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Epidemiologic Notes and Reports Bovine Tuberculosis -- Pennsylvania

In July 1989, the first outbreak of bovine tuberculosis reported in Pennsylvania since 1978 was detected during routine veterinary surveillance. No human cases were detected.

In a herd of 122 dairy cattle, 109 (89%) had positive skin tests for Mycobacterium bovis after routine cervical injection of bovine purified protein derivative (PPD). Since 1985, 11,336 cattle were known to have had contact (e.g., were in the same shows, corrals, or adjacent pastures or were transported together) with the index herd. All identified contacts were tested, and 12 (0.1%) had positive skin tests for M. bovis. All cattle with positive skin tests were euthanized and autopsied. Caseating granulomata were present in 16 (15%) of the 109 cattle with positive tests in the index herd but none of the 12 others with positive tests associated with the outbreak. Culture specimens of granulomatous mediastinal lymph nodes from 15 of the 16 grossly positive animals were positive for M. bovis.

Forty-two persons were identified who had consumed raw milk products from the index herd or had had direct contact through work with skin-test-positive cattle from the index herd during the past 5 years. Each of these persons was tested with an intradermal injection of 0.1 mL (5 tuberculin units (TU)) of tuberculin, PPD (Tubersol*, Connaught Laboratories, Inc.); none were positive (i.e., induration greater than or equal to 10 mm).

In Pennsylvania, more than 150,000 cattle annually are given caudal skin tests for M. bovis. Initially, 2500 TU of bovine PPD are injected intradermally into the caudal region of each animal. Any animal with palpable induration at the injection site 72 hours later receives confirmatory testing. Confirmatory testing consists of intradermal injection of matched equipotent doses of bovine and avian PPD (approximately 2500 TU and 800 TU, respectively) at separate sites in the cervical region. Induration at each site is measured 72 hours after injection and the results plotted against a standard curve (1). Animals with greater than expected induration at the bovine PPD site are considered positive and are euthanized and autopsied. If any cattle in a herd are positive for bovine PPD on confirmatory testing, the entire herd is retested with a cervical intradermal injection of 5000 TU of bovine PPD. All animals in the herd with induration in response to this double-strength bovine PPD injection are considered positive and are euthanized and autopsied.

Since 1978, less than five cattle per year have been euthanized and autopsied as a result of this protocol. In 1988, 178,013 cattle were given caudal skin tests in Pennsylvania, of which 378 (0.2%) were positive; two of these animals were positive on confirmatory cervical testing, and neither of these was positive on autopsy. The infected index herd reported here had been tested during 1988, and none had induration after caudal skin testing during that year. The veterinarian and source of tuberculin used in screening were the same in 1988 as in 1989, and no cattle were introduced into the herd between skin testing in 1988 and 1989.

The Pennsylvania Department of Health has advised all persons known to have contact with skin-test-positive cattle, especially consumers of raw milk products, to have skin testing performed by the department of health. The source of this outbreak is unknown. Reported by: R Yoxheimer, VMD, Pennsylvania Dept of Agriculture; D Tavris, MD, State Epidemiologist, Pennsylvania State Dept of Health. Bacterial Zoonoses Activity, Div of Bacterial Diseases, Center for Infectious Diseases; Div of Tuberculosis Control, Center for Prevention Svcs; Div of Field Svcs, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: From 1900 to 1930, M. bovis was isolated from 6%-30% of human tuberculosis patients in the United States and the United Kingdom (2,3). M. bovis can be transmitted from cattle to humans by consumption of raw milk or by respiratory exposure either to live infected cattle or to their carcasses (2-4). Humans with pulmonary M. bovis infections can transmit the disease to other humans or to cattle; cattle can also be infected by humans with M. bovis urinary tract infections (3). Cattle can transmit M. bovis to other cattle, probably by respiratory secretions (5,6). Since opportunistic Mycobacterium sp. also infect cattle, comparative testing with M. avium antigen is useful to enhance the specificity of skin testing with bovine PPD (7).

Declining rates of M. bovis isolation from human tuberculosis patients have been associated with milk pasteurization and with cattle inspection programs (2,3,8,9) such as that initiated in the United States in 1917. Since 1950, M. bovis has accounted for less than 1% of human tuberculosis cases in North America (2,9). M. bovis continues to cause disease in humans, however, and is sometimes fatal (10). Continued surveillance of cattle and continued warning against the consumption of raw milk are necessary to protect the human population from this infectious agent and can help eliminate tuberculosis by the year 2010 (11).

References

  1. US Department of Agriculture. Comparative cervical tuberculin

test results. Hyattsville, Maryland: US Department of Agriculture, 1977. (Veterinary services form no. 6-22D).

2. Karlson AG, Carr DT. Tuberculosis caused by Mycobacterium bovis. Ann Intern Med 1970;73:979-83.

3. Grange JM, Collins CH. Bovine tubercle bacilli and disease in animals and man. Epidemiol Infect 1987;92:221-34.

4. Robinson P, Morris D, Antic R. Mycobacterium bovis as an occupational hazard in abattoir workers. Aust N Z J Med 1988;18:701-3.

5. Roswurm JD, Ranney AF. Sharpening the attack on bovine tuberculosis. Am J Public Health 1973;63:884-6.

6. Neill SD, O'Brien JJ, McCracken RM. Mycobacterium bovis in the anterior respiratory tracts in the heads of tuberculin-reacting cattle. Vet Rec 1988;122:184-6.

7. Francis J, Choi CL, Frost AJ. The diagnosis of tuberculosis in cattle with special reference to bovine PPD tuberculin. Aust Vet J 1973;49:246-51.

8. Sjoegren I, Sutherland I. Studies of tuberculosis in man in relation to infection in cattle. Tubercle 1974;56:113-27.

9. Wigle WD, Ashley MJ, Killough EM, Cosens M. Bovine tuberculosis in humans in Ontario. Am Rev Respir Dis 1972;106:528-34. 10. Habib NI, Warring FC. A fatal case of infection due to Mycobacterium bovis. Am Rev Respir Dis 1966;93:804-10. 11. Advisory Committee for the Elimination of Tuberculosis. A strategic plan for the elimination of tuberculosis in the United States. MMWR 1989;38(no. S-3). *Use of trade names is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.

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