Michael Metzger, Michigan State University Extension Educator
(Previously published on MSU Extension, Sheep & Goat: January 3, 2019)
Johne’s is a serious disease that affects small ruminants.
Johne’s disease is a fatal gastrointestinal disease of sheep and goats and other ruminants (including cattle, elk, deer, and bison) that is caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP). Also known as paratuberculosis, this infection is contagious, which means it can spread in your flock or herd. Young animals are more susceptible to the disease than adults. It is primarily spread by the fecal-oral route but may also be transmitted across the placenta and through milk and colostrum of infected ewes and does. The most consistent clinical sign in sheep and goats is chronic weight loss despite a good appetite. Although profuse diarrhea is common in cattle with Johne’s disease, this sign is not common with goats or sheep. It is important to differentiate this disease from internal parasites because these conditions may look similar. This wasting condition eventually results in death, although infected animals may take months to years to show clinical signs of the disease. An infected animal can be shedding the organism in its feces, contaminating the environment and other animals in the herd. There is no cure for Johne’s disease.
The first diagnosis is often made at necropsy. Bacterial culture on live animals is not very successful in sheep. In goats, the bacteria can be cultured about 60% of the time when they are present in the feces. The bacteria are very slow growing and take 2 – 16 weeks to grow, meaning that negative results take at least 4 months and then a negative result may only mean failure to grow or that the animal is still in the early stages of disease. Blood tests can be used to detect antibodies to MAP. Blood tests rarely classify a healthy sheep or goat as infected (few false positives), but may misclassify many infected sheep and goats in the early stages of the disease and call them negative.
Eradication of Johne’s disease from a herd or flock can be time consuming and difficult. Michigan State University Extension recommends the following to prevent the disease from entering your herd or flock:
- Maintain a closed herd. Don’t buy Johne’s disease.
- Purchase animals only from herds or flocks that have tested for Johne’s disease.
- If no diagnostic testing has been conducted in the source herd or flock, at least closely evaluate the body condition of all the adult animals
- If the animal to be purchased is less than a year old, test its dam since infected young animals are unlikely to test positive for the infection.
- Do not bring in other species that are susceptible to Johne’s disease: cattle or other ruminants.
- Do not board or borrow other people’s animals, as this can introduce the infection into your herd or flock.
Due to lack of testing and reporting, it is not known how widespread Johne’s disease is in sheep and goats in the United States. However, the disease had been confirmed in many goat herds and sheep flocks throughout the country.