Summary about Disease
Bovine tuberculosis (bTB) is a chronic, infectious disease of cattle caused by the bacterium Mycobacterium bovis (M. bovis). It primarily affects the lungs and lymph nodes but can spread to other organs. While commonly associated with cattle, it can infect other mammals, including humans. The disease poses a significant economic burden due to trade restrictions, testing costs, and animal losses.
Symptoms
Symptoms of bovine TB are often subtle and develop slowly. In early stages, infected animals may show no visible signs. As the disease progresses, symptoms can include:
Progressive weight loss
Lethargy
Weakness
Fluctuating fever
Chronic, moist cough
Enlarged lymph nodes (particularly in the head and neck)
Difficulty breathing (in advanced cases)
Causes
The primary cause of bovine TB is infection with the bacterium Mycobacterium bovis. Transmission occurs mainly through:
Inhalation: Aerosol droplets containing the bacteria, expelled through coughing or sneezing.
Ingestion: Contaminated feed or water.
Direct contact: Close contact with infected animals.
Congenital transmission: Rarely, from mother to calf in utero.
Indirect transmission: Via contaminated environments.
Medicine Used
There is no practical or approved treatment for bovine TB in cattle. Treatment is not pursued because it is not economically feasible and could lead to the development of antibiotic-resistant bacteria, potentially endangering public health. Control efforts focus on eradication through testing and removal of infected animals.
Is Communicable
Yes, bovine TB is communicable. It can spread between cattle, to other animals (including wildlife such as deer, badgers, and others), and to humans (zoonotic).
Precautions
Precautions to prevent the spread of bovine TB include:
Regular testing of cattle: Implement robust testing programs.
Quarantine of infected herds: Isolate infected animals to prevent further transmission.
Culling of infected animals: Removal of infected animals from the herd is crucial for eradication.
Biosecurity measures: Maintain strict biosecurity protocols to minimize the risk of infection, including controlling animal movement, cleaning and disinfecting equipment, and managing wildlife interactions.
Pasteurization of milk: Pasteurization effectively kills M. bovis in milk, preventing transmission to humans.
Personal protective equipment (PPE): Veterinarians and farmworkers handling potentially infected animals should wear appropriate PPE, such as masks and gloves.
Proper ventilation: Ensure adequate ventilation in barns and other livestock housing.
How long does an outbreak last?
The duration of a bTB outbreak can vary significantly depending on several factors, including:
Herd size: Larger herds may take longer to clear.
Prevalence of infection: Herds with a higher percentage of infected animals will require more time to eradicate the disease.
Effectiveness of control measures: The speed and efficacy of testing, culling, and biosecurity measures influence the duration.
Presence of wildlife reservoirs: If wildlife reservoirs of infection are present, eradication can be more challenging and prolonged.
Compliance with regulations: The degree to which farmers and ranchers adhere to TB control regulations and recommendations affects the outcome. Outbreaks can last from several months to several years, depending on the complexity of the situation.
How is it diagnosed?
Bovine TB is primarily diagnosed through:
Tuberculin skin test (TST): This involves injecting a small amount of tuberculin (a protein derived from M. bovis) into the skin of the animal. If the animal has been exposed to *M. bovis*, a localized swelling will develop at the injection site within 72 hours.
Interferon-gamma (IFN-γ) assay: This blood test measures the animal's immune response to M. bovis. It can detect infection earlier than the skin test in some cases.
Post-mortem examination: Examination of lymph nodes and lungs for lesions characteristic of TB during slaughter or necropsy.
Bacterial culture: Isolation and identification of M. bovis from tissue samples.
Polymerase chain reaction (PCR): Detection of M. bovis DNA in tissue samples.
Timeline of Symptoms
The timeline of symptoms can vary greatly between individual animals.
Early stages: Usually asymptomatic; may not show any visible signs for months or even years after infection. The immune system may control the infection, preventing the rapid development of symptoms.
Progression: Gradual weight loss, lethargy, and fluctuating fever may appear over weeks to months.
Advanced stages: Chronic cough, enlarged lymph nodes, and difficulty breathing may develop over several months. In severe cases, the animal may become emaciated and die.
Note: Some animals may never develop clinical signs, even though they are infected and capable of transmitting the disease.
Important Considerations
Zoonotic potential: Bovine TB can infect humans, usually through the consumption of unpasteurized milk or close contact with infected animals. Public health measures are essential to prevent human infections.
Economic impact: Bovine TB can have significant economic consequences for the agricultural industry, including trade restrictions, testing costs, and animal losses.
Wildlife reservoirs: The presence of wildlife reservoirs of infection, such as deer and badgers, can complicate eradication efforts.
Trade implications: Countries with high prevalence rates of bovine TB may face restrictions on the export of cattle and other livestock products.
Regional variations: The prevalence of bovine TB varies significantly across different regions and countries.
Importance of collaboration: Effective control and eradication of bovine TB require collaboration between government agencies, veterinarians, farmers, and wildlife managers.