AVIAN LEUCOSIS
- 1. AVIAN LEUCOSIS SURYAADHIKARI B V Sc & AH, PU
- 2. INTRODUCTION • Synonym- Lymphoid leucosis , Big liver disease • Avian lymphoid leucosis is the a neoplastic disease of chickens cause by a virus of the leucosis / sarcoma group and characterized by tumor formation of the bursa of fabricius with metastasis to other tissues and all abdominal organs and the neoplastic changes start in bursa and metastasize to the organs, particularly the liver, spleen and kidneys. • Lymphoid leucosis is a B cell tumor which start in the bursa and before sexual maturity, may spread to `other organs Mature birds are more affected than young birds. • Until recently, lymphoid leukosis has been the commonest form of leukosis.
- 3. ETIOLOGY • Avian leukosis is caused by certain members of the leukosis/sarcoma group of avian retroviruses. • These viruses are commonly called avian leukosis viruses and belong to subgroups A, B, C, D, E, and J. • All field strains of avian leukosis virus are oncogenic, although some differences in oncogenicity and replicative ability have been recognized.
- 4. TRANSMISSION • Both horizontal and vertical • Cocks may act only as virus carriers and sources of contact or venereal infection to other birds. • Transmission can be reduced or eliminated by strict sanitation.
- 5. Vertical & Horizontal Transmission
- 6. SUSCEPTIBLE HOSTS Chickens, some exotic birds.
- 7. CLINICAL FINDINGS • Depression. • Loss of weight. • Persistent low mortality. • Enlargement of abdomen, liver or bursa. • Many are asymptomatic. • Chickens with lymphoid leukosis show nonspecific clinical signs including inappetence, weakness, diarrhea, dehydration, and emaciation. • The disease occurs in 14 – 30 weeks old birds.
- 8. PM LESIONS • Focal or diffuse white or gray neoplastic lesions are seen in the bursa, liver, spleen and kidneys. • External tumours may be seen, and the abdomen is enlarged and feathers are sometimes spotted with urates and bile. • Tumours may be nodular, miliary or diffuse. • Bursa are always enlarged and may contain nodular tumours. • Tumors are smooth, soft and glistening. • Ecchymotic haemorrhages around the skin follicles of the wing
- 9. Diffuse nodular lesions in the liver, spleen, intestine and heart.
- 10. Neoplastically transformed ovary in Lymphoid leucosis
- 11. Diffuse and focal tumor lesions in the heart
- 12. Focal neoplastic lesions in kidneys.
- 13. The internal organs of a chicken affected by lymphoid leukosis
- 14. DIAGNOSIS • Post mortem lesions and tumors are diagnostic. • Tumors occur in birds >14 wk old. • In lymphoid leukosis, the lymphoid cells are histologically uniform in character, large, and contain IgM and B-cell markers on their surface. • Tumors can be differentiated from those of Marek’s disease by gross and microscopic pathology and by molecular techniques. • ELISA kits for detection of antibodies to avian leukosis virus subgroups A, B, and J are available commercially.
- 15. DIFFERENTIAL DIAGNOSIS • Marek’s disease • Coligranuloma
- 16. DIFFERENT BETWEEN MAREKS & LYMPHOID LEUCOSIS
- 17. TREATMENT • No treatment or vaccines are available. • Supportive care.
- 18. PREVENTION • Eradication of the infected hens- best methods of controlling it. • Lymphoid leukosis appears to be controlled best by reduction and eventual eradication of the causative virus. • Breeder flocks are evaluated for viral shedding by testing for viral antigens in the albumen of eggs with enzyme immunoassays or by biologic assays for infectious virus. • Eggs from shedder hens are discarded, so that progeny flocks typically have reduced levels of infection. If raised in small groups, infection-free flocks can be derived with relative ease. • These control measures are applied only to primary breeder flocks. • Voluntary programs to reduce viral infection have already reduced mortality from lymphoid leukosis and improved egg production in most layer strains; similar programs are underway in certain meat strains.
- 19. • Some chickens have specific genetic resistance to infection with certain subgroups of virus. • Although genetic cellular resistance will unlikely replace the need for reduction or eradication of the virus, the cellular receptor gene has been cloned, and quick molecular assays for viral susceptibility could be developed. • Thus far, vaccination for tumor prevention has not been promising. • However, recombinant vaccines lacking infectious avian leukosis virus can induce antibodies in breeders to ensure protective maternal antibodies in progeny chicks and may be an attractive adjunct to eradication programs.