Identification and preliminary characterisation of fowl adenoviruses from field cases

The first member of the family Adenoviridae was discovered by accident in 1953. Since then, its members have been isolated from virtually every class of vertebrates, which makes it an unusually large and diverse virus family. It was thought for a long time that the two first genera (Mast- and Aviadenovirus) were sufficient for proper classification. But as more genomes became available, more sophisticated diagnostic methods could be developed and could provide more detailed information. This lead to the acceptance of two new genera (Atand Siadenovirus) in 2002 and that of genus Ichtadenovirus in 2009. The Aviadenovirus genus underwent large changes with the acceptance of the new genera as two avian adenoviruses, egg drop syndrome virus and turkey haemorrhagic enteritis virus belong now to the new genera Atadenovirus and Siadenovirus, respectively. Fowl adenoviruses belong to genus Aviadenovirus and now consist of twelve serotypes divided into five species (Fowl adenovirus A to E). Most of them cause similar clinical and pathological signs and is diagnosed in the same disease. We typed the occurring adenoviruses in two chicken field cases with similar necropsy and same diagnosis (inclusion body hepatitis) using PCR systems targeting the viral DNA polymerase and the hexon gene. The amplified viruses proved to be aviadenoviruses, but from two different fowl adenovirus species. The type from one of the cases, as shown by the nucleic acid sequence of the PCR amplified partial hexon gene, resembled serotype 2 and 11 of species FAdV-D and the other virus resembled FAdV-8b of HAdV-E but were not equivalent with the prototypes. Similar results were obtained in studies in Canada where most of the cases were diagnosed with inclusion body hepatitis. One study with samples from two provinces found fowl adenovirus serotype 8 to be the dominating serotype in Ontario by 2002. The other study collected samples from 7 different provinces and found both serotype 8 and 11 causing almost the same number of cases, also showing that different regions may have FAdVs of different genetic composition. Our study may contribute to the studies on the identification of FAdV serotypes occurring in Hungary and causing different diseases