Lymphoid leukosis In Poultry

Lymphoid leukosis is a tumour-producing viral disease of chickens. Lymphoid leukosis is characterized by marked enlargement of the liver. The disease occurs any time after 16 weeks of age. The incidence is highest at about sexual maturity. Lymphoid leukosis is usually a problem of laying hens. Lymphoid leukosis and Marek's disease closely resemble each other in their involvement of liver and other organs. Whereas, today, Marek's disease is a burning problem of the poultry industry, lymphoid leukosis has been largely controlled through breeding and is now uncommon.

Cause

Alpharetroviruses, cause of lymphoid leukosis, are widely prevalent in commercial chickens. Infection occurs in all chicken flocks. By sexual maturity, most birds are exposed. However, the incidence of clinical disease is usually low.

Spread

Lymphoid leukosis virus is transmitted both vertically from hen to progeny through the egg, and also horizontally from bird to bird by direct or indirect contact. Usually only a small number of chicks are infected vertically, and the majority become infected by contact with vertically infected chicks during rearing.

Symptoms

I. The symptoms are non-specific.

2. The birds are usually pale and emaciated, and show loss of appetite.

3. The comb may be pale, shrivelled, and of bluish discoloration (cyanotic).

4. Diarrhoea may occur and wattles may be pale.

5. The abdomen is usually very large because of the massive liver.

Postmortem Findings

I. The liver is greatly enlarged .

2. The spleen, bursa of Fabricius, kidneys, and ovary are also usually enlarged.

Diagnosis

Postmortem findings may suggest lymphoid leukosis. However, as lymphoid leukosis closely resembles Marek's disease, both diseases can be differentiated with difficulty. Diagnosis is possible in most cases on careful microscopic examination. However, when distinct lymphoid tumours are present in the bursa, a diagnosis of lymphoid leukosis can be made. Such tumours in bursa are absent in Marek's disease.

Treatment

No treatment or vaccines are available.

Control

I. Control must be based on high standards of hygiene and flock management to reduce infection from the environment.

2. As the infection is egg transmitted, it cannot be prevented by rearing chicks in isolation.