Johne's Disease and Bovine Tuberculosis: Chronic Disease Tests

Johne's disease and bovine tuberculosis are slow illnesses of cattle and buffalo that cause weight loss over months or years. Lab tests can look for antibodies or for the germ itself, but both are hard to catch in a single sample, so one negative result never clears a herd. Tuberculosis can also pass to people.

What is Johne's disease?

Johne's disease (paratuberculosis) is a long-lasting infection of the gut caused by a bacterium called Mycobacterium avium subspecies paratuberculosis, or MAP. Animals usually pick it up when young, from the faeces, milk or colostrum of an infected adult, and show no signs for years. Later the animal may lose weight in spite of a good appetite, give less milk and develop persistent watery diarrhoea. Swelling under the jaw can appear. An infected animal stays infected, and she sheds the germ in her dung, often long before she looks ill.

What is bovine tuberculosis?

Bovine tuberculosis is caused by Mycobacterium bovis. It is also slow. An infected animal may have a long cough, lose weight, have swollen lymph glands and tire easily, or may look quite normal for a long time. The germ can pass to people who live and work close to infected animals, so owners, milkers and vets should take care. If you have a cough that lasts for weeks and you work with animals, tell your doctor.

Which lab tests are used?

For Johne's disease:

• the Johne's Disease (Paratuberculosis) Antibody ELISA looks for antibodies in blood or milk
• the Johne's Disease (MAP) RT-PCR - Faeces is an RT-PCR (real-time PCR) test that looks for the genetic material of the germ in dung, so it can find animals that are shedding it

For tuberculosis:

• the Bovine Tuberculosis Antibody (ELISA) looks for antibodies in blood
• the Bovine Tuberculosis (Mycobacterium bovis) RT-PCR looks for the germ in suitable samples

Skin testing of cattle for tuberculosis is a separate method that a vet performs on the animal itself, and the lab does not do it. The lab confirms the method and the sample needs when you book.

Why can one negative result be wrong?

These germs hide. In Johne's disease an animal sheds the bacteria on and off, so one dung sample can be negative on a day that she is not shedding. Antibodies may not have appeared yet in a young or recently infected animal. In tuberculosis, antibody tests may miss early cases. A negative result lowers the chance of disease but does not rule it out, and one negative result never clears a herd. A registered veterinarian reads all the results together with the animals' signs and history, and may suggest repeating the tests after some time or testing more animals.

Which animals should be tested?

Vets usually start with animals that have long-term weight loss, diarrhoea that does not settle or a lasting cough. In a herd with a known case, they may test the others, and animals that are bought in are often tested before joining. Testing every animal each time is rarely practical, so the vet will plan.

Blood is drawn from a vein into the tube the lab names, and dung should be fresh, in a clean lidded container. Use gloves, wash your hands well afterwards and keep all samples sealed in bags, away from food. Label each with the animal's number and the date, and phone the lab first.

What should owners do about the herd?

Ask your vet how to keep young calves away from the dung and milk of older animals, which is one way Johne's disease spreads. Do not sell animals that you suspect of carrying a notifiable disease without talking to the vet. The lab gives no treatment advice and no promise about herd control.

Read next

Trace minerals also affect condition and growth, as described in Copper, Zinc and Selenium: Trace Mineral Tests for Dairy Herds. To understand how germs are grown and tested, see Culture and Sensitivity: What It Tells Your Vet.

Testing in Bhopal

Your vet usually takes the samples, and the lab at C-200, C Sector, Shahpura, Bhopal accepts them. Collection is free anywhere in Bhopal, and other districts can use courier, bus parcel or their vet. Call or WhatsApp +91 88175 01118; the lab confirms the method, sample needs and reporting time when you book.