Characteristically, lymphoid leukosis is a disease of adult chickens; however, the disease appears to be increasing in importance for turkeys and game birds. Although the virus of lymphoid leukosis can produce various responses (blood, bone, lymph), the lymphoid tumor response is the most common.
The disease is transmitted in a variety of ways. The causative viral agent is passed out of the body of infected birds via eggs and feces. The virus may be transmitted mechanically from infected birds to susceptibles by blood-sucking parasites or by man in such procedures as fowl pox vaccination.
Lymphoid leukosis characteristically produces lymphoid tumors, particularly in the liver and spleen. The tumors may also affect other visceral organs such as ovary and lungs. Affected birds may die without preliminary symptoms, but the disease usually is chronic in nature and affected birds show loss of appetite, progressive emaciation and diarrhea. Clinically affected birds invariably die. Losses due to the disease are most severe shortly after onset of egg production, but losses will continue for as long as the flock is retained. Total loss may approach twenty percent during the life of a flock.
Clinical diagnosis of lymphoid leukosis is based upon flock history and disease manifestations. The lymphoid disease cannot be readily distinguished from the visceral response to Marek’s disease; however, there are some features that aid in differential diagnosis.
There is no treatment for lymphoid leukosis. Although the disease cannot be prevented completely, there are certain steps that can be taken to help control the level of infection within a flock. Some steps are:
Buy resistant strains of birds since genetic resistance is a deterrent,
Brood in isolation and do not mix birds of different ages, especially through six weeks of age,
Keep the incubator clean and disinfected,
Control blood-sucking parasites,
Good care, limiting stress, and adequate ration will be of benefit.