EVOLUTION

ANIMAL BREEDS

DISEASES

MEDICATIONS

FOOD/FEED

BEHAVIOUR

EXOTIC ANIMALS

SPECIAL SECTION

Bacterial Disease - Tuberculosis

Synonyms:

Consumption, Pthisis, Pearl's disease and Scrofula

Etiology

As based on species of genus mycobacterium, affecting animals, human and birds, it is classified majorly into four types:

  • » Bovine type: Animals and human.
  • » Human type: Human and animals.
  • » Avian type: Fowls, pigs, horses and dogs.
  • » Volebacillus: Murrines species.

Different species of mycobacterium affecting different animals and human beings.

  • » Cattle: M.bovis and M.tuberculosis.
  • » Human - M.tuberculosis and M.bovis.
  • » Horses: M. bovis (majorly), M.tuberculosis and M.avium.
  • » Dogs: M. bovis, M. tuberculosis and M. avium.
  • » Pigs: Bovine, human and avian type.
  • » Birds: M.avium.

Prevalence of infection

Tuberculosis is prevalent worldwide both in animals and human beings.

TB is endemic in India both in animals and human beings.

Predisposing factors

Overpopulation in small area.

Purely intensive rearing.

Inter current infection.

Poor sanitation.

Inadequate ventilation.

vitamin A and C deficiency.

Young age groups and malnourishment.

Source of infection

Exhaled air, feces and infected meat.

Nasal discharge, sputum and tracheal mucus .

Contaminated inanimate and animate objects .

Reproductive discharges .

Feed, water and soil.

Reservoirs and carriers of infection

South West England: Badgers (Meles Meles) - During their nocturnal visits in the farm buildings, excrete organism through urine and cattle in the same premises pick up the infection.

New Zealand : Brush tailed possum (Trichosarus vulpecula)- Cattle infected when get along with possums in pasture.

North America : Mule deer (Odocoileus hemianus), whilte tailed deer, elk, (O. viriginianus and Cervus elaphus Canadensis), Bison ( Bison Bison).

Great Britain : Red deer is playing very important role.

South Africa : Buffaloes (Syncrus caffer) and water buffaloes (Bubalis bubalis) acts as maintenance hosts.

India: Infected animals and human being acts as source of infection.

Transmission

Nasal discharge and tracheal mucus.

Ingestion: Communal use of feed and water troughs.

Ingestion of tuberculosis infected animals milk and their products.

Direct contact with infected animals.

Inhalation of droplet nuclei from aerosol.

Congenital infection by vertical transmission.

Host affected

Cattle are the primary host highly susceptible for the infection.

Pure bred and cross bred are highly affected as compared to zebu cattle.

Sheep and goats more or less resistant to infection.

Badgers, possums, pigs, dogs, primates, large cats and elephants other than cattle are affected and act as maintenance host.

Infected cattle are the main source for human infection..

CLINICAL SIGNS

General form

Affected animals become docile, lethargic but seem to be bright and alert.

Cows with prominent miliary tubercle lesions are clinically normal.

Progressive emaciation.

Capricious appetite, fluctuating body temperature and rough / sleek hair coat.

In spite of good appetite animal does not put up weight.

All these general signs are pronounced following calving.

Respiratory form

Silent or paroxysmal cough especially during early morning and chilled weather.

Chronic cough due to bronchial pneumonia.

Rapid respiration with dyspnoea revealed by auscultation and percussion of the chest due to enlargement of bronchial lymphnode and obstruction of air ways.

Squeaking crackles are audible but noise audible over the caudal lobes.

Enlargement of retropharyngeal lymphnode causes dysphagia and noisy breathing due to pharyngeal obstruction.

Reproductive form

Metritis and inflammation of placenta leads to infertility, abortion and failure in conception.

Nervous signs.

In horse painful cervical osteomyelitis causes stiffness of neck and difficulty to eat.

Sheep and goats

Bronchopneumonia and terminal dyspnea.

Intestinal ulceration with diarrhea which is rare in cattle.

Enlarged lymphnode of alimentary tract.

Kids more progressive to early death.

Pigs

TB lesion is cervical lymphnodes.

Horses

Cervical vertebrae show osteomyelitis, and causes stiffness of neck.

Zoonosis

It is an important zoonotic disease. There is an increase incidence with an increase spread from animal to human.

