The transmission of ALV can occur vertically, from parent to offspring, with hens being able to pass the virus to their eggs. Infected chickens can shed the virus throughout their lives, and horizontal transmission can occur through the fecal-oral route. ALV is widespread in commercial chicken populations worldwide, although some breeding companies have initiated programs to eradicate it.
ALV infection can lead to the formation of tumors (lymphoid leukosis) in the liver, spleen, and bursa. Tumors can also occasionally be found in the kidneys and sex organs. The characteristics and frequency of tumors depend on the virus strain, chicken breed, age, and route of infection.
Clinical signs of ALV infection include:
- Loss of appetite
- Weakness
- Diarrhea
- Dehydration
- Weight loss
- Depression
- Enlarged bursa and sometimes an enlarged liver
- Infected birds may not necessarily develop tumors, but they may lay fewer eggs
