engleski

Hepatitis E virus (HEV): genetic relationship of the first identified human strain and swine strains in croatia

Hepatitis E is an important public health problem with a possibility of zoonotic transmission through contact with infected animals. The causative agent is an RNA virus belonging to the genus Hepevirus, family Hepeviridae. Four hepatitis E virus (HEV) genotypes have been recognized so far. Genotypes 1 and 2 are human specific and mostly isolated in areas where HEV is endemic, whereas genotypes 3 and 4 are isolated from humans as well as from other mammals. Identification and genetic typing of swine hepatitis E virus (HEV) strains, indicate their close relationship to human HEV strains and prove that swine could be recognised as reservoirs of HEV in nature. Therefore, the aim of our study was to investigate the potential genetic relationship of a human HEV strain identified for the first time in Croatia in a patient showing signs of acute hepatitis, with strains detected in swine from the same geographical area (within the distance of 100 kilometers from the patients habitat). For better epidemiological understanding, samples originating from swine (blood, spleen and liver) were collected from different age categories and breeding systems (two large commercial farms and small farms up to 20 animals). All together, 140 domestic pigs from large farms and 12 pigs from small breeding farms have been included in this study. All samples were tested by a nested RT-PCR protocol in order to amplify a fragment within the metil-transferase gene of 287 base pairs (bp). Representative positive samples, including the human HEV strain were sequenced and phylogenetically analysed using the Neighbor-Joining method and the Kimura-2 Parameter model. HEV RNA was detected in swine samples showing a high viral prevalence (31.5%), regardless of the breeding system or age category. All analysed RNA sequences (the human and swine HEV strains) clustered into phylogenetic group 3, proving their close genetic relationship. HEV RNA sequences originating from swine further clustered into subgroup 3a and 3e, indicating a possible transmission of HEV among different breeding systems and age categories of swine. However, the human HEV strain clustered into subgroup 3f showing the highest similarity (95.5%) with a reference swine strain identified in The Netherlands. Our results support the fact that swine in Croatia are reservoires of HEV, even though their true role in the chain of viral spread should still be identified. The analysed human HEV strain could not be directly connected to swine from local breeding farms included in this study. Therefore, the source of the first reported human infection in Croatia still remains unidentified. We conclude that further epidemiological data is needed, based on a larger amount of tested samples, including different animal species and swine products. This would allow us to estimate the public health risks and identify possible transmission routes and dynamics of infection.

Hepatitis E virus; human and swine strains; phylogenetic relationship; Croatia

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