Genetic characterisation of adenovirus type 8 isolated in Hiroshima city over a 15 year period

Aims: To investigate the genetic differences among the strains of adenovirus type 8 (Ad8) circulating in Hiroshima city, Japan, and to study their circulation pattern. Methods: One hundred and twenty nine strains of adenovirus type 8 (Ad8) were isolated in Hiroshima City over a 15 year period (1983-97) from patients with keratoconjunctivitis, and analysed with six restriction enzymes-BamHI, HindIII, PstI, SacI, SalI, and Smal-to investigate possible relations among the isolates and their genetic variability. Seven hypervariable regions of the hexon gene that carry the type specific epitope were also sequenced to investigate the variation among the genome types. Results: Restriction endonuclease analyses yielded three known genome types (Ad8A, 13 samples; Ad8B, seven samples; and Ad8E, 35 samples) and a novel genome type (Ad81, 74 samples). Ad8A, Ad8B, and Ad8E were closely related, with 96% homology, whereas Ad81 had only 71% homology. Ad8A, Ad8B, and Ad8E shared 91.8% and 96.4% homology with regard to their amino acid and nucleotide sequences, respectively, with the isolate 1127 (accession no X74663). However, when compared with AAA, Ad8B, Ad8E, and isolate 1127, Ad81 shared only 62.7% and 69.9% homology with regard to amino acid and nucleotide sequences, respectively. Ad8A, Ad8B,and Ad8E had a unique 31 amino acid deletion in the hypervariable region I of the hexon gene, whereas Ad81 had a 33 residue deletion. The Ad8E strain that circulated from 1984 to 1995 was stable among the study population. Ad81 was isolated from an outbreak of epidemic keratoconjunctivitis in 1995 and was also isolated from sporadic cases until 1997. Conclusions: These results confirmed that genetic variability occurs in Ad8 in the microenvironment and revealed the emergence of a new genome type (Ad81).