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Bovine tuberculosis, more commonly known as bovine TB is a notifiable disease in the United Kingdom and all cases must be reported to the local authority. This disease is highly contagious and infectious. The majority of warm blooded animals are able to host the disease including cattle, sheep, horses, foxes, badgers, dogs and cats. Most have the same signs and symptoms as those seen in cows although the feline family experience further symptoms. Due to the contagious nature of the disease, cows found to be infected have to be culled by law.

 

 

Bovine tuberculosis

The disease bovine tuberculosis is a bacterial infection caused by a bacterium known as Mycobacterium bovis (M.bovis). Tuberculosis is an infection of the respiratory system. In some cases the bacteria has time to travel to the lungs of the animal or even the digestive system.

Cattle found to be more susceptible to the bacteria are considered to be the younger population although all cattle can become infected. The bacteria are usually transmitted via aerosol droplets. This usually occurs when an unaffected animal inhales contaminated droplets expelled by an infected animal through coughing and sneezing. The signs and symptoms observed include coughing, laboured breathing, and weight loss.

 

The disease is zoonotic. This means the bacteria can be transmitted to humans. This transmission can occur via aerosol droplets but the most well-known method is by drinking unpasteurised milk contaminated by an infected cow.  Pasteurising milk is said to destroy any M. bovis bacteria present. It has been suggested that the disease can also be transmitted by the ingestion of contaminated meat which has not been adequately cooked. There are no vaccines available for bovine tuberculosis.

 

Transmission of bovine TB

Bovine tuberculosis is transferred via the inhalation of aerosol droplets have been exhaled, sneezed or coughed from an infected cow. Other bodily fluids such as milk and colostrum, saliva, urine, and faeces are also able to act as sources of infection. Contaminated water troughs can result in the transmission of bovine TB. Contact between the open wounds of infected and unaffected cattle is also able to transfer the disease. The bacteria can also be ingested.

 

Animals kept in crowded conditions transfer the bacteria extremely rapidly throughout the herd. Such animals include dairy cattle and intensively farmed beef. Moving cattle across the country between farms contributes to the widespread nature of the spread of the bacteria. Other animals are also able to spread the diseases. Badgers and deer are able to catch the disease, become carriers, and potentially transmit the infection to cattle. Malnourished and stressed animals are highly susceptible when compared with the contrary. Once one cow becomes infected, each member of the herd is likely to contract the TB. Cattle are also more at risk if they graze on common land.

 

Humans are susceptible to catching the disease in the same way as cows although infected aerosol droplets from cattle rarely infect humans. They can also become infected if unpasteurised or incorrectly pasteurised milk is drunk. Additionally, humans can transfer the disease between each other. Currently the incidence of human infection is relatively low and seen to be quite rare.

 

The bovine tuberculosis bacteria are able to survive for long periods of time outside its host, where there is a lack of direct sunlight. In favourable conditions where it is warm and moist, M. bovis can still infect cows. In addition, it can survive in faeces and water sources. 

 

Signs and Symptoms of Bovine tuberculosis

Initially, cows do not show any signs or symptoms following infection. These cows are called asymptomatic and, prior to testing, farmers usually remain unaware of the outbreak during this stage. It can take as long as a few years before any signs can be observed.

 

As the infection progresses in cattle, bovine tuberculosis causes a slight fever and the lymph nodes usually swell or have abscesses. The cow will appear weak, cough and show signs of laboured breathing and have an increased breathing rate. A loss of appetite will be noticed and the decrease in weight may be so significant that the cow actually becomes emancipated.

 

When the digestive system is affected diarrhoea or constipation may result. The enlargement of the lymph nodes may restrict breathing around the respiratory trachea. In especially severe, cases pneumonia develops and if the cow is not culled then this will usually result in death.

 

Treatment of Bovine tuberculosis

Bovine TB is extremely difficult to treat and animals are culled rather than having any treatment even attempted. If the cow is treated, it can take as long as nine months and involves using various antibiotics at different intervals as a result of its resistant nature. This can be a highly expensive option when dealing with an infected cow. In the United Kingdom infected cows must be destroyed.

 

Prevention of Bovine TB

Vaccines are not yet available to protect cattle against bovine tuberculosis. Preventative measures are essential in the prevention of this disease. Wildlife such as badgers should have reduced contact with cattle and so double fencing  to prevent the cows nearing the badgers while still leaving the badgers free to roam may be necessary. Areas storing feed should be protected against contact with wildlife as they could spread the disease.

 

Cows put out to pasture on closed, non-mixed fields are thought to be safer than shared grazing on common land. New cattle brought in should be tested and proven to not have any TB present in their system. It is also recommended that they be isolated and observed for a period of time prior to being introduced to the herd. Regular tests are made to control the incidence in the area. Cattle that have tested positive are culled. This prevents the bacteria from being transmitted to other members of the herd or even spreading the infection to other farms. Pasteurisation of milk destroys the bacteria since it cannot survive in high temperatures. Any cows suspected or proven to have TB should be reported to the local authorities immediately.

 

Diagnosis of bovine diagnosis

Skins tests are routinely used in cattle. They are also done before the animal is transported for example from farm to farm.  If an animal reacts by swelling once injected then this is a positive test and it is culled.

 

Prognosis of bovine tuberculosis

Due to the fact that bovine tuberculosis is a highly contagious disease and is known to rapidly infect members of the herd, infected animals are culled to prevent the spread of infection in the UK. This is also because it poses to a threat to other animals in the area since wildlife and other animals are able to acts as sources of infections.

 

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