A couple of years ago I was lucky enough to hear Peter Orpin speak about Johne’s disease in a cattle vet-farmer meeting. I thought this week it would be a good idea to revisit the disease and its causes.
Cause of Johne’s
M. paratuberculosis bacteria embeds itself in the wall of the ileum (lower part of the small intestine). As an immune response, infected tissues attempt to regenerate healthy tissue which leads to visible thickening of the intestines. This prevents nutrient absorption, resulting in weight loss.
Late in the infection, antibodies are produced and found in the serum (blood plasma without the proteins used in blood clotting) of animals and indicates clinical signs of disease – death will follow soon after this.
When the microbe is excreted, it can contaminate the soil or water. Outside the host animal, the organism multiplies poorly—if at all—but it can survive over a year in the environment because of its resistance to heat, cold, and drying.
The primary cause of the spread of Johne‘s disease is contact with the faeces or saliva of an infected animal.
Because of the slow, progressive nature of the infection, signs of Johne’s disease may not show up until years after initial infection.
- long-lasting diarrhoea
- weight loss despite good appetite
- Bottle jaw may also appear – fluid accumulation in the bottom jaw causing an abscess
Once clinical signs appear the animal will not recover and will continue to deteriorate.
There is no treatment for Johne’s but as always PREVENTION IS BETTER THAN CURE. It is much more cost effective to prevent than eradicate the disease once it has started spreading through the herd invisibly. The primary source of contamination is manure from an infected adult animal. It is very important to know the status of Johne’s in a herd when buying cattle as this is an easy way for Johne’s to enter a herd.
A vaccine has previously been made available in the US to prevent the risk of Johne’s which uses a mixture of killed mycobacteria and oil. It can sometimes cause large lumps at the site of injection. Occasionally these lumps will become draining abscess-like lesions. Although the vaccine is given to calves less than 30 days old, the tissue reaction at the injection site may last for life.
Another vaccine is available made from live M. paratuberculosis (but not disease causing).
The efficacy of vaccines is controversial. Studies in the Netherlands have shown that herd owners who follow the recommended management changes to control Johne’s disease could be just as successful as those who vaccinate.
Has anybody ever seen this disease before when seeing practice? Let me know in the comments!