Bovine Tuberculosis

INTRODUCTION

A potentially serious infectious bacterial disease that mainly affect the lungs. The bacteria that cause tuberculosis are spread when infected person to another through tiny droplets coughs or sneezes.

Tuberculosis is a chronic disease of many animal species and poultry caused by bacteria of the genus Mycobacterium. It is characterized by development of tubercles in the organs of most species. Bovine tuberculosis is caused by Mycobacterium bovis. It is a significant zoonotic disease.

Mycobacteria invade the cattle by respiratory and oral route.

Lesions of Tuberculosis include:

• Acute military
• Nodular lesion
• Chronic organ tuberculosis

TRANSMISSION

• An infected animal is the main source of transmission.
• The organisms are excreted in the exhaled air and in all secretions and excretions.
• Inhalation is the chief mode of entry and for calves infected milk is an important source of infection
• When infection has occurred, tuberculosis may spread;
• By primary complex (lesion at point of entry and the local lymph node).
• By dissemination from primary complex.
• Congenital infection in the bovine fetus occurs from infected dam.
• Man is susceptible to the bovine type.
• Super infection is specific in cattle

CLINICAL SIGNS

In early stages (2-3months) of tuberculosis clinical signs are not visible.

In later stages, clinical signs may include:

• Emaciation
• Lethargy
• Weakness
• Anorexia
• Low grade fever
• Pneumonia with a chronic
• Moist cough
• Enlargement of lymph node

ANTEMORTEM FINDINGS

1. Low grade fever
2. Chronic intermittent hacking cough and associated pneumonia
3. Difficult breathing
4. Weakness and loss of appetite
5. Emaciation
6. Swelling superficial body lymph nodes

POSTMORTEM FINDINGS

1. Tuberculosis granuloma in the lymph nodes of the head, lungs, intestine and carcass. These usually are well defined capsule enclosing a caseous mass with a calcified center. They are usually yellow in color in cattle, white in buffaloes and greyish when in other animals.
2. Active lesions may have a reddened peripheral and caseous mass in the center of a lymph node.
3. Inactive lesions may be calcified and encapsulated.
4. Nodules on the pleura and peritoneum.
5. Lesion in the lungs, liver, spleen, kidney.
6. Bronchopneumonia.
7. Firmer and enlarged udder, particularly rear quarters.
8. Lesions in the meninges, bone marrow and joints.

CONTROL/PREVENTION

The only way to be protected from disease is through prevention. Prevention of Tuberculosis in a herd can be prevented by:

• Limiting the exposure of the herd to other infected cattle 
•  Eliminate any possible interaction infected wildlife (e.g., deer)
• Proper storage of feed to avoid contamination of feed by infected animals and/or aerosol droplets
• Vaccination, a vaccine was created for Mycobacterium bovis in the 1920’s by Calmette and Guerin.

The control of Tuberculosis can also be achieved by

• Testing and eradication of infected animals
• Culling of infected animals.

DIAGNOSIS

Tuberculosis clinical signs are not specifically distinctive and do not allow to establish a diagnosis with certainty.

The standard method for detecting tuberculosis is the tuberculin test, where a small amount of tuberculosis protein (antigen) is injected intradermal and the immune reaction is evaluated by measuring the skin thickness after 72hrs. Definitive diagnosis is made by growing the bacteria in the laboratory, a process that takes 8 weeks.

JUGDEMENT

• Carcass of an animal affected with tuberculosis requires additional postmortem examination of lymph nodes, joints, bones and meninges.
• It is suggested that the codex Alimentarius judgment recommendation for cattle and buffalo carcasses be followed.
• Carcasses are condemned.
• Where an eradication scheme has terminated or in cases of residual infection or re infection.
• In final stages of eradication- natural prevalence low
• During early stages in high prevalence areas.
• Carcass of a reactor animal without lesions may be approved for limited distribution. If the economic situation permits, this carcass should be condemned
• Heat treatment of meat is suggested during early and final stages of an eradication program.
• In some countries, the carcass is approved if inactive lesions (calcified and or encapsulated) are observed in organs and without generalization in lymph nodes of carcass.

EPIDEMEOLOGY

  An understanding of epidemiology of Mycobacterium tuberculosis is critical for effective control. Epidemiology of tuberculosis is best understood from both animal and human aspect

  Mycobacterium bovis is the main cause of tuberculosis in cattle, deer, and other animals.

