Bovine tuberculosis (Mycobacterium bovis) is a bacterial disease that affects the lungs. It is contagious and chronic once it is established. It usually affects cattle but can be spread to any warm-blooded mammal, even humans. This type of tuberculosis is very similar to human tuberculosis. Symptoms often don't appear until the disease has reached an advanced state. This disease can be found worldwide, although many countries, especially in Europe, are now declared tuberculosis free.
Early stages of bovine tuberculosis usually have no detectable symptoms, and it may take several months before the first symptom is detected. Infections may also remain dormant for several years, only to activate when the animal is stressed or suffering from old age. The first sign noted may be a moist-sounding cough that quickly becomes chronic after the bacteria has got a firm hold in the animal's lungs. This may progress into pneumonia. A low-grade fever may also be present. Although the infection is most common in the lungs, it may also affect the brain, the kidneys or the spine. Early infections may be caught through regular testing in places where eradication programs are found. When infected cattle are found, the entire herd is put down. The farm is then disinfected and must remain free of infection for at least thirty days before cattle can once again be introduced.
As the disease progresses, the animal may become thin due to lack of appetite. The cough worsens, especially in cold weather or when the animal exercises. They become lethargic and weak. Once the animal is in the terminal stage, they may show severe respiratory distress. A veterinarian may notice enlarged lymph nodes, and in severe cases, the lymph nodes may rupture and drain. Enlarged nodes may also block blood vessels or airways, causing great distress to the animal. If the digestive tract is involved, the cattle may show signs of constipation or diarrhoea. Through eradication programs, few cattle reach the severe stages of the disease.
Cattle that have died or are found at the slaughterhouse will have the telltale lesions in the lymph nodes and lungs. Some of these tiny abscesses can only be seen under close inspection during a necropsy. Lesions may also be found rarely on the genitalia.