Johne's disease in Angora goats
By Dr Mackie Hobson BSc(Agric),BVSc

1. Diseases

Johne’s is caused by Mycobacterium avium paratuberculosis (MAP) and any ruminant species is susceptible. Johne’s can therefore potentially be a threat to the Angora goat. The disease has however not been diagnosed in Angora goats in South Africa and it is primarily a sheep health problem.

Due to the slow incubation period it is difficult to determine the spread of the disease across the country. Johne’s is a controlled disease (Act 35 1984) but legislation and what is currently actually happening at farm level are very different. The law stipulates that if a positive case is identified the farm is placed under quarantine and control measure implemented.

Clinical signs of Johne’s disease:

• Rapid weight loss
• Diarrhoea (less common in goats)

The infection occurs in kids in the first months of life, but signs of disease usually do not appear until the animals are adults.

• The goat eats well but adults become thin and weak.

Why does a goat that has been infected for years suddenly become sick?

This is due to the slow incubation period. The intestinal (ileum) MAP that has been in the cells for months or years suddenly starts to replicate and take over more of the intestinal cells. The goat’s immune system then mounts an inflammatory response which causes thickening of the intestinal wall. This thickening of the intestinal wall reduces absorption resulting in weight loss and diarrhoea.

How can goats get infected?

Goats (kids are more susceptible) may become infected without the farmer knowing. Johne's disease may potentially enter a flock when new sheep or goats are introduced. The infected animal sheds the organism through its faeces into the environment which can then be taken up orally by the goat. It is possible that kids become infected before birth through the uterus. The infection may survive for months in the environment (water 270 days, 264 days in cattle dung). There is a correlation between soil types and Johne’s disease with the disease being less common in alkaline soils.

How do you test goats for Johne's disease?

Tests are not perfect. The three common ways to test a herd for Johne's disease are:

1. Culture of faecal samples (individual or pooled) to isolate MAP,
2. PCR with the same faecal samples to detect MAP DNA.
3. Blood tests for antibodies

Diagnosis of a flock is easier than an individual animal

What are the post mortem signs?

• Thickening of the intestine (ileum) mucosa
• Thickening of the lymphatics on the serosal surface of the ileum and caecum
• Enlargement of the mesenteric lymph nodes

Histopathology samples: ileum and mesenteric lymph nodes.

Can Johne's disease be cured with antibiotics?

No.  Symptoms may be reduced but will relapse after treatment.

Can you vaccinate against Johne’s?

Vaccination does not provide 100% protection; vaccinated animals can still remain carriers although the risk of infection will be reduced.

Vaccination can only be done on prescription from a state vet.

Vaccinated animals will test positive for Johne’s and currently it is not possible to distinguish vaccinated animals from infected animals.

The vaccine can only be used in infected flocks and vaccinated animals need permanent identification.

Can humans get Johne's disease?

There is a human disease called “Crohn's disease” that is similar to Johne's disease. Crohn’s disease is a chronic inflammatory bowel disease (IBD) that has no known cause and no known cure. Some researchers believe MAP contributes to Crohn's disease. No connection, as yet, has been shown between contact with animals or the produce from these animals.

References:

Bath G & de Wet J. 2000. Sheep and goat diseases.

NSW Department of Primary Industries / Agriculture. OJD: The Vaccine.