Inclusion body hepatitis (IBH) is an acute liver disease of young broiler chickens caused by the fowl adenovirus (FAdV). The disease was first described in domestic chickens in 1963, and is characterized by sudden onset, increased mortality and hepatitis accompanied with intranuclear inclusion bodies.
IBH is mainly seen in commercial broiler chickens, however it has also been described in pigeons, American kestrels, geese, parrots, and merlin. IBH occurs in several geographical regions in Southeast Asia, Europe, Middle East, Europe, Australia, New Zealand, North America, Mexico, Central and South America.
Affected flocks are often co-infected with other immunosuppressive viruses such as infectious bursal disease virus
or chicken infectious anemia virus
which predispose birds to developing IBH.
IBH is characterized by a sudden onset of increased mortality of 1-10%, with a short clinical course of 4-5 days. The most common symptoms described in affected birds with this disease include mild, yellowish diarrhea, lethargy, and decreased appetite.
Fowl adenoviruses can be transmitted to chickens both vertically and horizontally. The virus enters via the alimentary tract (and, in some cases, by the conjunctiva and nasal passages) and primary replication occurs in the nasopharynx and intestine. There is frequently a viremic stage in the infection with widespread dissemination of virus to secondary sites of replication. Infections can often be latent, and reactivated with stress.
Diagnosis of IBH is based on virus isolation (from the liver) and characteristic necropsy lesions, which include a pale, friable, swollen liver with focal to extensive necrosis, and large basophilic large basophilic intranuclear inclusion bodies associated with adenovirus-like particles in hepatocytes, situated in the periphery of necrotic foci.