You might well have heard of Johne’s disease, because it’s a common problem in ruminants. But even if you’ve heard of it, you may not know much about it. It’s a complex disease, often misunderstood and easily misdiagnosed.
- Johne’s disease can cause disease and death in sheep, goats, cattle and deer.
- It can also affect llamas and alpacas (camelids).
- Goats and deer are particularly susceptible.
- It’s much more common than you might think.
This is the first of a series of three articles in which we explain what Johne’s disease is, how you can tell if you have any affected livestock and what to do about it if you have.
In this first article we present some background information about the disease in general.
What is Johne’s disease?
- Johne’s (pronounced “yoh-neez”) disease is a chronic (long-standing) disease of the intestine.
- It causes reduced weight gain, and steady loss of body condition and body weight leading to emaciation.
- It often causes scouring, especially in cattle, deer and goats.
- It is incurable. Once signs appear death is inevitable within weeks or months..
- Treatments have no lasting effect on the course of the disease.
- Usually, infection occurs when the animals are very young.
- Infection lies latent and may flare up to cause obvious disease later in life.
- In cattle and sheep the signs of disease usually develop when the animals are middle-aged and the disease progresses over a period of months or years.
- In goats and deer, the signs can appear from about 8 months of age and they can develop quickly, causing death within weeks.
Why is it important?
- Johne’s disease is relatively common in ruminants on New Zealand farms. For example, a recent survey of deer farms showed that there are infected deer on over 50% of farms although on many farms it doesn’t cause obvious disease.
- It is incurable.
- It causes weight loss, diarrhoea and deaths in a proportion of the animals in the herd or flock.
- It is costly. There are the costs of attempted treatments, vet bills, the deaths of animals …. and the owners’ distress!
- Goats and sheep can be vaccinated against Johne’s disease but vaccination is currently not an option for cattle and deer because it can cause false positive reactions to the Tb skin test.
What are the signs?
- Cattle develop diarrhoea and weight loss when they are 3 to 5 years old, leading to death usually within a few months. Usually only one or two cattle on a farm are obviously affected at any one time.
- Goats from 8 months of age develop diarrhoea and weight loss that leads to death usually within a few weeks.
- Sheep are like cattle, and they develop the disease at about 3 to 5 years of age, but diarrhoea is not always present.
- Deer are like goats. Usually no more than a few adult deer are obviously affected at any one time, but outbreaks can develop in yearling deer causing wasting and deaths in up to 25% of the mob.
What causes it?
- The cause is a bacterium, Mycobacterium paratuberculosis.
- Mycobacterium paratuberculosis is closely related to the bacterium that causes tuberculosis in cattle and deer (Mycobacterium bovis).
Do all infected animals show obvious signs of disease?
- No, and this is one of the most dangerous things about the disease.
- For every animal that develops the scouring and weight loss signs, there are very many more that are infected and possibly excreting the bacteria but still apparently healthy.
What else can cause these signs?
- Heavy worm burdens can cause diarrhoea and weight loss.
- Other chronic diseases (infections, tumours) can cause steady weight loss.
- Before assuming that an animal that is losing weight and scouring has Johne’s disease, it’s important to test for worms.
- If worm treatments have no effect, consult a vet
How does the disease spread?
- Bacteria are shed in the faeces of infected animals, whether they have diarrhoea or not.
- The disease can spread from mother to young in the womb, and via her milk or as a result of faecal contamination of her udder when the baby suckles.
- An important feature of the disease is that animals are most susceptible to infection when they are young. It is likely that most infections occur in the first few weeks or months of life.
Can Johne’s disease be prevented or treated?
- No. Treatments have no effect on the progression of the disease although they may cause the diarrhoea to dry up for a short time.
- Fortunately, there is a vaccine that can help protect against Johne’s disease, and sheep and goats can be vaccinated against it.
- The vaccine doesn’t necessarily prevent infection but it does prevent obvious signs of the disease from developing.
- The vaccine should be given in the first few months of life.
- Currently, cattle and deer must not be vaccinated because vaccination can cause false positive reactions to the Tb skin test.