DISEASE RISK MANAGEMENT: BOVINE TB - THE FACTS PART 1
Mycobacterium bovis, is a slow-growing (16- to 20-hour generation time), aerobic bacterium and the causative agent of tuberculosis in cattle (known as Bovine TB). Related to M. tuberculosis—the bacterium which causes tuberculosis in humans—M. bovis can also jump the species barrier and cause tuberculosis in humans and other mammals.
For thousands of years the extremely contagious Bovine TB has presented a perilous threat to mostly any vertebrate animal due it being so contagious. First recordings of this disease in South Africa were noted in cattle in the eighteenth century and thought to have been introduced through the importing of affected animals. This disease is now mainly widespread in developing countries such as Africa, parts of Asia and the Middle East.
This disease enters the body orally, damaged or cracked skin or open sores and through breathing the bacterium in via the mouth. The incubation period between being infected and symptom development generally occurs over a number of months. Animals may also be infected with this disease for a number of years but only present symptoms when they are highly stressed or when they reach old age.
How Bovine TB is Spread
Direct Transmission
The direct contracting of Bovine TB generally occurs in close or confined spaces. An infected animal will cough out small droplets of infected mucous which is transferred to other animals in the immediate vicinity when they breathe this air in. The bacterium can all adhere to dust particles and be transported via the air where it can again be inhaled by other animals.
Oral Transmission
The oral contracting of Bovine TB often occurs when animals drink infected milk or water. This type of infection also occurs when grasslands or feed bins have been contaminated with the bacteria when the mucous of an infected animal has been coughed up and contaminated the food which another animal then consumes. This disease may also be transmitted by saliva or food particles where contaminated lesions in the digestive system or tract are present and bacteria is excreted in dung, as well as by milk, urine or sheath secretions, should the specific organ be affected. Affected lymph nodes that excrete externally may also infect food or water sources.
Bovine TB is can also be transmitted iatrogenically through contaminated needles, speculums and other livestock apparatus as well as during mating if the genitals of either animal are infected. Transmission of this disease via open wounds or from an infected cow to her calf in the uterus is also possible.
Bovine TB bacterium remains infective outside of the body is mostly dependant on climatic conditions; heat, drought and direct sunlight are unfavourable to these bacteria which thrive in a dark and moist environment. If not exposed to sunlight and in temperatures of between (12 – 24* Celsius) Bovine TB bacteria can survive for up to seven days, in stagnate drinking water for up to eighteen days and in moist dung for up to eight weeks.
Bovine TB Infection
Once this disease enters the body infection occurs when the bacteria encourage the formation of tumour like lesions referred to as tubercles which are light orange in colour. These tubercles usually develop in the lymph nodes which are generally examined first to detect infection.
If the bacteria spread to other parts of the body via the bloodstream or lymphatic system new tubercles will develop. If the bloodstream contains numerous bacterium toxaemia may occur which may lead to weakness, lack of energy and eventual death in the animal.
Sporadically the tubercles will be adequately encapsulated by connective tissue which will inhibit further spread through the body, controlling this disease.
To Be Continued
