Avian leukosis virus

Avian leukosis virus (ALV) infects mainly chickens but can also infect pheasants, partridges and quail.

The virus is not highly contagious and is readily inactivated by disinfectants. ALV 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 worldwide in commercial chickens, although some breeding companies have implemented erradication schemes.


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.

Clinical signs

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.

Clinical signs:

  • Loss of appetite
  • Weakness
  • Diarrhoea
  • Dehydration
  • Weight loss
  • Depression
  • Enlarged bursa and sometimes an enlarged liver
  • Infected birds may not necessarily develop tumours, but they may lay fewer eggs

Pirbright's research on avian leukosis virus

Economic losses stemming from decreased productivity and mortality in ALV-infected poultry are a global concern, estimated to reach millions of pounds annually. 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. Additionally, ongoing investigations are aimed at understanding the mechanisms by which the virus interacts with its host to induce tumorigenesis.

Research papers

Pang Y, Zhou D, Xue J, Zhou J, Zhang Y, Zheng G, Yuan S, Yao Y, Cheng Z (2019)

Virus Research 264 , 32-39
Zhu M, Zhou J, Ma X, Li G, He S, Tang H, Yao Y, Cheng Z (2019)

Research in Veterinary Science 123 , 65-70
Qian K, Tian X, Shao H, Ye J, Yao Y, Nair V, Qin A (2018)

BMC Veterinary Research 14 (1) , 295
Zhou D, Xue J, He S, Du X, Zhou J, Li C, Huang L, Nair V, Yao Y, Cheng Z (2018)

Retrovirology 15 (1) , 45


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