The first avian adenovirus (AAV) associated with clinical disease was isolated from an outbreak of respiratory disease in quail in 1950 (Olson, 1950). Since that time, AAVs have been found in all types and breeds of chickens and from a variety of other avian species. The infections may be asymptomatic or associated with several clinical and pathological conditions. Vertical transmission via the egg is the most common way of transmission. Also horizontal transmission through faeces, contaminated egg trays, crates and trucks plays a role in the infection route. Studies have demonstrated the presence of antibodies in healthy poultry, and viruses have been isolated from normal birds. Avian adenoviruses in chickens are the etiologic agents of 2 diseases known as inclusion body hepatitis (IBH) and hydropericardium syndrome (HP). In some cases each condition is observed separately, however, recently the 2 conditions have frequently been observed as a single entity; therefore, the name hepatitis hydropericardium has been widely used to describe the pathologic condition. The syndrome is an acute disease of young chickens associated with anemia, haemorrhagic disorders, hydropericardium and high mortality.

Key words: Avian Adenoviruses infections; Egg drop syndrome; Hydropericardium syndrome; Inclusion body hepatitis