Cause

The disease is caused by an avian adenovirus (for exmple the Tipton strain) and is usually simultaneously accompanied by other immunosuppressive diseases such as infectious bursal disease or infectious anaemia. There are 12 known serotypes of avian adenoviruses that may be involved in the development of this disease.

Transmission

Egg transmission is an important factor. Horizontal transmission from bird to bird by contact with droppings. Once the bird becomes immuned, the virus can no longer be isolated from the droppings.

Species affected

Chickens, turkeys and pheasants and possibly other birds can be affected by avian adenovirus.

Clinical signs

Chickens with inclusion body hepatitis are affected at usually 5 to 7 weeks of age. The birds are listless, with ruffled feathers. Mortality is usually quite severe, up to 25% in the first 10 days of the disease.

Internal Lesions

Affected chickens have mottled livers, many with pinpoint necrotic and haemorrhagic spots. Pale bone marrow and in some cases in the presence of infectious anemia, gangrenous dermatitis can be seen. Kidneys are pale and swollen. The spleen is usually quite small (atrophy).
If Gumboro disease (infectious bursal disease) has been present in the birds, even if subclinical, the Bursa of Fabricius will be very small (atrophic). Such chickens are immune-suppressed and usually have more severe cases of inclusion body hepatitis and/or infectious anaemia.
Mature birds do not have clinical signs of adenovirus infection, they only show antibodies in their blood.

Diagnosis

Typical mottled livers with pinpoint lesions, pale bone marrow and kidneys, small spleen and bursa are good indications of the disease. In the case of HHS the typical lesion (hydropericardium) is also found. Histological examination (intranuclear inclusion bodies) of liver and/or virus isolation are helpful means of diagnosis.

Treatment and control

No treatment exists. Antibiotics can be used to prevent secondary bacterial infection and possible gangrenous dermatitis. The best method of control is to ensure adequate immunity against other immune suppressive diseases (e.g. infectious bursal disease). Chickens may be vaccinated during the first two weeks of life with an inactivated oil-emulsion vaccine.