Factoid - Bovine Tuberculosis

Key diagnostic tags
TB, Chronic, Respiratory, Zoonosis

Risk to human health: HIGH

Overview

Bovine Tuberculosis (TB) is a chronic bacterial disease of humans and animals, and is present in many species of animal including cattle, pigs and sheep. The disease is mainly spread between animals via inhalation or respiratory fluids, and the disease causes the formation of multiple masses called tubercles, particularly in the lung and lymph nodes. Many other organs can be affected by the tubercles, which are usually dry and firm, and have a tough fibrous capsule containing a soft, thick, pus like fluid inside. Tubercles can range in size from being too small to see without a microscope, to involving a large part of an organ. Link to pictures

Humans - Bovine TB represents a serious risk to public health, particularly farm and slaughterhouse workers. Most human infections are from drinking contaminated unpasteurised milk. AIDS/HIV patients are at particular risk from bovine TB. Link

Signs

The disease is a slow process, so initially there may be no visible signs in affected cattle. Clinical signs can develop when the disease is more advanced, and can include coughing, wasting, enlarged lymph nodes, weakness, difficulty breathing, and loss of appetite.

Humans - It can be years after infection when signs appear and can include lymph node enlargement in the neck, intestinal disease, or long term skin lesions. Humans can also acquire the disease from the spray of coughing infected cattle and can develop lung disease as a result. There are also other forms of TB which humans can acquire other than Bovine TB. Link

Diagnosis

The primary method of diagnosis is the Delayed hypersensitivity test, which involves the injection of tuberculin into the skin of the animal. Swelling in the skin in response to this injection 72hours later indicates a potentially infected animal (this can be used in conjunction with an avian TB injection known as a comparative test). A blood test (gamma interferon assay) can also be used to aid diagnosis. After death, the presence of tubercles can be diagnostic but care should be taken as there is a potential for human infection. Further information

Humans - There are a range of tests available including the use of imaging machines to demonstrate the presence of clinical disease, as well as blood tests (Mantoux test, and the gamma interferon assay) for disease that has not yet become clinical. If the patient has had a BCG vaccine the Mantoux test may show a mild positive and does not mean the patient has TB. Further information

Treatment and prevention

The treatment of Tuberculosis in animals is not recommended as it is infectious to other animals and would take a long time to treat. Control of the disease should be based on testing potentially infected animals and slaughtering those that show a positive result. Control in a group of animals can be difficult and take a long time to achieve; especially if other cattle in the herd are being exposed to the disease from other sources (i.e. test and slaughter will have little impact if the herd is being frequently mixed with potentially infected animals.)

Prevention is aimed at preventing the herd having contact with other infected animals (i.e. infected cattle from other herds, or infected wildlife)

Humans - Extremely long courses of antibiotics (including combinations of isoniazid, rifampicin, pyrazinamide and ethambutol for up to 6-12months) are used in cases of both lung TB and TB affecting other organs. Patients with HIV/AIDS that have non-clinical infection should also seek treatment. Further information

Diseases with similar signs

Any long term respiratory disease (i.e. pneumonia)

Any wasting or chronic disease (i.e. Johnes disease)

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