Avian leukosis virus (ALV) infects mainly chickens but can also infect pheasants, partridges and quail. It belongs to the Alpharetrovirus genus of the family Retroviridae. It is divided into subgroups A, B, C, D, E and J, depending on their viral envelope proteins which determine immune response and host range. The ALV envelope encases a capsid and a single stranded RNA genome.
Infection with ALV can cause tumour formation (lymphoid leukosis) in the liver, spleen, bursa and are found occasionally in the kidneys and sex organs. The nature of the tumours and their frequency depend on virus strain, chicken breed, age, and route of infection.
- Loss of appetite
- Weight loss
- Enlarged bursa and sometimes an enlarged liver
- Infected birds may not necessarily develop tumours, but they may lay fewer eggs
The virus is not highly contagious and is readily inactivated by disinfectants. The virus can be vertically transmitted (passed directly from parent to offspring). Hens are able to shed the virus or viral components into eggs. Chickens infected at hatching shed virus their entire lives. Horizontal transmission (spread from bird to bird) can also occur by the faecal-oral route.
ALV is present world wide in commercial chickens, although some breeding companies have put erradication schemes in place.
Impact for Society – what are we doing?
Economic losses due to reduced productivity and ALV mortality are world-wide, and estimated to be millions of pounds each year. Research at the Institute is focussed on discovering what drives the viral infection and how the genetic makeup of chickens alters how susceptible they are. Research into determining how the virus interacts with the host to create tumours is also ongoing.