What is Tuberculosis?

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Minnesota Board of Animal Health Reportable Disease of the Month Header

May 2017


Microscopic illustration of tuberculosis bacteria

What is it? Bovine tuberculosis is a bacterial disease caused by Mycobacterium and affects nearly all mammals, primarily hoof stock like cattle, bison, deer, elk and goats. Minnesota eradicated bovine TB twice, once in 1971 and again in 2005, and has held a disease-free status since 2011. The U.S. has a strong surveillance and response program for bovine TB and only identifies a handful of cases annually.

How is it transmitted? Transmission is tied to close contact with an infected animal. The disease can be spread via inhalation of infected particles when an animal coughs or sneezes. It can also be ingested through a shared food/water source or direct contact through an open wound. Evidence shows raw, unpasteurized, milk can transmit TB from an infected animal to either its calf or a person drinking the raw milk. The bacteria can survive in cool or moist conditions in the environment, outside of an infected animal.

What are the clinical signs? Signs can take months or years to appear. The infected animal will start to show weakness, loss of appetite, a fluctuating fever, increased coughing, and enlarged lymph nodes. Cattle, deer and elk typically have a mass of tissue (granuloma) called tubercles in their head and throat lymph nodes.

How is it diagnosed? Because the clinical signs of bovine TB are general, diagnosis is usually discovered at slaughter. Testing can be done on live animals with the caudal fold tuberculin test, which involves injecting tuberculin (purified bovine TB proteins) and looking for a skin reaction or swelling at the injection site. Infection can be confirmed during examination of a dead animal by testing any abnormal growths found in the animal’s lymph nodes or organs. There is no viable treatment for infected hoof stock animals and no vaccine.

Is there a risk to people? Yes, it is a zoonotic disease, which means people are at risk of contracting TB from an infected animal. This risk is reduced in the U.S. by food safety procedures like pasteurizing milk. There is a higher risk for those working directly with cattle and those people should be vigilant for any signs of illness in their herd.

How can it be prevented? Bovine TB can be controlled by testing at slaughter and a strong traceability program. This means the ability to successfully track where an individual animal has been throughout its life so exposure to other animals and people can be determined. Those “at risk” animals can then be segregated from their current herd and tested for bovine TB. This is known as testing and removal, which helps eliminate the bacteria from a population and ensure a safe and secure food supply chain. Routine cleaning and disinfection also reduces the chances of disease transmission.