Veterinary Article

BOVINE TUBERCULOSIS : A PROGRESSIVE DISEASE

(1) Dr. Rabyia Javed, Ph.D Scholar
Department of Veterinary Microbiology, GADVASU, Ludhiana, Punjab
(2) Dr. Rakhi Gangil, Assistant Proffesor
Department of Veterinary Microbiology, College of Veterinary Sciences and AH Mhow.

Introduction

Infectious diseases are one of the major reason for the economic losses in the dairy sector. “Bovine Tuberculosis” causes great economic losses and poses an enormous public health threat as well (O’Reilly and Daborn 1995). Mycobacterium complex that is commonly concerned with causing the disease in domestic animals and man, out of only which M. bovis is known to produce progressive disease in cattle and buffaloes. The human and avian types of tubercle bacilli are responsible only for retrogressive lesions in the bovine species and are important for the nuisance they create in the pursuit of control program, by bringing about tuberculin conversion of healthy individuals. This interferes with the detection of actual disease and the tracing of source of infection in a herd. Bovine Tuberculosis caused by Mycobacterium bovis (M. bovis) has no geographical boundries and infection occurs in diverse group of animals,which includes farm animals of economic importance ,wild life and humans (Grange 2001; Pavlik et al., 2002). The bacteria that cause bovine TB, called Mycobacterium bovis, are closely related to M.tuberculosis, the bacteria that usually cause TB in' humans. It has been included in the List B diseases of office internationale des epizooties ( OIE ) ( OIE 2008 ).

CHARACTERSTICS

The organism does not grow on blood agar plates and requires 6-8 weeks of incubation time to see visible growth on Lowenstein-Jensen media. Acid fast staining would yield acid fast positive rod shaped organisms on sputum smears. The tubercle bacillus is about as susceptible to the action of heat and light as any other vegetative organism; but is highly resistant to the action of chemical substances. The organism can also survive for long periods in shady places , particularly if protected from light by crust formation on infective discharges or dung.

ROUTES OF INFECTION

1) Respiratory route:- It is the most common (about 90%) and is brought about by inhalation of droplets expelled by a patient during coughing, sneezing etc. Also, the larger infective particles which settle in the upper respiratory tract of the host are normally expelled by the action of the ciliated epithelium and coughed out.

2) Alimentary route:- this route comes into play in case of suckling calves or in young stock fed on raw milk.

3) Congenital :- infection is rare and occurs if generalization of the disease is in mother, involving the uterus, takes place during latter stage of pregnancy.

MODE OF SPREAD IN THE BODY:-

• Lymphatic spread

• Hematogenous spread

Clinical signs:

In the early stages, there are no clinical signs. In advanced stages cattle have:

• Fluctuating temperature

• Anorexia and loss of body condition

• Enlarged lymph nodes

• Persistent cough progressing to dyspnoea and increase in respiratory rate.

Post-mortem findings

M. bovis mainly enters the body via the respiratory tract or the alimentary tract, with the former being the most common. In the lungs localised bronchiolitis is followed by 'tubercle', formation -an abscess with necrotic focus and caseation and sometimes calcification surrounded by a fibrous capsule. Tubercles have a
yellowish appearance, and a caseous consistency.

Differential diagnosis

• Contagious bovine pleuropneumonia

• Inhalation pneumonia

• Traumatic pericarditis

Specimens required for diagnosis

Diagnosis in the live animal is based on skin testing – intradermal tuberculin testing - and clinical examination.
Diagnosis at slaughter is based on identifying typical lesions. It may not always be possible to distinguish tuberculosis lesions from other granulomas and neoplasms grossly. Histological examination in the laboratory, special staining of smears, and culturing of the organism can be undertaken.

References

1. O’Reilly, L.M. and Daborn, C.J. (1995): The epidemiology of Mycobacterium bovis infections receptor and show a distinct tissue distribution and in animals and man - a review. Tuber. Lung. Dis.,surface phenotype. Int. Imm., 1:540-545. 76:1–46.

2. Grange, J.M. (2001): Mycobacterium bovis infection in human beings.Tuberculosis, 81:71-77.

3. Pavlik, I. et. al. (2002): Incidence of bovine in wild and domestic animals other than cattle in six Central European countries during 1990- 1999.Veterinary Medicine Czh., 47:122-131.

4. OIE Manual of Standards for Diagnostic Test and Vaccines (2008): Bovine Tuberculosis OIE, J.Vet.Res., 61:86-89. Paris, pp 683-697.