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Tuberculosis

Tuberculosis of animals and humans is caused by acid-fast bacilli of the genus Mycobacterium. Cattle, birds, and humans serve as the main reservoirs for these mycobacteria (PDF). Many laboratory animal species, to include nonhuman primates, swine, sheep, goats, rabbits, cats, dogs, and ferrets, are susceptible to infection, and contribute to the spread of the disease.

Nonhuman primates are of primary importance in the consideration of these diseases in the laboratory-animal environment. Most of the tuberculosis seen in nonhuman primates is caused by Mycobacterium tuberculosis, The human infectious dose of Mycobacterium tuberculosis is less than 10 bacilli. It has been postulated that a single bacterium is sufficient to infect a rhesus monkey.

Contact with nonhuman primates infected with Mycobacterium spp. is a recognized risk factor in the development of a positive tuberculin skin reaction. Nonhuman primates generally develop tuberculosis from humans during capture and exportation from parts of the world where the prevalence of the disease in humans and animals is high. However, the resurgence of human tuberculosis in the United States and the recognition of nosocomial outbreaks of multiple-drug-resistant tuberculosis (PDF) should serve as reminders that nonhuman primates can continue to be at risk for contracting tuberculosis from humans after introduction into established research colonies. The close confinement of these animals in holding facilities and in shipment crates creates an environment conductive to the spread of infection. The incidence of infection in a population varies with the species and the source of nonhuman primates. Although macaques are considered to be particularly sensitive to infection with M. tuberculosis, surveillance programs for tuberculosis should be extended to all species of nonhuman primates.

M. tuberculosis is transmitted via aerosols from infected animals or tissues. This mode of transmission also applies to most of the other mycobacterial species that might be encountered in laboratory animal contact. Humans can contract the disease in the laboratory through exposure of infectious aerosols generated by the handling of dirty bedding, the use of high-pressure water sanitizers, or the coughing of animals with respiratory involvement. Other potential sources of exposure include fecal shedding by animals with enteric infection and skin exudates resulting from scrofuloderma or suppurative fistulated lymph nodes. Mycobacterial disease can also be spread by entry of the bacilli into the body by ingestion or wound contamination.

The most common form of tuberculosis reflects the involvement of the pulmonary system, and is characterized by soft cough, which progresses to the coughing of blood or blood stained sputum. Other forms of the disease can involve any tissue or organ system, due to the spread via the blood stream. General symptoms as the disease progresses include weight loss, fatigue, lassitude, fever, chills, and cachexia.

The diagnosis of tuberculosis in humans and animals relies primarily on the use of the intradermal tuberculin skin test, chest radiography, and the demonstration of acid-fast bacilli in sputum smears. Definitive diagnosis can be obtained by isolating organisms in body fluids or biopsy specimens and identifying them with biochemical techniques of DNA probes. Additional information can be found in guidelines (PDF) established for the diagnosis and control of tuberculosis in humans.

The prevention and control of tuberculosis in a biomedical research facility require personnel education, periodic surveillance for infection in nonhuman primates and their handlers, isolation and quarantine of any suspect animals, and prompt euthanasia, necropsy, and microbiological and histopathological analysis of animals confirmed as positive. For extremely valuable animals, chemoprophylaxis, with effective antituberculosis agents may be elected.

The CDC recommends Animal Biosafety Level 3 (PDF) for animal studies using nonhuman primates experimentally or naturally infected with M. tuberculosis or M. bovis.