Tuberculosis

Syn: Pearl’s disease

• It is chronic insidious contagious disease of man and animals caused by pathogenic microorganism of genus Mycobacterium.
• Disease is characterized by development of tubercles with resultant caseation and classification. They are frequently located in lungs and lymph nodes.
• These tubercles may also be found in liver, spleen, intestine, peritoneum, meninges, and long bones.
• This disease has been listed as prioritized zoonotic disease of Nepal by Government of Nepal.
• WOAH listed this disease as list B disease.

Etiology:

• There are four types of Mycobacteria which affects domestic animals, birds and human beings.
• Bovine type- Mycobacterium bovis
• Human types- Mycobacterium tuberculosis
• Bird type- Mycobacterium avium
• Vole bacillus type- infects murines
• Organism are slender, slightly bent or straight rods; measuring 0.2-0.6µ x 1.5-4µ
• Bacilli are enclosed in a thin, waxy or fatty capsule due to which they take acid-fast stain. They appear red on staining.

Epidemiology:

• This disease is one of the ancient diseases and worldwide in distribution.
• It is highly prevalent in tropical and sub-tropical countries like Pakistan, Bangladesh and Nepal.
• Disease has been eradicated from Canada, Denmark, Finland, Germany, Great Britian, Switzerland, USA, USSR by elimination positive reactor through tuberculin test.
• It has been declared global emergency by WHO. In 2023, an estimated 10.8 million people fell ill with TB worldwide, including 6.0 million men, 3.6 million women and 1.3 million children
• 5 million of people died of tuberculosis in 1990.
• According to a study in 2013-14, prevalence of bovine TB in cattle were 13.33% while that of buffalo is 14.04%. (Jafar Khan, 2014)
• 8% of cattle were positive by tuberculin test in Kathmandu valley (Tulsi Ram Gompo, Asmita Shrestha, Eliza Ranjit, Bhanu Gautam, Khim Ale, Swoyam Shrestha, Diker Dev Bhatta, 2020)
• Of all domestic animals, cattle are most susceptible and bovine strain is most pathogenic over three strains.
• Incidence is more in pure bred and crossbred cattle.

Transmission:

• Through contact with infected animals or their discharges or morbid tissues
• Through inhalation of droplet discharged by infected animal during coughing.
• Sputum, feces, urine, vaginal discharge, semen, milk, wound discharges may act as good source of transmission.
• Animals can also get infection through ingestion of contaminated feed and water.
• Through contaminated instruments or utensils
• It may be transmitted when animals come in contact with infected people.
• Through act of coitus or through skin
• Through infected semen during process of AI

Factors for transmission:

• Age: younger age of group of cattle are less susceptible whereas higher age group of humans are more susceptible to transmission.
• Malnutrition: malnourished animal easily contacts the infection than well nourished. Vitamin A and Vitamin C deficiency predispose the infection.
• Hygiene: poor sanitation and poor ventilation are contributing factor for entry and establishment of disease.
• Management: Overcrowding house and premises, common drinking and feeding troughs are important source of transmission.

Pathogenesis:

Clinical Signs:

Cattle and buffalo:

• There is slow but continuous loss of body weight.
• Dyspnoea, increased rate of respiration
• Deep, persistent, painful dry, hacking cough
• Percussion on affected areas will produce dull sound.
• Abdominal pain, obstinate diarrhoea, chronic bloat, and emaciation.
• Feces is coated with mucus, pus cells and occasionally blood.
• Rectal palpation reveals enlarged mesenteric lymph nodes.
• In case of uterine infection, purulent caseous discharge tinged with blood.
• Abnormal sexual excitement, irregular estrus cycle, abortion and sterility.
• Swollen and painful testicles in bulls
• In case of mammary gland infection, there is formation of small nodules in mammary tissues. Supramammary lymphnodes are enlarged.
• On progression of disease, milk secretion gradually diminishes and ultimately may completely ceased.
• Milk slowly turn greenish, yellow color, white flakes and curdle mass appear in milk.

CNS Involvement:

• Impairment or loss of vision
• Incoordination of gait
• Epileptic forms of fits
• Partial paralysis
• Hyperaesthesia, occasional circling
• In case of tuberculous joint, there is painful swelling of joint.
• There may be enlargement of prescapular, prefemoral, supramammary and cervical lymphnodes due to tuberculosis.
• When skin is involved, nodules of various sizes appear singly or in group mostly on upper parts of the limbs.

