Avian Tuberculosis

Avian Tuberculosis

Aditya Sharma¹, Sheikh Uzma Farooq², Akashdeep Jalandhari³, Muskan⁴, Deepak Mahajan⁵

¹Department of Veterinary Pathology, Khalsa College of Veterinary and Animal Sciences, Amritsar

²Department of Veterinary Pharmacology and Toxicology, Khalsa College of Veterinary and Animal Sciences, Amritsar

^3,43^rd Prof Student, Khalsa College of Veterinary and Animal Sciences, Amritsar

⁵Department of Livestock Products Technology, Khalsa College of Veterinary and Animal Sciences, Amritsar

Introduction:-

Avian mycobacteriosis in poultry is a contagious disease and may also be called avian tuberculosis or avian TB. Several mycobacterial species can be involved in the aetiology of avian tuberculosis. However, avian tuberculosis is most often caused by Mycobacterium avium belonging to serotypes 1, 2, 3 and 6. The capacity of M. avium to produce progressive disease may be related to cell wall constituents and certain complex lipids present in the cell wall such as cord factor, sulfur-containing glycolipids or strongly acidic lipids. In the spread of infection the most important source of the organism is the infected bird; and secondarily, because of the prolonged survival of M. avium outside the body of the host, items contaminated with the droppings of such birds. These usually include litter, contaminated pens and pasture, equipment and implements which come into contact with infected fowls, and the hands, feet and clothing of attendants. Clinical signs are not pathognomic and vary depending on the organs involved. Mortality over a short period may be insignificant but the intermittent loss of adult birds in valuable breeding stock and decreased egg production in layers are detrimental. Avian Mycobacteriosis also has zoonotic importance and commonly affect the immune-compromised human. The various preventive and control measures are present to control this disease but the diagnosis of the disease is difficult and hence it remains uninvestigated in many parts of our country.

Transmission:-

Susceptible chickens are primarily infected by ingesting or inhaling aerosolized Mycobacterium from a contaminated ground surface. Infected birds shed the organism in their droppings, where it can survive in the soil for months to years. There will be higher concentrations of the bacteria in areas which previously or currently house high populations of birds, living in unhygienic conditions. Wild birds, pigs, and certain mammals can act as significant reservoirs. Rodents can also be carriers of the bacteria, transmitting it through their feces to the environment.

Signs:-

The condition is usually chronic and symptoms may continue over a period of weeks or months before death. There is usually progressive but slow loss of condition, loss of energy, and increasing lethargy. Although appetite remains good, there is eventually gross emaciation with marked atrophy of the sternal muscles.The “keel” becomes prominent or even “knife edged”. The face and comb become pale.

Most frequently observed clinical signs include:

1. Loss in condition: The chicken may progressively experience a loss in body condition. Resulting in moderate to marked loss of pectoral muscle mass and develop a prominent keel.
2. Loss of body fat causes sinking of the eyes within the orbits, making the chicken’s face appear smaller than normal. They will have a low body condition score. However, due to the weight of the granulomas that form inside their bodies, body weight alone is not a reliable form of distinguishing whether a bird has lost weight.
3. Poor quality feathers: Affected chickens may have a delayed molt and preen less often, resulting in dull and poor-quality feathers.
4. Diarrhea: When the intestines are involved, chickens may have persistent diarrhea and frequently stain their vent feathers with feces.
5. Pale comb/wattles: The chicken’s face, comb, wattles, and earlobes often become dry, pale, thinner, and occasionally have bluish discoloration.
6. Abdominal enlargement: Chickens may present with marked caudal coelomic distension, with a very firm mass or fluid (ascites).
7. Abnormal gait: Some chickens may develop bone lesions, causing lameness or stiffness, and walk with a peculiar jerky hopping gait.
8. Difficulty breathing: If chickens develop granulomas and lesions in their lungs, or abdominal enlargement, it can interfere with their breathing.

9.Subcutaneous lesions: Localized infections are generally the result of traumatic injuries that inoculate environmental mycobacteria into lesions. They are rare, and often present as nodular, ulcerated, fistulous draining tracts or nonhealing granulomatous or pyogranulomatous wound infections which do not respond to conventional drainage and antimicrobial therapy.

