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

Hepatitis E Virus RNA Detection in Liver and Muscle Tissues Sampled from Home Slaughtered Domestic Pigs in Central Italy

Hepatitis E virus is a worldwide emerging foodborne pathogen; raw or undercooked meats and liver pork products can cause infection through the orofecal route. In Central-Southern Italy, small traditional farming method, associated with the possibility of environmental sharing with wild species, can facilitate HEV diffusion and persistence. The aim of this study was to determine HEV genotype and subtype in Marche region from home slaughtered domestic pigs involved in small and traditional food chains. A total of 236 liver and muscle tissues and 6 pooled salami samples were screened. Laboratory workflow started with homogenization, followed by RNA extraction. Nested reverse transcription PCR and qRT-PCR were used to amplify specific parts of overlapping open reading frames belonging to the HEV genome. A total of 42/236 (17.79%) liver and 8/236 (3.39%) diaphragm specimens were positive; none of the pooled salami specimens showed positive HEV signal. The discovered HEV3c presented high nucleotide similarities with ones amplified from wild boar populations hunted in the same province. Extensive farming methods and environmental sharing with wild animal species support cross-infection infections, as observed in the present study. Although salami resulted negative for HEV RNA detection, the effects of food technologies on viral loads remain unclear. Therefore, further scientific investigations coupled with efficacious standardized laboratory procedures will be the next challenge.

Biosecurity measures to control hepatitis E virus on European pig farms

Hepatitis E virus (HEV) genotype 3 is a prevalent zoonotic pathogen in European pig farms, posing a significant public health risk primarily through the foodborne route. The study aimed to identify effective biosecurity measures for controlling HEV transmission on pig farms, addressing a critical gap in current knowledge. Utilizing a cross-sectional design, fecal samples from gilts, dry sows, and fatteners were collected on 231 pig farms of all farm types across nine European countries. Real-time RT-PCR was employed to test these samples for HEV. Simultaneously, a comprehensive biosecurity questionnaire captured data on various potential measures to control HEV. The dependent variable was HEV risk, categorized as lower or higher based on the percentage of positive pooled fecal samples on each farm (25% cut-off). The data were analyzed using generalized linear models (one for finisher samples and one for all samples) with a logit link function with country and farm type as a priori fixed factors. The results of the final multivariable models identified key biosecurity measures associated with lower HEV risk, which were the use of a hygienogram in the breeding (OR: 0.06, p = 0.001) and/or fattening area after cleaning (OR: 0.21, p = 0.019), the presence of a quarantine area (OR: 0.29, p = 0.025), testing and/or treating purchased feed against Salmonella (OR: 0.35, p = 0.021), the presence of other livestock species on the farm, and having five or fewer persons in charge of the pigs. Contrary to expectations, some biosecurity measures were associated with higher HEV risk, e.g., downtime of 3 days or longer after cleaning in the fattening area (OR: 3.49, p = 0.005) or mandatory handwashing for farm personnel when changing barn sections (OR: 3.4, p = 0.026). This novel study unveils critical insights into biosecurity measures effective in controlling HEV on European pig farms. The identification of both protective and risk-associated measures contributes to improving strategies for managing HEV and underscores the complexity of biosecurity in pig farming.

Hepatitis A Virus and Hepatitis E Virus as Food- and Waterborne Pathogens-Transmission Routes and Methods for Detection in Food

Foodborne viruses are an important threat to food safety and public health. Globally, there are approximately 5 million cases of acute viral hepatitis due to hepatitis A virus (HAV) and hepatitis E virus (HEV) every year. HAV is responsible for numerous food-related viral outbreaks worldwide, while HEV is an emerging pathogen with a global health burden. The reported HEV cases in Europe have increased tenfold in the last 20 years due to its zoonotic transmission through the consumption of infected meat or meat products. HEV is considered the most common cause of acute viral hepatitis worldwide currently. This review focuses on the latest findings on the foodborne transmission routes of HAV and HEV and the methods for their detection in different food matrices.

Rodent-borne viruses in the region of Middle East

Rodents are one of the most abundant mammal species in the world. They form more than two-fifth of all mammal species and there are approximately 4600 existing rodent species. Rodents are capable of transmitting deadly diseases, especially those that are caused by viruses. Viruses and their consequences have plagued the world for the last two centuries, three pandemics occurred during the last century only. The Middle East is situated at the crossroads of Africa and Asia, along with the Mediterranean Sea and the Indian Ocean, its geographic importance is gained through the diversity of topographies, biosphere, as well as climate aspects that make the region vulnerable to host emerging diseases. Refugee crises also play a major role in expected epidemic outbreaks in the region. Public health has always been the most important priority, and our aim in this review is to raise awareness among public health organisations across the Middle East about the dangers of rodent borne diseases that have been reported or are suspected to be found in the region.

