Ben Sun, DVM, MPVM, California Department of Public Health, says that in earlier times, tuberculosis (TB) transmission was common from cattle to humans through contaminated milk products, but drastic reductions occurred due to disease control and pasteurization. “The majority of transmission now is from countries where infection is more prevalent in cattle,” he said, speaking at the 2010 National Institute for Animal Agriculture annual meeting in Kansas City, Mo. However, he noted that there is a more regional presence of human tuberculosis with large Hispanic populations coupled with importation of contaminated dairy products or consumption of raw dairy products.

TB can transmit between cattle and humans in a variety of ways. There is cattle-to-cattle transmission, human-to-human transmission, cattle-to-humans (through contaminated dairy products) and human-to-cattle transmission (reverse zoonosis). Foodborne transmission through products such as raw milk is the biggest concern.

A 2007 case of bovine tuberculosis (TB) in California stemming from an animal purchased at the central California dairy of Steve Maddox, Riverdale, Calif., has caused Maddox to put in place strategic TB prevention practices. Maddox discussed the measures he’s using to not just keep cow-to-cow transmission from happening, but to also address the potential human transmission factors. 

On-farm TB prevention
Maddox lists the strategies he uses to keep TB off of his dairy farms:

  • Maintain a closed herd if possible.
  • Record individual animal identification and maintain accurate records.
  • Isolate and test purchased additions.
  • Test and isolate cattle re-entering the herd (i.e. contract-raised heifers).
  • Arrange diagnostic workups and necropsies for potential or suspected TB cattle.
  • Establish TB testing for employees.
  • Enhance biosecurity.

Sun added that human-to-cattle TB prevention includes:

  • Healthy workers.
  • Avoid having employees work with other herds.
  • Education/training of workers.
  • Do not contaminate feed.
  • Know the signs of TB.
  • Avoid high exposure and risk (such as consuming raw dairy products).
  • Farm and human sanitation/hygiene.

Employment TB Program
Maddox has implemented these employee TB prevention steps:

  • Pre-employment, employees must be negative to TB.
  • Employees are required to have ongoing testing every two years.
  • If traveling internationally, 3-6 months post-return, employees must be TB tested.
  • All positive skin-test employees are to receive a chest x-ray. A positive x-ray prohibits work until medical release.
  • Employees are required to complete a TB health questionnaire satisfactory to medical personnel (Maddox suggests working with an attorney on this document).

Recommendations to USDA
Maddox also makes these recommendations to the USDA for bovine TB prevention:

  • Institute mandatory RFID in the dairy industry.
  • Initiate strategic plans for control of infectious diseases on dairies.
  • Control Mexican feeder cattle.
  • Most importantly, immigration reform that allows workers to come into the U.S. on a legitimate program that includes testing for drugs and TB.