Lymphoid Leukosis in Poultry: Causes, Symptoms & Prevention

Lymphoid leukosis is a type of cancer in poultry caused by the avian leukosis virus. It is a neoplastic condition characterized by the development of tumors in the internal organs of chickens and turkeys. While there are various forms of this disease, the most common one is Lymphoid leukosis, whereas other forms are rare.

Causes of Lymphoid Leukosis

Lymphoid leukosis is caused by an RNA virus known as the avian leukosis or sarcoma group. It primarily affects adult chickens over 6 months of age and is the most common disease caused by the leucosis/sarcoma group of viruses.

Transmission of the Disease

The disease is primarily transmitted vertically, directly from the infected parent to the offspring. The most common route of transmission is from infected hens to their progeny through the eggs, with approximately 1 in 20 eggs being infected. Chicks that acquire the infection through the egg are immune-intolerant and have a higher risk of developing tumors. Horizontal transmission among young birds is also possible.

Clinical Signs of the Disease

Clinical signs of lymphoid leukosis are typically not seen before the age of 4 months. The main feature of lymphoid leukosis is the presence of visceral tumors. The disease is more common in birds older than 25 weeks and is characterized by decreased egg production, osteopetrosis (enlarged bones) in the legs and wings, bowed and thickened legs, pale and emaciated appearance, dehydration, loss of appetite, shriveled comb, occasional cyanosis, enlarged abdomen, and, rarely, blood leukosis. Infected chickens also exhibit depression before succumbing to the disease.

Post-mortem Lesions

Post-mortem examination reveals organ enlargement, particularly in the liver and spleen, due to the presence of tumors. Tumors may also develop in the kidney, lungs, ovaries, testicles, and bone marrow. The size of the tumors can vary, and they are typically soft in consistency.

Diagnosis

Diagnosis of lymphoid leukosis is based on clinical signs such as cachexia (generalized wasting), the presence of tumors, and the age of the birds (4 months and above). Confirmation can be made through histopathological examination.

Differential Diagnosis

Marek's disease, which can cause paralysis, should be considered as a differential diagnosis. However, it typically affects younger birds.

Control of the Disease

The culling of affected birds is recommended to prevent the spread of the disease. The most effective preventive measure is to identify and eliminate infected breeders through laboratory detection. Breeding from leucosis-free offspring can help in eradicating the disease. Obtaining day-old chicks from leucosis-free breeders can also contribute to disease eradication.

Treatment of the Disease

No specific treatment is available for lymphoid leukosis. The best approach is to control the disease through the reduction and eventual eradication of the causative virus from the breeding flocks.