level in the context of seasonal pasture-based herds. While MAP can only replicate intracellularly, the bacterium is sufficiently robust to survive for months in the environment. Transmission of MAP is mostly via the faecal-oral route, however in-utero transmission in also possible. The bacteria evade the immune system by persisting in macrophages in the small intestine submucosa, with this latent stage of infection lasting, in most cases, for at least two years before bacterial shedding and clinical signs begin. The slowly progressive nature of MAP infection, poor performance of diagnostic tests and management systems that expose susceptible calves to infection make control of Johne’s disease challenging, particularly in seasonal calving herds. Testing of individual animals provides little assurance for farmers and vets due to the poor sensitivity and, in the case of ELISA, imperfect specificity of the available tests. Repeated herd-level testing is utilised by the IJCP to detect infected herds, identify high risk animals, and provide increasing confidence that test-negative herds are free of infection. The IJCP aims to control the spread of Johne’s disease in cattle in Ireland, in order to protect non-infected herds, limit the economic and animal health impact of the disease, improve calf health and reassure markets of Johne’s disease control in Ireland.
Ireland is the latest country to implement a national Johne’s disease control program and their scientists are concurrently generating research of practical importance to help drive the program. This publication is just one of many excellent products in recent years. Read more about the Irish program here.