Tuberculosis is an infectious, bacterial, contagious disease affecting humans and many other animal species. It is characterized by its chronic evolution and high polymorphism. It is identified by inflammatory lesions in the form of nodular granuloma known as tubercles.
Significance
Hygienic
It is a major zoonosis. It is however important to distinguish zoonosis tuberculosis caused by Mycobactérium bovis from interhuman tuberculosis caused by Mycobactérium tuberculosis, which is responsible for most of human tuberculosis cases.
Economic
It is a threat to cattle farming as it causes losses in milk production, carcass and offal depreciation (abattoirs harboring the disease are seized), stunted growth and fattening, reproduction disorders, loss of young animals and leads to export embargo.
Declared to the OIE en 2004 by the following countries: Argentina, Bolivia, Brazil, Canada, Chili, Columbia, Costa Rica, Cuba, Dominican Republic, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, USA, Uruguay and Venezuela.
All domestic and wild vertebrate species including man who can become infected by tuberculosis bacilli.
Tuberculous bacilli are germs from the Actinomycetales group, from the family Mycobacteriaceae, Mycobacterium genus.
They include numerous species. Some are ubiquitous and highly resistant and others are apathogenic, while others are pathogenic for humans and animals. This makes diagnosis difficult.
Mycobacterium bovis is made up of a rudimentary pseudomycelium forming small, static bacilli which are strict aerobes and resistant to acid-alcohol solutions. The ideal growth conditions for the bacilli are: T° = 37°C, pH = 6-6, 5.
• Mycobacterium bovis: is the agent responsible for bovine tuberculosis.
It affects bovines and other herbivores but also cats and to a lesser degree, dogs and humans.
• Mycobacterium tuberculosis: is the agent responsible for human tuberculosis. It affects man, dogs and to a lesser degree, cats, ruminants and ornamental birds.
• Mycobacterium avium: is the agent responsible for tuberculosis in birds and largely contributes to pig tuberculosis.
Slow, chronic progression over several months or even years. Acute phases aggravate progression.
Symptoms go unnoticed for long periods where the tuberculous animal appears to be in perfect health. At the end of progression general health is affected but there are few characteristic signs.
Incubation period: long, more than 2 months.
General health:
• Young subjects: retarded and unstable growth, sickly appearance
• Adults: poor general condition in severe cases (exhaustion, wasting, muscular atrophy, dull fur, weathering, diarrhea, cachectic, increase in T° prior to progression, progressive anorexia, interrupted rumination, death)
Other symptoms: no other characteristic symptoms apart from specific local signs.
• Pulmonary: are the most frequent symptoms (in 80% of cases). Asymptomatic followed by breathing difficulties, coughing, fetid, yellowish discharge.
• Intestinal: Very rare. Asymptomatic or chronic enteritis.
• Mammary: in the advanced stages, hypertrophy, hard, lumpy appearance.
• Genital: chronic metritis in females, orchitis in males.
These four locations are the most dangerous in terms of transmission. Tuberculous bacilli are massively excreted in discharge, milk, faeces, semen and pus.
• Other locations: serous membranes, liver, spleen, lymph nodes (tracheobronchial, retropharyngeal, especially mediastinal lymph nodes), bones, meninges, muscle. Constant tuberculous adenopathy.
Treating animal tuberculosis is both hazardous and dangerous and should be proscribed. Treatment would be costly with unpredictable results. The use of antimycobacterial products in animals would above all impose the risk of selecting resistant germs highly dangerous for human health.
Necessary for two reasons:
- Hygiene: to eliminate sources of contamination for man
- Economic: reduce losses for farmers
Several countries are aiming to eradicate the disease with simultaneous action for "tuberculosis infection" and the "tuberculosis disease".