Human adenovirus type 8 genome typing

Human adenovirus type 8 (HAdV-8) is a major causative agent of epidemic keratoconjunctivitis, which is frequently associated with community, industrial and nosocomial outbreaks. Restriction endonuclease (RE) analysis discriminates HAdV-8 isolates into genome types, making it possible to correlate between genomic variants, virulence and outbreak potential. RE analysis is performed using two sets of classification criteria, an Asian and a European system. So far, genome types HAdV-8A-8K and HAdV-8/D1-D12 have been included in the Asian and European classifications, respectively. Conventionally followed RE analysis has some inherent problems, such as the use of a neutralization test for HAdV-8 typing, which may misidentify some recombinant adenoviruses as HAdV-8 due to cross-reaction, the lack of a complete restriction profile for all genome types for purposes of comparison, and the absence of enzyme codes in the Asian classification system. In this review, we propose typing of HAdV-8 with phylogenetic analysis of the hexon and fibre genes prior to RE analysis due to the emergence of many recombinant types. Schematic restriction profiles for both classification systems were created by compiling all the published reports on genome types, and enzyme codes were included for the Asian classification system. The updated and simplified stepwise approach for HAdV-8 genome typing presented here could be useful for identifying either existing genome types or novel ones.