Bovine tuberculosis
Bovine tuberculosis (TB) is a chronic contagious bacterial disease of livestock, and occasionally other species of mammals, resulting from infection with Mycobacterium bovis (M. bovis).
Signs of disease
The bacteria associated with the disease may lie dormant in an infected animal for years without causing clinical signs or progressive disease symptoms. It can reactivate during periods of stress or in older animals. When disease becomes progressive, it generally results in enlarged lesions which may be found in a variety of tissues including lymph nodes of the head and thorax, lung, spleen, and liver. In countries with eradication programs such as Canada, advanced disease is rare as most cases are detected at an early stage when infection typically consists of few or small lesions in the lungs or lymph nodes associated with the respiratory system.
Similarly, few infections in Canada progress to the point of presenting clinical signs. Nevertheless, when progressive disease does occur, the general signs are weakness, loss of appetite, weight-loss and fluctuating fever. When the lungs are extensively diseased, there can be an intermittent, hacking cough.
Disease spread
Infected animals with progressive disease shed the bacteria in respiratory secretions and aerosols, feces, milk, and sometimes in urine, vaginal secretions, or semen. As a result, disease may be spread in a variety of ways, most commonly through the inhalation of micro-droplets in aerosols from already infected animals and from the ingestion of contaminated food and water.
Certain scenarios can create considerable risk of transmission and introduction of bovine TB into other herds. The movement of infected animals from 1 herd to another with subsequent extended close contact can increase this risk. In addition, where infected wildlife are a reservoir of disease, there is the potential for ongoing transmission to livestock. Refer to bovine TB and wild animals for details.
Spread and transmission to humans
Bovine TB is a zoonosis, that is, an infection that can be transmitted from affected animals to people, causing a condition similar to human TB. People are most infected through the ingestion of unpasteurized dairy products derived from infected animals but also through inhalation of infectious aerosols or direct contact through breaks in the skin. Currently the risk to the general population in Canada is very low due to pasteurization of milk and livestock surveillance and testing programs.
Pasteurized milk and milk products are safe to consume.
Owners and handlers of infected cattle may be at risk and anyone who may have been exposed to an infected animal should seek medical advice. For those who contract Bovine TB it can be treated successfully with antimicrobial drugs. Untreated infections have the potential to be fatal. The CFIA imposes a quarantine on infected premises to help protect members of the public.
Controlling bovine tuberculosis in Canada
Bovine TB is a reportable disease in Canada. Any suspect cases must be reported to the CFIA. We investigate to determine if the disease is present. If bovine TB is confirmed on a premises, we alert the provincial health department and implements strict disease eradication measures to eliminate the infection and prevent further spread to livestock, humans, and wildlife. These measures include:
- implementing a quarantine and restricting the movement of animals and equipment
- humane destruction of all infected and susceptible exposed animals
- cleaning and disinfection of infected premises and equipment
- investigation and testing of all at-risk livestock herds which are epidemiologically associated with the infected premises (tracing)
- testing livestock and wildlife within a surveillance zone surrounding the infected premises; and
- testing any livestock herds that are re-stocked onto a premises where bovine TB was previously confirmed
Ongoing surveillance identifies any new infections maintaining Canada's current health status for TB and helps maintain current and attract new market access opportunities for Canadian livestock and livestock products. Because 95% of all commercial animals slaughtered in Canada are sent to a federal abattoir, our abattoir surveillance system looks primarily for tuberculosis-like lesions in the lymph nodes and lungs of slaughtered animals. In specific situations, abattoir surveillance is supplemented with live-animal testing which measures an animal's natural defense response against challenge to a derivative of the TB bacterium (tuberculin) injected into the skin. Although it is generally difficult to diagnose TB in live animals and tuberculin testing has limitations, this approach is recommended by the World Organisation for Animal Health (WOAH; founded as Office International des Épizooties (OIE)).
Compensation for owners of cattle ordered destroyed by the federal government
Owners can be compensated up to the maximum amount established under the Health of Animals Act. Additional information on compensation for animals ordered destroyed is available on our website.
Measures taken for cleaning and disinfecting a farm
The owner is responsible for the cleaning and disinfection of infected premises. Cleaning and disinfection can be carried out only after all the animals ordered destroyed have left the premises. Once a CFIA inspector has confirmed that the premises have been cleaned and disinfected, the quarantine can be lifted. The owner must wait 45 days before the premises can be restocked. Replacement animals will be subject to 2 annual negative herd tests. If the owner waits 2 years before restocking, no testing will be required.
Actions owners can take to prevent bovine tuberculosis
There is no preventative treatment to protect animals from becoming infected with tuberculosis. Cattle buyers can require that animals be tested before purchasing to mitigate the risk of infection. However, this does not provide 100% guarantee. Some infected livestock seem to be in prime condition, showing no evidence of infection until they are slaughtered. In some instances, the disease organisms lie dormant within the host's body for its lifetime, both in animals and in humans, without causing progressive disease. Owners who live in a geographic area known to have TB-infected wildlife (see the facts concerning bovine TB and wildlife) can implement biosecurity measures to mitigate the risk of disease transmission to their livestock.