Avian tuberculosis is chronic bacterial infection that spreads slowly through a flock. All bird species appear to be susceptible, however pheasants seem highly susceptible whereas turkeys rarely succumb to the disease. The disease is more common in captive than wild birds, however it is uncommon in poultry flocks due to the poultry husbandry practices and their short life span. Tuberculosis has been found in emus and other ratites and has also shown to cross-infect 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 and affected hens are usually more than one year old. The disease in birds is characterised by gradual weight loss, sluggishness and sometimes lameness. Combs and wattles shrink and become pale. 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.
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.
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.