Big liver disease in Birds

Big liver disease is a synonym to Avian Lymphoid Leucosis which is also known as Visceral leucosis. Avian leucosis is a group of diseases of chicken comprises of lymphoid, erythroid, myeloid leucosis, Other tumours such as fibroma, haemangioma, nephroblastoma and Osteopetrosis. Avian leucosis is prevalent throughout the world. Lymphoid leucosis (LL) is the commonest neoplastic condition in chicken caused by avian leucosis virus (ALV) usually occurs between 14th to 30th week of age. Incidence is highest at about sexual maturity (Vegad and Katiyar, 2001) which induces lymphoma in chicken called Lymphoid leucosis (LL) (Pizer and Humpheries, 1989). Avian neoplastic diseases are responsible for economic loss due to both mortality and depressed performance (Panda, 1983). Transmission of ALV occurs both horizontally and vertically (Payne and Venugopal, 2000). It is a lymphocytic lymphoma arising from malignant lymphocytes of bursal origin and later the malignant lymphocytes migrate and proliferate in other visceral organs to form tumors (Purchase and Burmester, 1972). ALV are classified into five subgroups (A, B, C, D and J) based on their host range, viral envelope interference and cross-neutralization patterns. ALV subgroups A and B are more commonly associated with lymphoid leucosis (Payne and Fadly, 2003). It is called big liver disease, because the liver is usually enlarged with nodular tumours. Commonly found in broiler breeders around 1994-1999. Nowadays, hardly seen due to severe eradication programs on pedigree level of the top commercial breeds in the world. Local breeds may still harbor the viruses.