MYCOBACTERIUM TUBERCULOSIS COMPLEX

Mycobacterium tuberculosis is a member of the Mycobacterium complex; the other members being Mycobacterium africanum and Mycobacterium bovis.

Mycobacterium africanum is most commonly found in West Africa; it causes up to a quarter of cases of tuberculosis in the Gambia. The symptoms of infection resemble those of Mycobacterium tuberculosis. The infectivity is similar to Mycobacterium tuberculosis, and it is an important opportunistic pathogen in the setting of advanced immunosuppression due to HIV or other causes. Management is identical to the management for disease due to Mycobacterium tuberculosis.

Mycobacterium bovis is the main cause of tuberculosis in cattle, deer, and other mammals. The human bacillus may have arisen from M. bovis in the setting of animal domestication. Human M. bovis infection generally occurs in the setting of consumption of infected cow’s milk products, Bacille Calmette-Guérin (BCG) vaccination for Tuberculosis prevention, or intravesicular BCG installation for bladder cancer treatment.

BURDEN OF TUBERCULOSIS

The epidemiology of tuberculosis varies substantially around the world. The highest rates (100/100,000 or higher) are observed in sub-Saharan Africa, India, China, and the islands of Southeast Asia and Micronesia. Estimates provided by USAID in 2007 for South Sudan were 228 cases per 100,000 populations. In South Sudan, an estimated 18,500 people develop TB, and 5,300 die of Tuberculosis annually.

Poverty, HIV and drug resistance are major contributors to the resurging global epidemic (4, 5). Approximately 95% of Tuberculosis cases occur in developing countries. Approximately 1 in 14 new Tuberculosis cases occur in individuals who are infected with HIV; 85 percent of these cases occur in Africa. An estimated half million cases of multidrug resistant (MDR)-Tuberculosis also occur annually in Africans; even higher rates of drug resistant disease occur in Eastern Europe.

RISK FACTORS

Some people develop Tuberculosis disease within weeks of becoming infected before their immune system can fight the Tuberculosis bacteria. Other people may get sick years later, when their immune system becomes weak for another reason.

Overall, about 5 to 10% of infected persons who do not receive treatment for latent Tuberculosis infection will develop Tuberculosis   disease at some time in their lives. For persons whose immune systems are weak, especially those with HIV infection, the risk of developing Tuberculosis disease is much higher than for those with normal immune systems.

Generally, Animal and person at high risk for developing Tuberculosis disease fall into two

1. Animals who have been recently infected with TB bacteria.

2. Animals with medical conditions that weaken the immune system.

3.  Animals who have been recently infected with tuberculosis bacteria

These include:

• Animals that have close contacts with another animal with infectious TB disease.
• Animals who have emigrated from areas of the world with high rates of TB.
• Children less than 5 years of age who have a positive TB test.
• Persons from groups with high rates of TB transmission, such as homeless persons, injection drug users, and persons with HIV infection.
• Persons who work or reside with people who are at high risk of TB in facilities or institutions such as hospitals, homeless shelters, correctional facilities, nursing homes and residential homes for those with HIV
• Animals with medical conditions that weaken the immune system
• Babies and young animals often have weak immune systems. Other people can have weak immune systems especially those with any of these conditions:
• HIV infection.
• Substance abuse
• Silicosis.
• Diabetes mellitus.
• Severe kidney disease.
• Low body weight.
• Organ transplants.
• Head and neck cancer.
• Medical treatments such as corticosteroids or organ transplant.
• Specialized treatment for rheumatoid arthritis or Cohn’s disease.

In South Sudan although the exact incidence of HIV/AIDS among Tuberculosis cases is not known, HIV prevalence appears to be on the rise. Data from limited population surveys show HIV prevalence rates range between 1 and 8 percent among the general population, with higher rates (up to 25 percent) found in border towns. Multidrug-resistance.

DIFFERENTIAL DIAGNOSES

• Lung and lymph node abscess
• Pleurisy pericarditis
• Chronic contagious pleuropneumonia
• Actinobacillosis
• Mycotic and parasitic lesion
• Johne’s disease
• Tumors
• Lymphomatosis

REFERENCES:

• Manual on meat inspection for developing countries. Specific diseases of cattle; Chapter three. D. Herenda in cooperation with P.G. Chambers A. Ettriqui P. Seneviratna T.J. da Silva
• WebMD Medical Reference, Reviewed by Sabrina Felson, MD

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