Hepatitis E virus strains infecting Swedish domestic pigs are unique for each pig farm and remain in the farm for at least 2 years

Abstract

Hepatitis E virus (HEV) genotype 3 (HEV3) is distributed globally and infects both humans and animals, mainly domestic pigs and wild boars, which are the major reservoirs. In this study, the prevalence of HEV among Swedish pigs was investigated by HEV RNA analysis in 363 faecal samples from 3‐month‐old piglets sampled twice (2013 and 2014) in 30 Swedish pig farms. Four different types of farms were investigated; organic, conventional closed (keeping the sow), satellites in a sow pool (conventional farms sharing sows) and conventional non‐closed farms (purchasing gilts). More than two‐thirds (77%) of the farms had HEV‐infected pigs. HEV RNA was found in faeces from 79 pigs (22%). Partial ORF1 could be sequenced in 46 strains. Phylogenetic analysis revealed a unique HEV3 strain for each farm. Strains sampled more than a year apart from the same farm were closely related, indicating that the same HEV strain is present for several years on the farm. Despite that only 4% of the Swedish pig farms were investigated, two farms had strains similar to those from humans, another had strains similar to wild boar HEV. The uniqueness of strains from each farm indicates a possibility to identify a source of infection down to farm level. This knowledge may be used by the farms to investigate the effectiveness of good hygiene routines to reduce the amount of HEV and thus the infection risk in the farm, and for Swedish public health authorities to identify cases of HEV transmissions from consumption of uncooked pork.

Long‐term surveillance for hepatitis E virus in an Italian two‐site farrow‐to‐finish swine farm

“…After depopulation of some rooms in the building housing HEV-positive growers, the virus was still detected afterwards. In previous studies (Kantala et al, 2015;Wang et al, 2019;Widen et al, 2011), the persistence of the same virus on farms was confirmed for up to 4 years but in our study this persistence lasted even longer (from 2012). The results of our study partially confirmed recent conclusions obtained by mathematical models designed to predict the length in time of HEV persistence on pig farms (Salines et al, 2020).…”

Infection dynamics and persistence of hepatitis E virus on pig farms – a review

“…The probability of an individual to become infected by a pathogen is dose dependent and related to route of exposure. For oral ingestion, Bouwknegt et al estimated the dose at which the probability of infection equals 50% at 1.4 * 10 6 HEV genomic copies (PI 50 ) [25]. Andraud et al reported similar results after orally inoculating twelve pigs with different doses, ranging from 10 4 to 10 8 HEV copies.…”

“…Phylogenetic analyses of HEV strains indicate on-farm persistence for two reasons. Firstly, farms often have a unique HEV strain, which can be seen in phylogenetic trees as a separate cluster for every farm [6,72,73]. Secondly, even multiple strains sampled from the same farms, with a long sampling interval, are often closely related [6,72].…”

“…Firstly, farms often have a unique HEV strain, which can be seen in phylogenetic trees as a separate cluster for every farm [6,72,73]. Secondly, even multiple strains sampled from the same farms, with a long sampling interval, are often closely related [6,72]. A French study did not find this close relationship between strains from a farm sampled twice, but multiple introductions on that farm could have occurred due to buying grower pigs from multiple origins [74].…”

“…Strains circulating in pigs and humans have a high sequence similarity, suggesting that transmission of HEV between pigs and humans is common [5,6]. Pig-tohuman transmission of HEV can occur via the consumption of inadequately cooked pork, and liver in particular [7].…”