Johne's disease - Overview
Johne’s disease is a common but often misunderstood condition in New Zealand livestock. It’s a chronic, incurable intestinal disease that affects sheep, goats, cattle, deer, llamas and alpacas. Goats and deer are particularly susceptible, and the infection is more widespread than many lifestyle farmers realise.
This is the first article in a three-part series. Parts 2 and 3 will focus on Johne’s disease in sheep and goats, and in cattle and deer, respectively. Here, we look at what Johne’s disease is, how it spreads, and why it matters.
What is Johne’s Disease?
Johne’s (pronounced “yoh-neez”) is caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP). It slowly damages the intestinal wall, leading to poor nutrient absorption. The disease is progressive and always fatal once clinical signs appear.
Typical symptoms include:
Gradual weight loss and declining body condition
Chronic diarrhoea, particularly in cattle, goats and deer
Poor response to treatment
Eventual death, usually within weeks or months of signs appearing
Infection typically occurs when animals are very young. In cattle and sheep, signs usually show between three and five years of age. In goats and deer, symptoms can begin as early as eight months.
How Common is It?
Johne’s disease is more common than most people realise. Many New Zealand farms have infected animals without obvious clinical signs. The disease may be quietly reducing production long before it is diagnosed. Because symptoms can take years to appear, the problem is often more widespread than it seems.
Signs to Watch For
Cattle often develop weight loss and chronic diarrhoea in mid-life
Sheep are affected similarly but may not scour
Goats and deer can develop symptoms much earlier, with rapid decline
Only a few animals may show signs at any one time, even in an infected herd or flock
How the Disease Spreads
The disease spreads through contaminated faeces, colostrum, milk and the environment. Infection is most likely in the first few weeks or months of life. Young animals may also be exposed through faecal contamination on the udder during suckling or, less commonly, in utero. MAP bacteria can survive for many months in soil and water.
Other Causes of Similar Symptoms
Before assuming Johne’s disease is to blame, rule out common causes of weight loss and diarrhoea, such as internal parasites or other infections. If worm treatments do not help, consult your vet.
Prevention and Control
There is no effective treatment for Johne’s disease. Once symptoms appear, the disease is always fatal. However, there are ways to reduce the risk:
Vaccination is available for sheep and goats. It should be administered in the first few months of life. While it may not prevent infection, it reduces the likelihood of clinical disease.
Vaccination is not permitted in cattle and deer, because it can interfere with tuberculosis testing.
Good management and biosecurity help control the spread.
In herds or flocks with known infection, testing and culling of affected animals may be advised.
