Abstract
Fowl adenovirus (FAdV) is a double-stranded DNA virus with a non-enveloped structure comprising three major proteins known as hexon, penton, and fiber. Molecular analysis which emphasis on hexon and fiber proteins is currently the major focus of curiosity for FAdV antigenicity and pathogenicity. Recently, disease outbreaks associated with FAdV infection such as inclusion body hepatitis (IBH), hepatitis-hydropericardium syndrome (HHS), and gizzard erosion were commonly reported and continue to increase worldwide. Studies on the virulence gene of the virus were intensively conducted to provide a better understanding on the role of these major capsid proteins in the development of a safe and effective vaccine against the disease in the poultry industry. This paper highlighted on variation of the fiber and hexon genes, their importance in genotypes and serotypes differentiation and infectivity between FAdV strains. It appears that the L1 loop of hexon and the knob of fiber genes are the infectivity markers for FAdV infection. The fiber-2 protein plays a major role in FAdV pathogenicity than the hexon protein, whilst the fiber-1 protein is important for viral replication and assembly regardless of virulence capability instead of infectivity. The hexon protein plays a major role in virus infectivity and tissue tropism. These findings could further enhance on the knowledge of FAdV strains classification and evolution, diagnosis, and strategies to prevent and control FAdV infection and outbreaks in chicken farms.

Key words: Fowl adenovirus (FAdV); infectivity; hexon; fiber; antigenicity; pathogenicity