Tuberculosis Disease in Cattle

Bovine tuberculosis (TB) is a contagious disease caused by the bacteria Mycobacterium bovis. Because of its large host range, bovine TB can infect all warm-blooded animals. All species are not equally susceptible; some are spill-over (end) hosts and others who are carriers or maintenance hosts. Wild ruminants and carnivores are also affected and are the natural reservoirs of the infectious agent. Bovine TB is easily transmitted and spread among badgers, cattle, swine, buffalo and wild deer.

  1. Transmission and Spread

    • The spread of the infection from affected to other exposed animals in both industrialized and developing countries occurs when wild and domesticated animals share pastures, grazing and living territory. Documented examples of such spread include infection in badgers (Meles meles) in the United Kingdom and possums (Trichosurus vulpecula) in New Zealand.

      The second highest incidence of bovine TB is generally observed in places of intensive dairy production, notably in the milksheds of large cities. This problem becomes twofold where there is inadequate veterinary supervision.

    Other Affecting Factors

    • Various factors affect the efficiency in which M. bovis is spread within a cattle herd. Animals housed in confinement facilities will be at greater risk because of close contact. Cattle infected with bovine TB may shed bacteria in their breath, saliva, feces, urine and milk. The more animals within a herd shedding the bacteria, the greater the chance of spread to other animals. Cattle are more prone when they are poorly nourished or under stress. Growing heifers and younger cows are most at risk (Griffin et al., 1996). Living with livestock, other domestic animals can get infected, like hogs, dogs and also humans.

      M. bovis is killed by sunlight, but is resistant to desiccation and can survive in a wide range of chemical acids and alkalis. It remains alive for long periods in moist and warm soil. It can remain alive in cattle feces for a maximum of 8 weeks.

    Symptoms and Development

    • Bovine TB a chronic, progressive disease that can cause gradual deterioration of health; cattle lose appetite and become weak and lazy. The infection often starts with the lungs; coughing, nasal discharges and difficult breathing can occur, which will worsen as the condition gets severe. It may also occur in the intestines and other parts of the body. In some instances, superficial lymph nodes in the neck will develop large abscesses that may rupture and ooze fluids through the skin.

    Testing

    • The most common method of testing for bovine TB is the tuberculin skin test. In this test, tuberculin is injected into the animal. If the animal reacts with swelling, then the test is considered positive for the bacteria.

    Prevention and Control in Livestock.

    • Periodic health checks and testing of livestock on farms, along with monitoring of animals sent to slaughter or transported across, are intended to minimize bovine TB transmission from animals to humans. Vector eradication is important to protect the cattle. However, eradication of vectors (e.g., eradication of Australian brush-tailed possums, badgers in the UK and Ireland and wild deer in Michigan) puts at risk many social, ecological and economic values.

      Other prevention measures include removal of TB-infected animals from herds, meat inspection and milk pasteurization processes, improved sanitation and hygiene, proper food-handling methods, education of laborers regarding cleanliness and timely vaccinations for livestock and domestic animals living together.