Occurrence: Worldwide.   Species affected: Chickens.   Age affected: 8-12 weeks of age.

Causes: RNA retrovirus- belongs to subgroup B of lymphoid leukosis viruses.

Effects: Incubation period is 1 month. Long bones of legs show a uniform or irregular thickening of the diaphysial or metaphysial regions. A stunted pale bird with "boot-like" shanks, walking with a stilted gait or limp is characteristic of the disease.

This is a rare type of leucosis. Chickens of 8-12 weeks are susceptible to this chronic disease. The agent involved in the aetiology is a RNA virus belonging to the family retroviridae, which belongs to subgroup B of lymphoid leucosis viruses.

It is spread transovarian or laterally among hatchmates.

The incubation period is 1 month.

Long bones of the limbs show a uniform or irregular thickening of the diaphysial or metaphysical regions.

A characteristic sign is a stunted, pale bird, with "boot-like" shanks. The birds walk with a stilted gait or limp.

Bone alternations occur in the diaphysis of the pelvis, shoulder girdle and ribs. Distinct pale yellow foci occur against the grey-white translucent normal bone. The periosteum is thickened and abnormal bone is spongy and is easily cut.

Osteopetrosis and lymphoid leucosis frequently occur together in the same bird.

There can be atrophy of the spleen, bursa and thymus.

Gross and microscopic observation of bone tumours are diagnostic. Spongy bone converges centripetally toward the centre of the shaft. There is an increase in size and irregularity of Haversian canals and increase in number and size of lacunae. Osteocytes are more numerous, large and eosinophilic. New bone is basophilic and fibrous.

It simulates rickets and osteoporosis.

Virus-free breeders should be selected

None.

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