In this episode, AABP Executive Director Dr. Fred Gingrich discusses an old disease with some new research, bovine tuberculosis (TB). Our guest is Dr. Jason Lombard, an AABP member and veterinary epidemiologist with USDA’s field epidemiologic investigation services. The findings and conclusions in this podcast are Lombard’s and should not be construed as USDA or government opinion or policy. 

 At the beginning of the 1900s, TB was the leading cause of death in the U.S., and it was estimated that 10% of people with TB had bovine TB, likely due to consumption of unpasteurized milk. This began the U.S. state-federal bovine TB eradication program that many veterinarians are familiar with in working with cattle operations. In 1917, approximately 5% of the cattle population (3.2 million head) were estimated to be infected with TB and in 1949, less than 0.5% were infected. In 2021, 61 head of cattle were found to be infected with TB which is 0.00006%, representing a 99.9% decrease since the eradication program began in 1917. The primary method of surveillance in the U.S. is now slaughter surveillance. In 2019, it was estimated that 4% of the U.S. population (13 million people) have latent or clinical TB. Of those clinical with TB, 1.9% were determined to be M. bovis. This strain of TB results in extrapulmonary disease in humans which can have implications for methods of transmission from humans to cattle, such as via the urinary system.

Lombard reviews three cases in the U.S. where it was documented that humans had transmitted M. bovis to cattle (human to animal transmission). These cases occurred on dairy farms in North Dakota and Wisconsin and a third case on a Texas heifer ranch. Given these cases, Dr. Lombard discusses how veterinarians can become more involved in TB prevention on beef and dairy operations. Biosecurity remains the primary method of prevention since TB usually enters a herd through contact with infected livestock, wildlife or humans. In addition, veterinarians can discuss with producers evaluating the risk of TB to humans and cattle on their farms. Some farms have implemented TB testing protocols of employees to promote a healthy workforce and ensure animal health. Veterinarians can also stress the importance of animal disease traceability. Use of official animal ID and accurate record keeping can assist state and federal animal health officials to conduct thorough and efficient trace investigations.

Relevant publications:

Dean GS, Rhodes SG, Coad M, Whelan AO, Cockle PJ, Clifford DJ, Hewinson RG, Vordermeier HM. Minimum infective dose of Mycobacterium bovis in cattle. Infect Immun. 2005 Oct;73(10):6467-71. 

 Lombard JE, Patton EA, Gibbons-Burgener SN, Klos RF, Tans-Kersten JL, Carlson BW, Keller SJ, Pritschet DJ, Rollo S, Dutcher TV, Young CA, Hench WC, Thacker TC, Perea C, Lehmkuhl AD, Robbe-Austerman S. Human-to-Cattle Mycobacterium tuberculosis Complex Transmission in the United States. Front Vet Sci.  2021 Jul 12;8:691192. 

 McCluskey B, Lombard J, Strunk S, Nelson D, Robbe-Austerman S, Naugle A, Edmondson A. Mycobacterium bovis in California dairies: a case series of 2002-2013 outbreaks. Prev Vet Med. 2014 Aug 1;115(3-4):205-16. 

 Olmstead, A.L., and Rhode, P.W. (2004). An Impossible Undertaking: The Eradication of Bovine Tuberculosis in the United States. The Journal of Economic History 64, 734-772.