Avian leucosis complex is a highly contagious disease of poultry and other avian species characterised by occurrence of neoplasm in haemopoeitic system. In many cases the lesion can be observed in other sites also. Lymphoid leucosis is the most common.
Mainly two types of viruses a. Avian leucosis complex virus (ALC) and b. Rous Sarcoma virus (RSV). They possess many properties in common. Virus is RNA virus and they are susceptible to 0.5% phenol and 0.5% formalin. Most of the viruses were not destroyed by UV light. Heating at 56˚C for 30 minutes will destroy the virus. Natural host is chicken. Turkeys, pigeon, quails, ducks and water fowl are also affected. Viruses can grow in chicken embryo fibroblast. Also possible to grow in embryonated eggs (11 day old).
Transmission:
Virus can be transmitted vertically from parent to offspring or horizontally from bird to bird. Transmission through egg is also possible. Congenitally infected birds shed large amount of virus in their droppings and saliva.
Different ALC forms are1. Big liver disease or Lymphoid leucosis: In addition to liver, other organs like spleen and kidney will be affected. Liver will be enlarged and this can be palpated and distension of abdomen can be seen. In cadence is more in bird above 5 months of age. Symptoms are weight loss, emaciation, low egg production, diarrhoea. It is proved that, surgical/hormonal removal of Bursa of Fabricious reduces the incidence.
Feature
Marek’s disease
Lymphoid leucosis
Age
6 weeks or older
16 weeks or older
Symptoms
Frequently paralysis
Non-specific
Macroscopic Lesions
-Neural enlargement
-Frequent
-Absent
-Bursa of Fabricius
-Diffuse enlargement or atrophy
-Nodular tumors
-Tumors in skin, muscle, proventriculus
-May be present
-Usually absent
Microscopic lesions
–Neural involvement
-Yes
-No
-Liver tumors
-Diffuse
-Often focal
-Spleen
-Either atrophy of follicles or interfollicular tumor
-Intrafollicular tumors
-Bursa of Fabricius, CNS
-Yes
-No
-Lymphoid proliferation of skin and feather follicles
-Yes
-No
Cytology of tumors
Pleomorphic lymphoid cells including lymphoblasts, small, medium and large lymphocytes and reticulum cells. Rarely may only be lymphoblasts
Lymphoblasts
Category of neoplastic lymphoid cell
T cell
B cell
2. Erythroblastosis: Precursors of RBCs will be in large numbers. Two types. A. Proliferative form and b. Anaemic form. In both cases comb and wattle will be pail or yellowish white or cyanotic. But in proliferative form large numbers of precursors can be seen in viscera. As a result, bone marrow and spleen seen as intense cherry red or Mahogany black colour. Number of RBC seen is less in anaemic form. Liver may show enlargement, round but colour will be pale.
3. Myeloblastosis: Number of granulocyte will be more. Cytoplasm will be basophilic and nucleus in centre position. Massive accumulation of myeloblasts can be seen both intravascularly and extravascularly.
4. Osteopetrosis: Long bones of the limbs will be affected. There will be regular or irregular thickening of long bones. Such type of thickening cause boot like appearance of long bones and bone marrow appears jelly like or sponge like.
5. Myelocytomatosis: Blast cells and nucleus will be eccentric. Cytoplasm show acidophilic granules. Proliferated cells seen along with bones of the body like sternum and skull. Bones will be very thin and easily broken.
Rous sarcoma Virus Infection: cause pock lesions when inoculated to 11 day old chicken embryo on CAM. Many RSV require the presence of ALC, so that they can multiply. Such ALC viruses are known as helper viruses. Similarly, many ALC virus cause inhibition of RSV, and such viruses are called as resistance inducing factors.
Diagnosis:
History, clinical signs, histopathological lesionsand serological tests. Virus can be isolated from plasma, serum or tumour tissues. Complement Fixation Test for detecting ALC is COFAL.
Prevention:
No vaccine available. Selective breeding can be done.
