Tuberculosis in poultry, which is predominantly due to Mycobacterium avium infection, can affect all birds, although susceptibility varies by species. Infection is chronic, leading to emaciation, decreased egg production, granulomas in multiple tissues, and death. Diagnosis is usually easiest when based on gross lesions and demonstration of the bacteria in tissue samples. Treatment is not recommended, because its duration and cost make it unlikely to be successful. Contaminated premises should not be used to raise poultry. Although M avium can infect humans, serovars found in birds and humans are typically different. Nonetheless, precautions should be taken to avoid human exposure to infected birds.
Tuberculosis in poultry is predominantly due to infection with Mycobacterium avium—in particular, M avium avium. Tuberculosis is a chronic disease that occasionally occurs in small poultry flocks, game birds (pheasants, quail, and partridges), and, rarely, in commercial poultry. With the advent of free-range commercial flocks, the incidence may increase. The disease also occurs in captive pet birds.
In poultry, tuberculosis usually affects the entire flock; however, the disease typically presents to the veterinarian as an individually affected live or dead bird. Birds that die from the disease are extremely emaciated; they have dramatic loss of muscle and no body fat. Live, affected birds within the flock, when picked up, feel much lighter than nonaffected birds.
All avian species can be infected with M avium. Chickens, pheasants, and partridges are highly susceptible to infection; turkeys are less susceptible. Waterfowl (duck and geese) appear to be relatively resistant. M avium is also a cause of disease in swine and other mammals. Tuberculosis in avian species occurs worldwide.
Etiology and Pathogenesis of Tuberculosis in Poultry
Tuberculosis in birds is predominantly due to infection with M avium avium serovars 1, 2, and 3. However, some studies have reported cases of wild-caught psittacines being infected with Mycobacterium tuberculosis, presumably by their captors. More recent studies have described Mycobacterium genavense infection in pet birds and zoo-held avian collections. Avian infections with Mycobacterium bovis and Mycobacterium fortuitumhave also been reported.
Courtesy of Dr. Richard M. Fulton.
The most common route of M avium infection in poultry is oral. Once inside a bird, M avium bacteria replicate within macrophages (see intestinal lamina propria image), resulting in submucosal and serosal granulomas of the intestines. The granulomas ulcerate, releasing the bacteria into the intestinal lumen; the bacteria are then shed in the feces. Fecal shed leads to contamination of the environment. M avium may enter the bloodstream and be transported to the liver, spleen, and bone, resulting in granulomas in those organs.
Epidemiology and Transmission of Tuberculosis in Poultry
M avium infection is transmitted through contact with contaminated environments. The larger the infected population and the longer the birds remain on those premises, the higher the amount of bacterial contamination in the environment. M avium is typically ingested, although infection may be transmitted via aerosol.
M avium may persist in soil for many years; therefore, contaminated premises should not be used to raise poultry, swine, or other susceptible species.
Clinical Findings of Tuberculosis in Poultry
Decreased egg production or diminished weight gain may develop in poultry flocks affected by tuberculosis. In small flocks, these clinical signs are often missed until a few birds die. An observer walking through a flock might notice that the emaciated birds lag behind healthy birds. When affected birds are picked up, they feel lighter than unaffected birds.
The carcasses of birds that have died from tuberculosis reveal extreme emaciation; they have no fat reserves and show dramatic loss of muscle and prominent bone protuberances.
Courtesy of Purdue University Veterinary Medicine.
Lesions in tuberculosis consist of white, firm masses (granulomas) of various sizes in the intestine, liver, spleen, and bone marrow (see bone marrow granuloma image). The intestinal wall is thickened and pale, and serosal masses may be present.
Diagnosis of Tuberculosis in Poultry
Demonstration of acid-fast bacilli in postmortem samples by histological evaluation, culture, or PCR assay
Antemortem tests, such as intradermal injections and serological tests, are not reliable for the diagnosis of tuberculosis in poultry, because they can provide false-positive results. Fecal PCR assay can be done; however, shedding of M avium in the feces may be intermittent.
In poultry, tuberculosis is best diagnosed after necropsy. Acid-fast stains of crushed granulomas, upon histological examination of affected tissues, should reveal the presence of acid-fast bacilli (see acid-fast bacilli image). Unlike some mammalian tubercle infections, avian tuberculosis is characterized by numerous acid-fast bacilli. Culture using specific media may confirm the diagnosis, but it takes much longer for M avium than it does for other bacteria. PCR assay and genomic epidemiological sequencing may be warranted in cases of human exposure.
Courtesy of Dr. Richard M. Fulton.
With regard to the gross necropsy findings, causes other than tuberculosis that result in white masses in the liver and spleen include infection with salmonellae, staphylococci, and Escherichia coli (Hjärre disease), as well as Marek's disease, lymphoid leukosis, and reticuloendotheliosis viruses. However, only M avium is known to produce bone marrow granulomas.
Treatment, Control, and Prevention of Tuberculosis in Poultry
Treatment not recommended
Depopulation when possible
Environmental sanitation and biosecurity
Treatment of tuberculosis in poultry is not recommended, because antimicrobials are usually not efficacious. Thorough cleaning helps to lower bacterial load in the environment; however, it is unlikely to eliminate disease.
Tubercle bacilli accumulate in the environment over time. Thorough cleaning and disinfection after infected poultry flocks in an all-in all-out management system is feasible when birds of the same age are produced and the premises are depopulated. However, cleaning and disinfection might not be effective in housing systems that do not adopt all-in all-out management, as is the case with aviaries or rare bird collections, and tuberculosis infections in these systems can be devastating.
M avium is ubiquitous in the environment, and many wild birds are infected. Strict biosecurity is recommended to avoid introducing the pathogen to the premises.
Zoonotic Risk of Tuberculosis From Poultry
Although M avium can infect humans, the serovars of M avium in infected humans are different from those in infected avian species. The serovars in humans are more closely related to those in swine than to those in birds. Nevertheless, special precautions should be taken when dealing with Mycobacterium-infected birds.
Key Points
Tuberculosis can affect all birds, but susceptibility varies by species.
Diagnosis is based on postmortem identification of Mycobacterium avium by histological evaluation, culture, or PCR assay.
Treatment is not recommended, because of its duration and cost and because antimicrobials are usually not efficacious.
For More Information
Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley Blackwell; 2020.
Boulianne M, ed. Avian Disease Manual. 8th ed. American Association of Avian Pathologists; 2019.
