STEVENS POINT, Wis. – Following the discovery of a tuberculosis-infected cow in a Dane County, Wis., dairy herd last fall, concerns about protecting both livestock and people from the disease have raised levels of awareness and interest in livestock producers throughout the state.
    Dr. Suzanne Gibbons-Burgener, an infectious diseases epidemiologist from the Communicable Disease Epidemiology Section of the Wisconsin Department of Public Health, spoke to those in attendance at the Agricultural Safety Connection Educational Seminar about the need to understand the disease and how it can be spread and prevented in both animals and humans Jan. 8 in Stevens Point, Wis.
    “Tuberculosis is an ancient bacterial disease,” Gibbons-Burgener said. “It was named after the nodules, or tubercles, in lymph nodes of affected animals and humans. It is caused by a bacterium that is in the Mycobacterium tuberculosis complex (MTBC). The MTBC bacteria need to be in a mammalian host to really survive and replicate.”
    According to Gibbons-Burgener, the need for a mammalian host makes TB unique as there are other Mycobacteria that can live and survive in the environment in other classes of animals and even in plants.
    The MTBC is comprised of less than one dozen closely related Mycobacterium species, all of which are host-adaptive. Some of the types of species of Mycobacterium include M. tuberculosis which is adapted to and survives best in humans and primates; M. bovis is adapted to cattle; M. microti is adapted to voles; M. caprae is adapted to goats; and M. pinnipedii is adapted to seals.
    Gibbons-Burgener said the species all have the potential to infect and cause disease in animals besides their preferred hosts.
     “There are also hundreds of Mycobacterium species that do not fall in the MTBC,” Gibbons-Burgener said. “During 2015 the Wisconsin State Laboratory of Hygiene identified Mycobacterium in 1,371 bacterial isolates from ill human patients. Only 60, or 4.4 percent, of those isolates were in the MTBC. The remaining were non-MTBC.”
    The state of Wisconsin averages about 50 human cases of tuberculosis disease each year. Gibbons-Burgener said the vast majority of those cases are caused by M. tuberculosis. She said generally there is only one case every other year of M. bovis found in human patients. Globally, about one-third of the world’s population is infected with TB. Most of those people are not infectious, however, but carry a latent form of the bacteria. Acute, or infectious, TB in humans will typically cause a cough with difficulty breathing. It is accompanied by a fever, night sweats and weight loss.
    “The primary of transmission of M. bovis occurs between cattle via inhalation,” Gibbons-Burgener said. “It can be shed in milk, which serves as a major source of infection in calves and humans who consume unpasteurized dairy products.”
    Consumption of unpasteurized dairy products made from the milk of an infected cow is the primary way humans contract M. bovis. Gibbons-Burgener said humans with pulmonary TB caused by M. bovis can spread the bacterium more easily to other humans than they can to cattle.
    “At the turn of the 20th century, we recognized the essentials for producing a safe milk supply,” Gibbons-Burgener said. “You start with healthy cows and healthy people, and then provide sanitary production units. Pasteurization is one of the greatest public health inventions that we know and still use to this day. Many countries in the world have not yet achieved the same level of food safety that we have achieved here in the U.S.”   
    Gibbons-Burgener said aerosol transmission of M. bovis from cattle to humans is uncommon, but it may occur when close contact occurs to the head or mouth of a coughing cow with bovine TB. It can also be transmitted during the necropsy of an infected animal, or during invasive thoracic or abdominal surgery, such as a DA or a cesarean section.
    “A worker with contagious pulmonary TB disease can generate tiny, infectious droplet nuclei when they cough or sneeze,” Gibbons-Burgener said of human to animal transmission. “This can affect cattle during ideal conditions, which can include performing activities in close proximity to the head and mouth of a cow in a confined space with limited ventilation. That allows for the droplets to remain suspended in the air for a long period of time.”
    Some farm activities pose minimal risk for human infection by M. bovis. These include handling calves under 2 months of age, handling of manure and urine, milking, feeding, and general cleaning and maintenance.
    Wisconsin’s human and animal health agencies are responsible for investigating and responding to cases of TB found in agricultural settings. In the state’s multi-agency response plan, if the department of public health determines a person who is infected with TB has had contact with animals, the department of agriculture or the department of natural resources is contacted, depending if the contact was with domestic or wild animals.
    If an animal is found to have TB, the chain goes the opposite way, with the department of agriculture or the department of natural resources contacting the department of public health to work to determine if people in contact with the animals have been infected. Risk assessments are preformed to decide if there is a concern for zoonotic transfer of the disease and determine necessary testing protocols.
    In order to reduce the risk for MTBC infection, Gibbons-Burgener recommends farms develop employee TB prevention policies which teach workers about the disease, the use of personal protection equipment, symptoms and risk factors, and providing periodic testing.
    In developing a TB prevention policy, producers need to consider who on their farm will be involved in the prevention program. They then need to decide when it will be implemented, whether it be at hiring only or carried on at periodic intervals. They also need to take into consideration where the testing and training will occur, if it will be provided on-site or will take place at a health care provider’s office. Producers will need to determine how they will implement their policies, navigating issues such as confidentiality, cost and cultural and linguistic barriers.
    While Wisconsin remains a low-risk state for TB, according to Gibbons-Burgener it is an important public health concern that everyone involved in agriculture needs to be aware of.