Disease Information: Bovine Tuberculosis
What is Bovine Tuberculosis?
Bovine tuberculosis (bTB) is a serious infectious disease of cattle and a zoonosis (animal disease which can infect humans), caused by the bacterium Mycobacterium bovis (M. bovis). It can also infect and cause TB in badgers, deer, goats, pigs, camelids (llamas and alpacas), dogs and cats, as well as other mammals. The risk to humans is considered low.
Bovine TB is primarily a chronic respiratory disease for which there are often no symptoms until advanced stages of the disease. Symptoms in the later stages in cattle can include weakness, emaciation, appetite loss, fluctuating fever, respiratory problems and enlargement of the lymph nodes.
The incidence of bTB in Great Britain has been steadily increasing since the 1980s. There are now approximately 300 new herd incidents per month across Great Britain. It is particularly problematic in the west and south west of England and Wales.
How is it spread?
The disease is spread by contact with infected cattle or wildlife. It is transmitted by inhaling infected droplets or by ingesting the organism - for example, calves and humans could potentially become infected by drinking raw milk from infected cattle.
Biosecurity is of crucial importance in dealing with TB, both to protect uninfected herds, and to prevent infected herds from spreading the disease to uninfected herds or to wildlife.
Cattle can become infected by other cattle through direct (e.g. nose to nose) contact, or by sharing water sources or grazing on common land. Cattle movements present a particularly high risk, as contact with infected herds may occur through shared housing, at shows or markets, or through restocking of herds.
Although cattle are the natural hosts of M. bovis, wildlife can be very good maintenance hosts and are an important reservoir of the disease. In the UK, badgers on or around farms in endemic areas represent a major risk factor. An estimated one third of the badger population in endemic areas is infected with M. bovis. Although direct, or nose to nose, contact with cattle is likely to be extremely rare, the main risks come from badgers accessing feed stores. Securing feed stores, cattle housing and feed areas is very important. It is useful to remember that badgers can gain access through any gaps larger than 10cm.
For pastured cattle, there is a potential infection risk from badger urine and faeces concentrated around setts and latrines. It is recommended to fence off such areas.
There is compulsory surveillance testing for bTB in England and Wales. In areas with endemic bTB, or areas otherwise considered to be high risk, this is once per year. Throughout the rest of England, in low risk areas, four-yearly testing of breeding stock (routine herd testing) is carried out.
In TB breakdown herds short interval testing (not less than 60-day intervals) is required until one or two clear tests are achieved, depending on the risk status of the herd.
Bio-Genesys Diagnostic Tests
Bio-Genesys Ltd is developing a multi-antigen assay for TB, optimised for use in Cattle, Goats, Pigs and Wild Boar, Deer, Badger and Camelids (Llamas and Alpacas). Contact us for more information.