Avian tuberculosis

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Avian tuberculosis is a slowly spreading, chronic bacterial infection. All bird species appear to be susceptible, although to variable degrees; pheasants seem to be highly susceptible, while the disease is uncommon in turkeys. The disease is more common in captive than wild birds and is uncommon in commercial poultry flocks due to the short life span and husbandry practices. Tuberculosis has been found in emus and other ratites. Avian tuberculosis also cross-infects other animal species, such as pigs, sheep, rabbits, rodents and calves. The bacterium can be carried asymptomatically by adult cattle and has been isolated from people with acquired immunodeficiency syndrome.

Symptoms do not usually develop until late in the infection. The disease in birds is characterised by gradual weight loss, sluggishness and sometimes lameness. Combs and wattles shrink and become pale. Affected birds are usually more than a year old. The disease causes multiple granulomas (a small mass of firm tissue formed as a result of inflammation) to form in a number of organs, predominantly in the liver, spleen, intestine and bone marrow.

What causes avian tuberculosis?

Avian tuberculosis is caused by the bacterium Mycobacterium avium. This bacterium is closely related to the human and bovine TB bacteria. It can survive for as long as four years in the soil or when protected by organic matter. It is also resistant to acid and alkali. Infected birds with advanced granulomas excrete the bacteria in their faeces. Infected dead birds and offal may infect penmates, rodents and predators if eaten. The bacterium can spread from bird to bird, animal to bird and bird to animal. The incubation period is several weeks to months.

Prevention and treatment of avian tuberculosis

There is not treatment for avian tuberculosis. Control is achieved through depopulation and good biosecurity practices including rodent control, screening against wild birds, isolation from other birds and animals and good sanitation. Dirt-floored houses should have several inches of the floor removed and replaced with dirt from a place where poultry have not been maintained.