Avian Tuberculosis

Spleen with Avian TB nodules.
Spleen from an ex commercial layer with Avian TB nodules.


Avian TB


Mycobacterium avium. Classification is complex. The 4 subtypes are:-

M.avium subsp avium1,2,3virulent for birds + pigs, rabbits, mink
M.avium subsp hominissuis4-6, 8-11, 21external environment, dust, water, soil – invertebrates and some virulent for birds
M.avium subsp paratuberculosisruminants and other animals
M.avium subsp silvaticumrare, virulent for birds


M.avium subsp avium is an acid fast organism when stained by the Ziehl-Neelsen method. They are highly resistant organisms that can survive in the environment for years. Viable organisms have been recovered from litter and soil 4 years after removal from an infected flock. It has also been shown to survive in sawdust for 168 and 244 days at 20oC and 37oC respectively.


Many Avian species – chickens>ducks>geese>turkeys and also pheasants, birds in zoological collections and cage birds. Pigs and rabbits are also susceptible. Man – infection rare as man considered to be very resistant but it can occur after immunosuppressive disease.)


Close contact with the live or dead bird, ingestion of faeces or faecal aerosols, contaminated ground and equipment. Bacteria have been found in eggs but there is no evidence to suggest that chicks hatched from infected eggs develop the disease. Eggs are unlikely to be the route of infection for a flock.

Clinical signs

The disease has a long incubation period. Therefore, it is usually seen in birds 12 months or older. Loss of condition with birds taking weeks to months to die. Continual low mortality and lost egg production. Appetite may remain good despite cachexia. Disease is commoner in extensive systems and zoos where birds are kept for more than a year. the skin may be pale and comb may be small shrunken. Lameness can be associated with bone infection. Diarrhoea with soiling of the vent feathers can be indicative of intestinal lesions. No specific egg abnormalities but the hen will stop laying.

Spleen with Avian TB lesions cut open.
These lesions of Avian TB in the spleen were seen in susceptible rescued commercial layers placed on contaminated ground


Very poor condition with tubercular granulomata which are variable sized, irregular grey to white nodules that can be found in the liver, spleen, intestine and bone marrow. When cut the granulomas are firm, with pale yellow caseous centres, sometimes bile stained in the liver and intestine. Confirmation of the diagnosis can be made by staining impression smears with Ziehl-Neelsen method.


the history, clinical signs and post mortem lesions are suggestive of the diagnosis. Confirmation of the species of acid fast bacteria should be undertaken by culture or genetic identification. The tuberculin test is available for poultry with avian tuberculin (0.05 – 0.1ml) being injected into one wattle (use a 1cm, 25g needle) and 48 hours later the prescence of swelling and heat being compared with the uninocculated wattle. This test will detect about 80% of positive birds and can miss birds with severe lesions. A stained antigen, whole blood agglutination test and an ELISA test are also available. As none of these tests will detect 100% of infected birds they will need to be used in planned monitoring programme.

Differential diagnoses

Marek’s disease, impactions, coccidiosis, other tumours, other coause of lameness


There is no specific treatment and avian mycobacteria are particularly antibiotic resistant.


Control is by testing birds – PCR or Z-N staining of faeces, tuberculin test (wattle in the chicken), agglutination and ELISA tests. Remove identified carriers. Good hygiene and management and the placing unifected stock on clean groher concentration than that used for disinfecting aganst NDV or AI.

Erysipelas is the 17th commonest diagnosis made by my local AHVLA labs. Details of species affected, clinical signs and post mortem lesions observed can be found by clicking here.

About David Parsons 19 Articles
David Parsons began his veterinary career in mixed practice which triggered his 39-year passion for poultry. Following positions as a veterinary research officer in the Poultry Department at the government’s Central Veterinary Laboratory and then as a poultry company veterinarian, he set up his own poultry veterinary practice in the southwest of England in 1985. He obtained his MSc in Applied Immunology in 1981, Certificate in Poultry Medicine and Production in 1989 and a Nuffield Farming Scholarship Trust to study the“Status of diseases specific to poultry and their control in Europe” in 1991.

He has been an Honorary External Lecturer at the University of Bristol Veterinary School on poultry medicine and production since 1999,a lecturer on the Institute of Animal Health’s poultry disease course since 2000 and is a regular monthly contributor of veterinary articles for backyard poultry keepers in the Practical Poultry magazine.