What is Johne's?
Johne's disease is a chronic, progressive intestinal disease caused by infection with Mycobacterium avium subspecies paratuberculosis (Map). For an order form please click here.
The disease has a long subclinical phase, during which animals can spread the infection without themselves exhibiting signs of illness. Infection causes abnormal thickening of the lining of the intestinal tract in infected animals restricting the absorption of nutrients. Clinical signs of animals infected with Johne's are long lasting diarrhoea and extreme weight loss despite the animal having a good appetite (cattle over 18 months).
Animals are usually infected when young with calves being 80% more susceptible in their first month of life. The calf may be infected while in the womb, by drinking infected colostrum and milk, or by ingesting faeces. The organism may last for a year in slurry or on pastures. An infected cow can shed billions of organisms into the environment for years prior to showing any clinical signs of the disease. Only 1-5% of infected cows in a herd will show clinical signs of the disease. The rest of the infected animals will appear healthy, highlighting the need for testing. Infection is almost always introduced to a herd by purchasing infected replacement breeding stock including bulls.
Testing is carried out using a milk or blood ELISA to test for antibodies. Single antibody tests are unreliable for confirming infection but can merely give an indication as to an animal’s status. This combined with the sporadic nature of the animal’s antibody response makes it a challenging disease to detect and respond to. IML recommends repeat testing of animals to confirm status before management decisions are made.