Zoonotic Diseases (Birds -Humans): Avian Tuberculosis

Zoonotic diseases are diseases that are transmissable from animals to humans. Young children, elderly adults and individuals with poorly functioning immune systems are at the greatest risk of being infected by a zoonotic disease.

While there are a number of diseases which can be transmitted by companion birds, many are more likely to be transmitted by poultry or wild birds. If your bird has been examined by an avian veterinarian and is considered healthy, the risks of infection are significantly reduced.

The following diseases in birds which are of reasonable significance include: Chlamydiosis (Psittacosis) , Salmonellosis, Campylobacteriosis, New Castles Disease, Allergic Alveolitus, Mycobacteriosis (Avian Tuberculosis), Influenza, Giardia, and Cryptosporidiosis.

Chlamydiosis (Psittacosis or Parrot Fever) and Salmonellosis were discussed in Zoonotic Diseases – Part I. Allergic Alveolitus, Campylobacteriosis and New Castles Disease were discussed in last month’s article, Zoonotic Diseases – Part II. Part III addresses Avian Tuberculosis.

Avian Tuberculosis (Mycobacteriosis)

Avian Tuberculosis occurs throughout the world and has been found in the waterfowl, turkeys, psittacines, passerines, columbiformes and raptors.

In psittacines, tuberculosis is usually caused by Mycobacterium aviumMycobacterium intracellulare and Mycobacterium genovenseM. tuberculosis and M. bovis have occassionally been isolated in birds. Humans are more commonly infected with M. tuberculosis and occasionally M. bovis. It is believed that immunocompetent humans are resisitant to the strains of tuberculosis found in birds, but that immunocompromised people – such as those infected with HIV, those on chemotherapy, the elderly and children are at increased risk.

Avian tuberculosis is transmitted by ingestion and inhalation of aerosolized infectious organisms from feces. Incubation in birds is weeks to months. Although many species of birds can be infected, the majority of cases occur in older amazons and grey cheeks. M.avium, the most common cause of tuberculosis in birds is often found in soil and water. It can survive for a long period of time in the environment and can multiply in inanimate objects.

Three types of syndromes may occur in birds. The classic form is that of tubercles or granulomas in many organs. A second form is the paratuberculosis form with lesions in the intestional tract. This is often seen in amazons, pionus, and Brotogeris parrots. With this form, high numbers of organisms are shed in the feces. A third form is a nontuberculous form or atypical form that is very difficult to recognize. This form commonly occurs in finches, canaries, and small pisttacines. The liver is usually very enlarged and large numbers of mycobacteria are found in cytology and histopathology.

Birds with the intestional form often present with chronic wasting disease – and Proventricular Dilitation Syndrome is often one of the suspected possible diseases. In addition to weight loss, depression, diarrhea, increased urination (polyuria), abdominal distention, lameness and difficulty in breathing may be present.

In adult humans, tuberculosis frequently affects the lungs, producing respiratory signs. In young children, the cervical lymph nodes are often involved, while immunocompromised people often have the disseminated form.

Diagnosis of tuberculosis in the live bird can be very difficult due to intermittent fecal shedding and obscure signs. Physical findings, very elevated white blood cell and low red blood cell count and other diagnostic tests which include radiology (x-rays), endoscopy and identification of acid fast bacteria in feces or tissues can lead to a preliminary diagnosis. Definitive diagnosis is based on culturing the organism from the feces or from an organ. Not all acid fast organisms are mycobacteria, therefore just identifying acid fast organisms does not provide a conclusive diagnosis. New tests that may aid in the diagnosis include the DNA probe and the polymerase chain test.

Erradication is difficult due to the chronic carrier state and intermittent shedding of a large number of organisms.

If a positive bird is identified, it should be separated from the collection. Treatment of a positive bird is contaversial because of the large number of organisms shed in the feces and because the organism is resistant to many of the drugs used to treat human T.B. The infected bird must be treated for a long period using combination drug treatment.

All contact birds should be quarantined for 2 years and tested at 6-12 week intervals.

People who are infected with human tuberculosis should not own birds, since these people may serve as a source of infection for their pet birds.

Information on the remaining transmissable diseases mentioned at the beginning of the article – Influenza, Giardia, and Cryptosporidiosis – will appear in Zoonotic Diseases – Part IV in next month’s issue.