Horse:

• Gradual emaciation accompanied with fluctuation of temperature and capricious appetite.
• Rapid laboured breathing
• Periodic coughing, mucopurulent discharge from nostrils
• Abdominal respiration
• Percussion reveals area of dullness on affected part of lungs
• Lesion may spread to bone leading to disturbances of locomotor system and pain.
• Stiffness of neck and restriction of movement
• Small displaceable nodules under skin. Nodules may rupture discharging purulent materials. Fistula may develop
• Skin changes in extremities appear as greasy heel condition.
• Lymph nodes may become enlarged.
• Working capacity of horse is lost.
• Rectal examination reveals enlargement of mesenteric lymph nodes.

Sheep and goat:

• Signs of bronchopneumonia is cardinal manifestation.
• Coughing, respiratory distress
• Some sheep and goat may develop diarrhoea and ulceration of alimentary mucosa
• Enlargement of lymphnodes
• Fluctuation of temperature

Pigs:

• There is enlargement of submaxillary, pharyngeal, and cervical lymph nodes.
• Lymph glands may rupture with clinical manifestation like distressed breathing.
• Difficulty in breathing, coughing
• Locomotor disturbances in case of bones and joint infection

Dog:

• Dog may remain as asymptomatic carrier
• Pulmonary form of TB is characterized by dyspnoea, tachypnea, chronic cough. Pneumothorax may also develop.
• In extra-pulmonary form, visceral organs are mostly affected. Diarrhoea may be the outcome. Feces may contain blood.
• Liver may be enlarged and painful.
• Skin lesions and discharge of such skin lesions.
• Inappetance and loss of body weight are well marked towards the terminal stage of disease.

Cat:

• Tuberculosis in cat is rare.
• Subcutaneous tuberculous abscess may be formed.
• Inappetance and loss of body weight
• Liver may be enlarged and painful.
• Diarrhoea, feces may contain blood.

PM Findings:

• Tuberculous lesion may affect any tissue or organ in cattle, sheep and goat.
• Tubercle lesion consist of caseous core surrounded by necrotic tissue and entire mass is encapsulated. These lesions are found in lungs, liver, pleura, peritoneum, kidney, spleen and regional lymph glands.
• Caseous portion may become calcified.
• In advanced cases, the affected glands are transformed into large tumor like growth containing thick caseous purulent materials.
• Tuberculous lesion may persist in an animal’s body for entire life span.

Diagnosis:

• On the basis of clinical signs
• Clinical pathology; examination of sputum or other discharge
• Microscopic examination of smear or sputum stained with Ziehl-Neelsen may show acid fast rods.
• Cultural examination: Dorset’s egg media may be used for bacterial culture.
• Tuberculin test; it is important method of diagnosis of bovine tuberculosis. In this method, tuberculin; 4 ml is injected subcutaneously in the neck of cattle produces local reaction at site of injection. A rise of temperature above 40°C at 6-8 hours indicates a positive reactor.
• Single intradermal test: 0.5 ml of tuberculin is injected in the neck or caudal fold and reaction is read between 48-72 hours. Swelling >6mm in diameter and greatly raised indicates positive reaction.

Treatment:

• Treatment of tuberculosis in animals are generally attempted more or less in the same lines as of human treatment.
• Drugs used in human treatment like isoniazid and para aminosalicylic acid have been used with encouraging result.
• Streptomycin sulphate can be used through parenteral route.
• Isoniazid @ 5mg/kg, b.wt. has been found to be beneficial against tuberculosis in cattle. About 1 and half month is required for treatment.
• Administration of isoniazid at the dose level of 10mg/kg, b. wt for a period of 6-12 months has given excellent results in stopping transmission and excretion of bacilli in the milk of cow.
• Oral 300 mg of rifampin and 300 mg of isoniazid along with 500 mg streptomycin IM can be used in goat.

Control Measures:

• A suspected case should be brought under intradermal test to screen it.
• A positive reactor should be segregated and slaughtered. Dead animal should be burnt or buried and slaked lime should be poured over it.
• All the incontact animals above 3 months of age are to be placed under test.
• Doubtful cases should be retested after a month and slaughtered if positive.
• All suspicious cases must be isolated until proved negative.
• Newly purchased animal should be tested before allowing them to mix with rest of the animals in the herd.
• All the animal prior to transportation from one place to another should be brought under testing.
• Premised inhabited by the sick animals should be properly disinfected.
• Feeding trough, watering utensils and milking pans should be thoroughly scrubbed and disinfected.
• In pail fed calves, milk of tuberculous free cows should be offered and milk should be sterilized prior to offering.
• Farm personnel should be periodically tested for tuberculosis.
• Children shouldnot be allowed milk or milk products of tuberculous affected cows.
• Person affected with TB shouldnot be allowed in farm.
• In human, BCG vaccination should be used in childhood.
• DOTS is recommended nowadays in human cases.
• Calves may be vaccinated with BCG.