Merck Manual

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Professional Version

Mycobacterial Infections in Animals


Nuno Santos

, PhD, CIBIO-InBIO, University of Porto

Reviewed/Revised Mar 2023 | Modified Jun 2023

Mycobacteria found in soil and water have been isolated from tissues of animals. Mycobacterium fortuitum, a rapidly growing organism highly resistant to penicillin G, streptomycin, ampicillin, sulfamethoxazole, and chloramphenicol, has been associated with mastitis in cows Mastitis in Cattle With few exceptions, mastitis occurs when microbes enter the teat via the teat canal. Almost any microbe can opportunistically invade the teat canal and cause mastitis. However, most infections... read more Mastitis in Cattle , pulmonary infections in dogs, lymph node lesions in pigs and certain exotic animals, and cutaneous lesions in cats and dogs. Drug susceptibility tests indicate that M fortuitum is inhibited by capreomycin and by ethionamide.

Mycobacterium chelonae, another rapidly growing mycobacterium, has been isolated from contaminated wounds and injection abscesses.

Fish and other cold-blooded animals may be infected with Mycobacterium marinum, M chelonae, Mycobacterium abscessus, certain serovars of Mycobacterium avium complex, or Mycobacterium intracellulare, which have been recognized as zoonotic, particularly in immunocompromised humans.

A photochromogenic organism, Mycobacterium kansasii, has been isolated from pigs, cattle, deer, cats, and nonhuman primates.

Mycobacterium avium paratuberculosis, the cause of Johne’s disease Paratuberculosis in Ruminants Paratuberculosis, caused by Mycobacterium avium paratuberculosis , is a chronic, contagious granulomatous enteritis characterized in cattle and other ruminants by progressive weight loss... read more Paratuberculosis in Ruminants , has been isolated from domestic and wild ruminants. It causes a slowly progressive diarrheal disease resulting in weight loss and emaciation. Lesions occur most often in the ileocecal valve and associated lymph nodes. Diagnosis should be confirmed by an organism-based test. No treatment is available.

Mycobacterium scrofulaceum, a scotochromogen, has been isolated from lymph node lesions in pigs, cattle, and certain nonhuman primates. Mycobacterium xenopi, a slow-growing scotochromogen, has been isolated from pigs, ferrets, seafowl, reptiles, amphibians, and fish. These organisms should be differentiated from Mycobacterium gordonae and Mycobacterium flavescens and from other slow-growing scotochromogenic mycobacteria that are common contaminants of water.

Numerous nonpathogenic, nonphotochromogenic mycobacteria that closely resemble potential pathogens can be isolated from water and soil. Mycobacterium nonchromogenicum, Mycobacterium gastri, Mycobacterium triviale, and Mycobacterium terrae, which closely resemble strains of the M avium complex, may be differentiated by in vitro laboratory examinations, including molecular techniques.

Although opportunistic mycobacteria usually do not produce progressive disease, except in immunocompromised animals, they may be important in inducing transient tuberculin skin sensitivity. The application of comparative skin tests, using biologically balanced purified protein derivatives (PPDs) prepared from culture filtrates of Mycobacterium bovis and M avium, provides useful information on the possible cause of tuberculin skin sensitivity. Tuberculins prepared for veterinary use, containing ~5,000 tuberculin units per test dose, should be used for skin tests in free-range, captive, wild, and exotic animals.

Mycobacterium lepraemurium, a nonphotochromogenic, slow-growing, acid-fast bacillus, causes a disease in cats and rats that is similar in some respects to leprosy in humans. It can be grown on media containing cytochrome C and alpha-ketoglutarate. Mycobacterium leprae, the cause of leprosy in humans, has been found in spontaneously occurring disease in armadillos, red squirrels, and nonhuman primates. This organism has not been grown on artificial culture medium; however, M leprae DNA can be identified by molecular techniques.

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