Full genome analysis of Philippine indigenous subgenotype IA hepatitis A virus strains from Japanese patients with imported acute hepatitis A

Aim Hepatitis A virus (HAV) is the most common cause of infectious hepatitis worldwide. Although hepatitis A cases imported from South-East Asian countries, including the Philippines, have been reported in Japan, the molecular epidemiological data have been limited for these HAV-endemic countries. Methods The full-length genomic sequences of HAV isolates were determined and subjected to the phylogenetic analyses. Results The HAV isolates (HA12-0796 and HA12-0938) obtained from two Japanese patients who developed acute hepatitis A in July 2012, 1 month after traveling to the Philippines, where they consumed undercooked shellfish, differed by only one nucleotide (nt) over the entire genome. These HAV isolates of genotype IA were 99.1-99.5% identical within 228-237 nt to those recovered from river water in the Philippines, suggesting that the HA12-0796 and HA12-0938 isolates represent HAV circulating in the Philippines. HAV isolates belonging to one of the two IA sublineages (IA-2) which were implicated in some of the mini-epidemics in 2010 in Japan are hypothesized to be connected with the Philippines. In support of this speculation, the present IA isolates (HA12-0796 and HA12-0938) shared 98.8% identity over the entire genome with one IA-2 isolate (HAJIH-Fukuo10) recovered from a Japanese female who developed a domestic HAV infection during the mini-epidemics. In the phylogenetic tree constructed based on the entire genome, these three isolates (HA12-0796, HA12-0938 and HAJIH-Fukuo10) segregated into a cluster with a bootstrap value of 100%. Conclusion These results indicate that HAV isolates belonging to the IA-2 lineage might have been imported from the Philippines.