A Review on inclusion body hepatitis (IBH): An emerging problem in Sri Lanka

Viruses belong to the Family Adenoviridae can infect a wide range of vertebrates. These viruses are classified into different genera based on phylogenetic distance, genome organization, and host range. From those genera, Aviadenovirus only infect birds and are serologically different from other adenovirus genera. Fowl Adenoviruses (FAdVs) fall under the Aviadenovirus genus and have a considerably large genome. The FAdV genome comprises non-segmented, linear double-stranded DNA (dsDNA) of 43-46 kbp. The capsid of FAdVs is composed of hexons, penton bases, and fiber proteins, which are vital for cellular interaction and immune responses. Inclusion Body Hepatitis (IBH) is a significant disease caused by FAdVs, impacting broiler chickens primarily. Inclusion Body Hepatitis results in sudden mortality, poor growth, and other clinical signs, contributing to economic losses in the poultry industry, and is transmitted  horizontally through contaminated excretions and vertically via embryonated eggs from infected parent flocks. The disease pathogenesis involves replication in the alimentary and respiratory tract epithelium, leading to viremia and dissemination to organs. Gross pathological findings mainly include swollen liver with necrotic foci and multifocal petechial hemorrhages. Histopathologically, degeneration, necrosis, and the presence of intranuclear/intracytoplasmic, basophilic/eosinophilic inclusion bodies are observed mainly in hepatocytes. Diagnosis of IBH involves detecting intranuclear inclusion bodies in hepatocytes, virus isolation, and molecular techniques like PCR for serotyping. Control strategies include strict biosecurity measures, continuous disease surveillance, breeder monitoring, and vaccination. Inactivated and live vaccines are commonly used, with autogenous inactivated vaccines prepared from prevalent serotypes for prevention in endemic regions. Since 2021, IBH outbreaks have been reported in Sri Lanka. The objective of this review is to provide a quick overview of the members and viral structure of the Family Adenoviridae as well as an in-depth review of IBH, one of the main diseases caused by FAdV in poultry.