Tuberculosis is a chronic infectious disease caused by bacteria of the genus Mycobacterium, which appear as characteristic feature being immobile, non-spore and acid-resistance.
This disease has been eradicated in developed countries. In other countries where the disease has decreased Classic, the disease is caused by atypical mycobacteria. Infection levels of bovine tuberculosis in the national herd is estimated between 3% to 4%.
Mycobacteria are widely distributed in nature, ranging from saprophytic, pathogenic and opportunistic pathogenic strictly.
Tubercle bacilli are classics:
M. tuberculosis (Male)
M. bovis (Bovine)
M. avium (Aves)
Also included in this group Mycobacterium microti, which unlike the above does not affect humans but in rats produces tuberculosis.
From 80% to 90% of the transmission occurs via Airborne; with cough or expiration of an infected animal are expelled large amount of microdroplets containing the bacteria which when inhaled by another bovine respiratory system reach ushering reinfection. This is fueled by the daily contact of cattle grazing, feeders, pens and milking parlors.
Another route of entry is the gastrointestinal by eating food contaminated pastures and nasal secretions, feces and urine containing the causative agent.
The digestive tract is important in calves fed with raw milk from sick cows because 1% to 2% eliminate infected cows milk microorganism. Other unusual but probable pathways are: dermal, and congenital genital.
Management factors, age and nutrition are crucial to the route of infection, and in the incubation period of the disease process and dissemination.
From the gateway bacilli are found in the primary complex of regional lymph nodes, then spread via the lymphatics to the lymph node chain. Then there is the spread through the blood to parenchymal organs finally the organism is eliminated in exudates and secretions of infected organs.
The elimination of Mycobacterium bovis by infected animals is intermittent and not in relation to the degree of infection present. It has been shown recently infected animals eliminate the microorganism in the early stages of the disease when sometimes they are not detected by diagnostic tests.
Symptoms are little manifestos in cattle, but some may occur. The route of entry of M. bovis and location of the lesion are closely related in this disease.
The lesions may be located in different organs and lymph nodes, in the form of nodules or tubercles cheesy pus-yellowish vary in size and quantity.
The diagnosis of tuberculosis in infected herds cousin is done by macro and microscopic characterization of lesions in animals that die on farm or sent to slaughter, followed by isolation and characterization in the laboratory.
In endemic areas the diagnosis is made before the animal dies dermoreaccin also be done surveillance in slaughterhouses and make macro and microscopic evaluation of lesions compatible with tuberculosis.
Injuries can vary depending on the anatomical location and manner of spread.
* Generally the lung is finding sizeable areas with caseificada appearance and mineralization zones.
* In the serous surfaces including capsules bodies firm nodules observed smooth surface, varying from 2 to 10 inches in diameter. Caseificadas areas may also occur in the deep areas (Tuberculosis pearl).
* Granulomatous appear firm nodules with areas of caseation and calcification in lymph nodes and parenchymatous organs such as the liver and kidney.
* Purulent exudate in meninges appearance
* Spotlights very small less than 1 cm in diameter in any organ (miliary TB).
In any of the ways presented tuberculosis, this is characterized by the formation of granulomas.
It can detect acid-fast bacilli free in the cytoplasm of macrophages, histiocytes and giant cells in the granulomatous lesions.
The classical method for the detection of bovine tuberculosis is the tuberculin test.
* Single cervical tuberculin test
In this test the inoculation site is the middle third of the neck. This area should shave with machine or scissors to 5 cm. in diameter. Is measured with a thickness gauge previously skin and inject 0.1 ml of bovine tuberculin PPD one milligram per milliliter.
The reading is done using a gauge for 72 hours (about 6 hours). When the reading is impeded due to weather or other causes, this can be up to 24 hours later. If the reading is done later than this, the test is invalid so the diagnosis is not reliable and should be repeated after 60 days.
Positive: 3mm or greater
Negative: less than 3mm
* Year-flow tuberculin test
This test is performed in the year-caudal fold to about 6 cm. the base of the tail and in the center of the fold. This area is less sensitive to tuberculin skin of the neck. Inject 0.1 ml of bovine PPD of a milligram per milliliter.
The reading is done using a gauge for 72 hours (about 6 hours). Positive: 5mm or greater
Suspect: 3mm / 5mm or so
Negative: less than 3mm
Keep in mind that any animal suspected in an establishment where animals are detected positive reactors in past or that is being done is to be considered positive.
* Comparative tuberculin test
The intradermal test was used for comparative embodiment of a differential diagnosis between Mycobacterium bovis infected animals and those sensitized to tuberculin by exposure to other mycobacteria. Such awareness can be attributed to the high antigenic cross-reactivity between mycobacterial species and other related genera.
This test involves the injection of bovine tuberculin and avian tuberculin in different parts of the neck and the subsequent evaluation of response after 3 days.
For this comparative test tuberculin dose should not be less than 2,000 IU of bovine tuberculin or 2.00 IU of avian tuberculin. The distance between both injections should be approximately 12 to 15 cm.
Positive: 4mm larger than avian tuberculin
Doubtful: 1 to 4 mm greater than the avian tuberculin
Negative: when no reaction or when the reaction is equal to or less than the avian tuberculin.
In all the injection is performed by inserting the needle obliquely into the deeper skin layers and injecting the dose of tuberculin. After checked that the injection has been detected on the touch either a small swelling in the place thereof.
Mycobacteria are acid-fast bacilli not spore formers and non-enveloped, so that in the Ziehl-Neelsen staining was observed as bright red bacilli on a blue background.
These microorganisms are obligate aerobes that grow on simple synthetic means, but for the primary isolation from clinical specimens requires a more complex with a base such as potato and egg Lwestein-Jensen medium or an agar base and Middlebrook serum as the medium.
The cultivation is done at 37 C with an atmosphere of 5-10% CO2, growth is slow and lasts 3-6 weeks to develop, the colonies are small, dry and scaly.
Control and eradication
Detection and removal of all infected animals, these motion control, surveillance and dermoreaccin slaughterhouses, and outreach campaigns.