T.B in cattle, Bovine tuberculosis, Pearl disease, and Cachexia indicate a serious disease with high risks affecting cattle.
Dr.provet preferred to focus on this serious disease through this article.
This article includes:
What's bovine tuberculosis?
Susceptibility to T.B in cattle.
Infection sources of T.B in cattle.
Modes of cattle T.B Transmission.
Pathogenesis of T.B in cattle.
Clinical signs of T.B in cattle.
Postmortem lesions of T.B in cattle.
How to diagnose T.B in cattle?
Control of T.B in cattle.
Control on a herd basis.
Control on area basis:
What's bovine tuberculosis?
It is a chronic contagious disease of cattle characterized by emaciation, enlargement of lymph nodes
and development of caseous nodules in different organs of the body.
This disease is caused mainly by Mycobacterium bovis which is an intracellular Gram-positive aerobic acid-fast bacilli.
This organism has moderate resistance to heat and desiccation, but It is sensitive to direct sunlight, ultraviolet irradiation, and 10% formaldehyde spray and phenolic compounds.
Susceptibility to T.B in cattle
Cattle and buffaloes are more susceptible.
Fattening cattle are less affected than dairy one.
Housed cattle are more affected than cattle at pasture.
Infection sources of T.B in cattle
Infected cattle are the main source of bovine tuberculosis infection; the organism is excreted in:
Exhaled air and sputum.
Milk, feces, and urine.
Vaginal and uterine discharges and discharges from opened peripheral lymph nodes.
Modes of cattle T.B Transmission
The route of infection:
Inhalation (droplet infection).
Ingestion of contaminated food, water, and milk.
Intrauterine infection at coitus or by the use of infected semen.
Intramammary infection may occur through teat siphons or cups of milking machines.
Infection through skin lesions, but is very rare and it is usually limited to localized tuberculosis at the site of infection.
Pathogenesis of T.B in cattle
Droplet infection results in caseous nodules in the lungs and associated lymph nodes. The lesion is called primary complex and calcification commences later.
Infection through ingestion leads to the formation of lesions in pharyngeal or mesenteric lymph nodes.
Spread of infection from the primary complex occurs via blood or lymphatic fluid resulting in military tuberculosis (discrete nodular lesions in various organs).
caseous nod in many organs discharges and discharges from opened peripheral lymph nodes.
The bacilli multiply within phagocytes and the lipid components protect the bacilli, which induces cellular reaction while protein fraction of the bacilli induces hypersensitivity.
Clinical manifestations appear according to the site of localization e.g pulmonary tuberculosis, intestinal tuberculosis, tuberculous mastitis, or tuberculous metritis.
In advanced cases, Tissues of cattle are exposed to large amounts of protein and the animal becomes desensitized.
Then toxemia, which causes debility and death.
The incubation period of T.B
It is two to several months.
The pre-allergic phase is 4-6 weeks.
Clinical signs of T.B in cattle
The diseased animal shows:
Emaciation is a general sign.
Enlargement of superficial lymph nodes.
The respiratory form of T.B includes:
Persistent cough, which occurs once or twice at a time.
In advanced stages, there is dyspnea as a result of the involvement of the bronchial lymph nodes which leads to constriction of air passages.
Digestive Form of T.B includes:
Recurrent or persistent ruminal tympany may occur due to enlarged mediastinal lymph nodes.
Dysphagia and noisy breathing due to enlarged retropharyngeal lymph nodes, pharyngeal obstruction. which causes diarrhea may occur due to tuberculous ulcers of the small intestine.
Genital form of T.B includes:
Tuberculous metritis, Tuberculous vaginitis, infertility, or recurrent abortion at late pregnancy or birth of a calf that dies quickly of generalized tuberculosis.
Tuberculous orchitis may occur.
Tuberculous mastitis includes:
Induration in the upper part of the udder.
Enlargement of the supramammary lymph nodes.
Milk contains very fine floccules, which settle after the milk stands leaving a clear amber fluid.
Postmortem lesions of T.B in cattle
The postmortem examination of the dead carcass shows:
Tuberculous granulomas retropharyngeal and mediastinal lymph nodes.
military abscesses in the lung may cause suppurative bronchopneumonia.
Pus has a characteristic cream to orange color.
Chronic lesions are usually nodular and contain caseous material.
The lesions are usually calcified and surrounded by fibrous capsules.
Generalized cases (Military tuberculosis) are characterized by shot-like lesions in many organs as tuberculous lesions of the liver.
How to diagnose T.B in cattle?
The disease can be diagnosed through:
Clinical signs and postmortem lesions.
Laboratory diagnosis by tuberculin test.
Differential diagnosis
The disease confused with:
Diseases causing enlargement of lymph nodes:
Actinobacillosis.
Bovine leukosis.
Theileriosis.
Diseases causing respiratory signs:
Lung abscesses.
Chronic contagious bovine pleuro-pneumonia.
Mastitis and Metritis.
Bovine farcy:
It is an infectious disease of cattle and buffaloes caused by Nocardia farcinica characterized by purulent lymphangitis and lymphadenitis with pulmonary signs.
The tuberculin test gives positive results for bovine farcy, so the film from unopened nodules should be done to differentiate between them.
Skin tuberculosis:
It is characterized by nodules along the course of corded lymphatics under the skin on the lateral aspect of the forelegs and shoulder.
Edematous skin disease:
It is an infectious disease of buffaloes and cattle caused by corynebacterium ovis characterized by ski nodules and abscessation of regional lymph nodes.
Control of T.B in cattle
Tests and slaughter are still applied for the control and eradication of tuberculosis.
Control on a herd basis:
It mainly depends on:
Detection and removal of infected animals:
It can be occurred through:
All animals over three months of age should be tested using the tuberculin test and culling of positive cases.
Doubtful cases should be retest after two months. The herd should be retested at three months intervals until a negative test is obtained.
A further test is conducted six months later and if the herd is again negative, the herd may be classed as free of the disease.
Prevention of spreading of infection
This step can be occurred through:
Proper disposal of caresses, aborted material, vaginal and uterine discharges by burning or burial using lime.
Cleaning and disinfection of feed and water through the use of 5% phenol.
Attendants should be checked regularly.
Avoid overcrowding and bad ventilation.
Calves should be fed on tuberculous-free milk.
Replacement animals should be done from tuberculosis-free herds tested and retested after two months.
Control on area basis:
This wider step is so important to control the spreading of T.B in cattle, including:
Determination of the incidence using the tuberculin test.
Eradication should be carried out firstly in herds and areas that have a low incidence of the disease.
BCG vaccine has many disadvantages:
Vaccination is carried out by S/C injection of 50-100 ml vaccine.
Large swelling appears at the site of injection.
Intravenous BCG injection causes severe systemic reactions.
Vaccination must be repeated annually.
A vaccinated animal remains positive to a tuberculin test.
Calves must be vaccinated as soon after birth and give immunity not more than 6 weeks and immunity not strong.
Treatment of T.B in cattle
Chemotherapy of tuberculosis in domestic animals is of little value because of:
The chronic nature of the disease.
The high costs.
Ineffective nature of treatment because microorganisms are surrounded by vascular capsulated connective tissue.
The disease has zoonotic importance.
Finally, bovine tuberculosis (T.B in cattle) is a terrifying zoonotic disease that must be well controlled, its transmission to humans is that will be addressed in the next article.
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