M. bovis is responsible for 5-10% of human tuberculosis. Children getting infected via drinking of infected breast milk.

NECROPSY FINDINGS

Cattle, sheep, goats

Granulomatous lesion in bronchial, retropharyngeal AND mediastinal lymphnodes.

Firm and enlarged pharyngeal lymphnode, swelling in dorsum of the pharynx.

Miliary abscesses in lung.

Pus is characteristic creamy and cheesy.

TB nodule present in pleura and peritoneum.

TB lesions are covered with fibrous capsule.

Lesions in placenta with chronic purulent material.

Orchitis.

Enlargement of supramammary lymphnode - TB lymphomatosis.

Chronic lesions

Discrete, nodular, thick yellow to orange caseous material followed by calcification covered by a thick fibrous capsule.

Pigs

Enlarged miliary TB localized in tonsils, submaxillary, cervical, hepatic, bronchial, mediastinal, mesentric lymphnode with white caseous calcified material surrounded by a strong fibrous capsule.

Horses

TB lesion in intestinal wall, mesenteric lymphnode and spleen.

Cut surface of the LNs appears fleshy and resemble neoplastic tissue.

Mineralisation and tissue necrosis noticed.

DIAGNOSIS

Based on clinical signs and necropsy findings.

Palpation of supramammary lymphnode essential for suspected TB mastitis cases.

Isolation and identification of organism by culture or acid fast staining.

The following are the tests for detection of cell mediated immunity.

Single intradermal test

PPD injection is given at caudal fold at base of the tail in sheep and goats / lateral center portion of the neck in cattle is highly sensitive.

Initial skin thickness measured with a Vernier Caliper.

DOSE: 0.1 ml herds with unknown status of sensitivity.

0.2 ml herds with known infected herds.

Final skin thickness and inflammatory changes at 72 hours post injection should be taken.

Increasing skin thickness more than 4mm is taken as positive.

Short thermal test

Intradermal tuberculin 4ml injected s/c in the mid neck of cattle.

Initial rectal temperature 39 ° C (102 ° F) at the time of injection.

If the temperature increase in 4, 6, 8hrs to above 40 ° C animal is classed as positive reactor.

Stormont test

First intradermal injection of 0.1 PPD at middle of the neck followed second injection should be given 0.1 after 7 days at the same site.

Increase in skin thickness of 5mm or more at 24 hrs after this second injection is considered positive.

Cattle with M. avium does not give positive reaction but skin TB cases do.

It is more accurate than SID.

Comparative test

For testing the animals for TB, along the side of PPD tuberculin injection, 12cm apart, M.avium PPD should be given and the test result should be compared.

Test results read after 72 hrs.

This test is not used for initial screening.

But can be used as a primary test when there is a high incidence of Avian TB and JD.

Gamma Interferon Assay

This test measures the amount of gamma interferon released from the antigen stimulated whole blood cells.

Elisa for detection of antibody.

Molecular diagnosis by PCR.

Sputum, feces, milk, blood and tracheal secretions must be collected for the diagnosis.

Differential diagnosis

Lung abscess.

Pleurisy.

Pericarditis.

Traumatic reticulitis.

Chronic contagious bovine pleuropnemonia.

Upper respiratory tract infection.

Actinobacillosis

Bbovine leukosis.

Lymphadenopathy.

Mastitis.

TREATMENT

There is no antibiotic treatment succesful in control tuberculosis.

Supportive treatment to enhance the immune response can be done.

Prevention

All animals over six months and above should be tested by tuberculin test.

Positive reactors disposed of according to local legislation.

Suspicious cases must be retested by comparative test.

Retesting: If incidence is higher, retesting should be done in 45-60 days after desensitization of intradermal injected animals.

Annual testing of all cattle, quarantine, test positive herds should be slaughtered .

Identification of individuals and wild life reservoir.

BCG vaccination is available for calf hood vaccination. But vaccinated animals react positive to the skin test. Immunity is not strong and long lasting .

Most probably cell mediated immunity is predominant.

Accredited areas set up : All cattle in this area are tested and reactors removed and monitored until next generation off-springs become free from infection by tests.

Control

Disinfection of utensils with 5% hot phenol and cresol.

Feeding of calves with milk free from infection.

Test and introduce new stock.

Education public about the significance of the disease.


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