Post mortem findings:-

• Grossly, the lung and costal membrane contained numerous grayish-white masses ranging from 0.1–0.2 cm in diameter a long the inner surface of the thorax, single or multiple subserously prominating tubercles were
• The liver and spleen are usually grossly enlarged and sometimes rupture, with resultant blood in the body cavity. The smaller tubercles in these organs can be easily enucleated from the surrounding tissue.
• Protrusion 0 f tubercles from surface 0 f the spleen, gives spleen an irregular, “knobbly” appearance.
• The bone marrow of the long bones of the legs usually contains tubercular nodules. These can be best seen grossly if the bones are split longitudinally, particularly in the region of femoro-tibiotarsal and tibiotarsal-tarsometatarsal joints. They are pale yellow in colour, and vary in size and number. This is one of the characteristic features of tuberculosis in the chicken.
• These masses were scattered throughout the thoracic cavity and bulged from the underlying

surface.

• The inner surface of the peritoneal cavity was almost totally loaded by similar granulomatous lesions. This was found to be studded with whitish but fray nodule however, without any mineralization.

Microscopic findings:-

• Microscopically, the tubercle is a closely packed collection of pale-staining cells with vesiculated nuclei.
• These epithelioid cells are derived from fixed tissue elements known as histiocytes. The histiocytes phagocytose tubercle bacilli early in the process.
• The cellular mass or “primary tubercle” gradually expands as histiocytes proliferate at the periphery. Within 3-4 weeks, signs of degeneration can be seen in epithelioid cells in the central zone.
• The degeneration is partly due to the avascularity of the cellular mass, and partly to the toxic substances of the tubercle bacilli.
• As the cellular mass becomes larger, epithelioid cells have tendency to fuse and form syncytia. Outlines of the individual cells become less distinct, or disappear.
• This is followed by a necrobiotic change resembling coagulative necrosis. Nuclei of epithelioid cells become pyknotic and may disappear.
• The cellular mass, except the peripheral portion, becomes fused and stains deeply with eosin. The necrotic bacilli multiply and appear singly or in clumps throughout the necrotic tissue.

Diagnosis :-

• History: If the chicken lives in an enclosure where avian tuberculosis was detected or suspected in other birds or previous flocks who lived there. Blood tests: A CBC and blood chemistry may be helpful, depending on where the mycobacterial granulomas develop in the bird. Mild anemia with leukocytosis and a heterophilia and monocytosis may be seen in infected birds. Blood chemistry revealing an elevated AST, bile acids, or CK.
• Intradermal skin test: Also referred to as the tuberculin test. The test involves giving an intradermal injection of 0.03-0.05 mL of purified protein derivative tuberculin into one of the chicken’s wattles or their comb. A positive reaction is indicated by the presence of the inflammation and swelling of the comb or wattle after a 48 hour duration.
• Fecal test: Mycobacterium can sometimes be detected from fecal samples from infected birds. However, repeat culture examinations are required over a course of several consecutive days. The amount of Mycobacterium shed in the feces of infected birds also depends on the stage of infection and organs affected.
• Necropsy: Gross necropsy findings and histopathology may reveal characteristic lesions, and tissue cultures which confirm the presence of Mycobacterium. Granulomas (multifocal to miliary nodules, ranging in size from microscopic up to about 4 cm in diameter) in affected organs are the most common finding in chickens with avian tuberculosis. The organs most frequently affected include the spleen, liver, intestines, lung, and bone marrow.

Prevention:-

1. Minimize stress – There is a correlation between stress and enhancement of the disease. Reduce contact with wild birds and pigs. As for poultry, stress may play an important role in allowing a subclinical infection to develop into full-blown disease hence efforts should be made to mitigate against other stressors such as poor nutrition, pollution, con-current infections, disturbance etc.
2. Don’t house your flock in an area that was previously used to house large concentrations of birds.
3. Maintain good sanitary conditions by cleaning feces regularly.
4. Periodically expose ground surface to sunlight, since the unprotected organism is killed by direct sunlight.
5. Provide vitamins and probiotics to diet to help immune system.
6. General standards of personal hygiene are sufficient to reduce risk to most humans in and around wetlands and infected animals.

Conclusion:-

In most situations, the disease is likely to have relatively limited impact on wildlife other than as an occasional cause of death. The greatest impact is on poultry flocks where control actions involve culling. Public health concerns are relatively limited although care should be taken if it is known that infection is present, to reduce potential for opportunist infections. High risk (e.g. immunocompromised) individuals should take extra precautions in such situations. Where the disease is diagnosed in industrial units, and culling, cleansing and disinfection measures are required, economic losses can be significant. Within smaller flocks the loss of production and general unthriftiness of animals is of importance.

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