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New findings regarding the epidemic history and population dynamics of Japan-indigenous genotype 3 hepatitis E virus inferred by molecular evolution

Authors


  • The GenBank/EMBL/DDBJ accession numbers of the new HEV sequences in this study are AB578953-AB578957, AB578959-578963 and AB581581- AB581598.

Correspondence

Tatsunori Nakano, Department of Internal Medicine, Fujita Health University Nanakuri Sanatorium, Otoricho 424-1, Tsu, Mie 514-1295, Japan

Tel: +81-59-252-1555

Fax: +81-59-252-1383

e-mail: tanakano@sf.starcat.ne.jp

Abstract

Background

Since previous studies have investigated the population dynamics of Japan-indigenous genotype 3 hepatitis E virus (HEV) using virus sequences, more nucleotide sequences have been determined, and new techniques have been developed for such analysis.

Aims

To prevent future hepatitis E epidemic in Japan, this study aimed to elucidate the cause of past HEV expansion.

Methods

The epidemic history of Japan-indigenous genotype 3 HEV was determined using the coalescent analysis framework. Bayesian skyline plot (BSP) and Bayesian estimate of phylogeny with relaxed molecular clock models were calculated using Markov chain Monte Carlo sampling.

Results

Japan-indigenous strains consist of New World strains (subtype 3a), Japanese strains (3b) and European strains (3e). The oldest lineage, 3b, appeared around 1929. Lineages 3a and 3e appeared around 1960. BSPs indicated similar radical population growth of the 3a and 3b lineages from 1960 to 1980.

Conclusions

Population dynamics of the three lineages shared some common characteristics, but had distinguishing features. The appearance of 3a and 3e lineages coincides with the increase of large-race pig importation from Europe and the USA after 1960. The epidemic phase of 3a and 3b strains from 1960 to 1980 could be related to increased opportunity for HEV infection arising from large-scale pig breeding since 1960. Our observations revealed new findings concerning the close relationship between the epidemic history of Japan-indigenous genotype 3 HEV and the improvement of the Japanese pig industry. Infection control in pig farms should be an effective method of preventing HEV infection in humans.

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