Tuberculosis: A Curse for Human and Animals

Pashu Sandesh, 07 July 2022

Prashant Prajapati, Vishal Prajapati, Daljeet Chhabra, Rakesh Sharda, Joycee Jogi, Ravi Sikrodia and Rakhi Gangil

Department of Veterinary Microbiology

College of Veterinary Science and AH MHOW

Tuberculosis (TB) is an infectious, granulomatous disease caused by various species of the genus Mycobacterium. It is characterized by the development of tubercles resulting in caseation and calcification. Tubercles may be seen in almost all the tissues and organs of the body except skeletal muscles.

Bovine tuberculosis is a zoonotic disease caused by Mycobacterium Bovis and it occurs worldwide. This disease is highly prevalent in tropical and sub-tropical countries. The OIE classified bovine tuberculosis as a List B disease, “a disease which is considered to be socio-economic or public health importance within countries and of significance to the international trade of animals and animal products” (Cousins, 2001).

I.C.A.R. granted schemes for Central and State Government livestock farms to screen out tuberculosis from 1980 onwards.

 According to FAO, the incidence of bovine tuberculosis is moderate in India.

Mode of transmission: 

• Direct contact with infected animals.
• Ingestion of contaminated food and water.
• Inhalation of infected droplets.
• Overcrowded premises, a common feeding trough.
• Human beings can acquire infection by consuming improper cooked milk and meat.

Susceptibility:

• Susceptibility of animals increases with increasing the age of animals.
• Females are more prone to infection than males.
• The deficiency of certain vitamins (Vit. A & C) causes the animals to acquire the infection more frequently. 

Pathogenesis:

• Bacilli get entered the body by inhalation of infected droplets.
• Inhaled bacilli are then phagocytosed by alveolar macrophages.
• These macrophages proliferate in numbers.
• The dead and degenerated macrophages are surrounded by epithelioid cells, granulocytes, lymphocytes and later multinucleated giant cells.
• The purulent to caseous, necrotic centre may calcify and the lesion may be surrounded by granulation tissue and a fibrous capsule to form the classic “tubercle.”
• The cellular composition and presence of acid-fast bacilli in tuberculous lesions differ between and within-host species.

Clinical findings:                         

• In advanced pulmonary tuberculosis, animals may develop a cough and intermittent fever.
• Bronchopneumonia is characterized by chronic, intermittent moist cough with later signs of dyspnea and tachypnea.
• Tuberculous mastitis facilitates the spread of infection to calves. 
• In the early stages of the disease, lesions may be difficult to detect at post-mortem examination.  

Diagnosis:

• Diagnosis on the basis of the clinical signs is very difficult. Radiography is useful in non human primates and small animals.
• Microscopic examination of sputum and other discharged material stained with Ziehl-Neelsen. 
• Confirmation of diagnosis is by isolation and identification of organism with culture usually taking 4-8 weeks. Bacteria can be cultured in egg-based media.
• Guineapig inoculation: Inoculation of material S/C or I/M in the flank or thigh region respectively. The animal is sacrificed in 6^th -8^th week for the presence of an acid-fast organism.
• Tuberculin test: Intradermal inoculation of Purified Protein Derivative (PPD) prepared from the culture of Mycobacterium in the neck or caudal fold. Measurement of the thickness of the skin with the help of a vernier calliper after 72 hours of inoculation.
• Double intradermal test (Stormont test): It is the modification of the intradermal test used for the diagnosis of tuberculosis in field conditions.  
• Earlier confirmatory diagnosis can be done with the help of PCR.   

Treatment:

• Treatment of tuberculosis in animals is more or less similar to that used for human beings.
• Due to the progress being made in the treatment of human tuberculosis with drugs such as isoniazid, a combination of streptomycin and para-aminosalicylic, and other acids, the treatment of animals with tuberculosis has undergone some examination.

 Prevention and control:       

• Eradication of bovine tuberculosis has been virtually achieved in many countries.
• WHO recommended the DOTS (Directly Observed Treatment, Short-course.) strategy to reduce the number of tuberculosis (TB) cases. In DOTS, healthcare workers observe patients as they take their medicine. In India, the DOTS strategy was launched in 1997.