ASK THE VET (Tuberculosis)

Tuberculosis is an infectious granulomatous (walled off area of infection) disease of animals and people. It is caused by an acid-fast bacterial rod known as mycobacterium. In humans, TB is caused by M. tuberculosis, M. bovis, and occasionally, M. avium. In birds, M. avium is the usual agent although M. bovis and M. tuberculosis can cause disease as well. In humans, the incidence of TB is increasing, especially in people whose immune systems are compromised, such as those infected with the AIDS virus.

All birds are susceptible to avian tuberculosis. It is most prevalent where there is a high population density, such as in zoos, or collections of birds. Brotogerid parakeets, ringneck and related parakeets, amazons, Grey Cheeks, and pionus parrots seem to be especially susceptible.

Although sudden death can occur in a bird with normal body weight, the usual presentation of a bird with TB is one of progressive weight loss in spite of a good appetite. Depression, diarrhea, increased thirst, and respiratory difficulty may also be present. Decreased egg production often occurs in birds that were laying eggs. Once the disease appears, it is impossible to eliminate. Eventual death is the usual outcome.

Oral ingestion of food and water contaminated with feces is the most common method of infection. Once ingested, the organism spreads throughout the bird's body and is shed in large number in the feces. If the bacterium is inhaled, pulmonary lesions may develop. Skin invasion may occur as well. Although spread via infected eggs can occur, it is not a common means of dissemination.

Diagnosis of TB in a live bird is often very difficult. Weight loss, depression, and diarrhea occur with many different diseases. Serological testing and skin tests used to diagnose TB in people don't work well in birds. It is difficult to culture the organism in the lab. An elevated WBC (White blood cell) count may be present, as well as anemia (low red blood cell count). It is sometimes possible to find acid-fast bacteria in the feces. This however, is not specific because other acid-fast bacteria that are not TB may also be present. The bacteria must be cultured in order to identify it.

An X-ray may demonstrate an enlarged liver, spleen, and nodules in the lungs. Biopsy of the liver is one of the best ways to diagnose the disease.

At postmortem, noncaseated (liquid), non-mineralized nodules may be present in the digestive tract, liver, spleen and lungs. Special stains are used to identify the mycobacteria in these modules.

Treatment of infected birds is controversial. Some veterinarians feel that a combination of several different drugs can be used successfully. Treatment must be done for a minimum of 1 year. Other people feel that it is unwise to treat positive birds, since children and immunocompromised adults may be susceptible to the organism.

As one can appreciate, TB is very difficult to screen for in a live bird. New birds should be quarantined for several months to a year, before they are introduced into a collection. Physical examinations, fecals, CBC, several negative acid-fast stains and endoscopy should be done if possible.