Geographic and Temporal Variability of Hepatitis E Virus Circulation in the Russian Federation

The factors influencing hepatitis E virus (HEV) circulation remain largely unexplored. We investigated HEV seroprevalence in humans and the prevalence of infection in farm pigs and rabbits in different regions of the Russian Federation, as well as the genetic diversity and population dynamics of the HEV. The anti-HEV IgG antibody detection rates in the general population increase significantly with age, from 1.5% in children and adolescents under 20 years old to 4.8% in adults aged between 20 and 59 years old to 16.7% in people aged 60 years and older. HEV seroprevalence varies between regions, with the highest rate observed in Belgorod Region (16.4% compared with the national average of 4.6%), which also has the country's highest pig population. When compared with the archival data, both increases and declines in HEV seroprevalence have been observed within the last 10 years, depending on the study region. Virus shedding has been detected in 19 out of the 21 pig farms surveyed. On one farm, the circulation of the same viral strain for five years was documented. All the human and animal strains belonged to the HEV-3 genotype, with its clade 2 sequences being predominant in pigs. The sequences are from patients, pigs, and sewage from pig farms clustered together, suggesting a zoonotic infection in humans and possible environmental contamination. The HEV-3 population size that was predicted using SkyGrid reconstruction demonstrated exponential growth in the 1970s-1990s, with a subsequent decline followed by a short rise around the year 2010, the pattern being similar to the dynamics of the pig population in the country. The HEV-3 reproduction number (Re) that was predicted using birth-death skyline analysis has fluctuated around 1 over the past 20 years in Russia but is 10 times higher in Belgorod Region. In conclusion, the HEV-3 circulation varies both geographically and temporally, even within a single country. The possible factors contributing to this variability are largely related to the circulation of the virus among farm pigs.

Low prevalence of hepatitis E virus in the liver of Corsican pigs slaughtered after 12 months despite high antibody seroprevalence

Hepatitis E virus (HEV) infection can be acute and benign or evolve to chronic hepatitis with rapid progression toward cirrhosis or liver failure in humans. Hence, hepatitis E (HE) disease is a major public health concern. In countries where pig populations are highly contaminated with HEV, human cases of HE are mainly foodborne, occurring frequently after consumption of raw or undercooked pork products or liver. Among factors associated to the presence of HEV in pork livers from intensive rearing systems, early slaughter (≤6 months) seems to be major. In Corsica, local pigs are raised in extensive farming systems and slaughtered after 12 months. To evaluate if slaughter of pigs over 12 months reduces the risk of HEV presence in livers, 1197 liver samples were randomly collected in 2 Corsican slaughterhouses. Presence of HEV RNA was detected in liver and HEV seroprevalence was determined in paired serum. The sampling included 1083 livers from animals between 12 and 48 months and 114 livers from animals <12 months. The samples were predominantly from semi-extensive and extensive farms (n = 1154). Estimated HEV seroprevalence was high, that is, >88%, and HEV RNA prevalence in adult pig livers (>12 months old) was low, that is, 0.18%. However, in livers from younger animals (<12 months), including piglets below 6 months old, 5.3% (6/114) of the samples were positive for HEV RNA. Sequences recovered from positive livers belonged to HEV genotype 3c and 3f. The presence of infectious HEV was confirmed in two livers by the detection of HEV replication in HepaRG cell cultures. Thus, this study demonstrates the low prevalence of HEV in livers of pigs over 12 months, even in farms with high HEV circulation. This observation may open new perspectives on the preferential use of livers from animals older than 12 months in raw pork liver products.

High prevalence of acute hepatitis E virus infection in pigs in Dutch slaughterhouses

Hepatitis E is caused by hepatitis E virus (HEV), one of the causes of acute viral hepatitis. Domestic pigs are considered as the main reservoir of HEV-3. The recently reported high prevalence of HEV in liver- and meat products on the Dutch market warranted a cross-sectional prevalence study on HEV infection among 5-6 months old pigs slaughtered in the Netherlands (n = 250). For this, liver, caecum content and blood samples were analyzed for the presence of genomic HEV RNA by RT-PCR. In addition, a serological test was performed to detect HEV IgG. Background information was retrieved on the corresponding farms to evaluate potential risk factors for HEV at pig slaughter age. HEV IgG was detected in sera from 167 pigs (67.6 %). HEV RNA was detected in 64 (25.6 %) caecum content samples, in 40 (16.1 %) serum samples and in 25 (11.0 %) liver samples. The average level of viral contamination in positive samples was log₁₀ 4.6 genome copies (gc)/g (range 3.0-8.2) in caecum content, log₁₀ 3.3 gc/ml (range 2.4-5.9) in serum and log₁₀ 3.2 gc/0.1 g (range 1.7-6.2) in liver samples. Sequence analyses revealed HEV-3c only. Ten times an identical strain was detected in two or three samples obtained from the same pig. Each animal in this study however appeared to be infected with a unique strain. The presence of sows and gilts and welfare rating at the farm of origin had a significant effect (p < 0.05) on the distribution over the four groups representing different stages of HEV infection based on IgG or RNA in caecum and/or serum. The observed proportion of tested pigs with viremia (16 %) was higher than in other reported studies and was interestingly often observed in combination with a high number of HEV genome copies in liver and caecum content as detected by RT-qPCR. Data provided will be useful for risk assessment for food safety of pork products, will provide baseline data for future monitoring of HEV infections in pigs and new thoughts for mitigation strategies.

Dynamic of Hepatitis E Virus (HEV) Shedding in Pigs

Simple Summary

Hepatitis E virus (HEV) is an emerging pathogen, causing an increasing number of autochthonous cases in industrialized countries. In Europe, infections are associated with the zoonotic HEV-3 and HEV-4 genotypes and pigs and wild boars are the main reservoirs. A major concern of infections is linked to its foodborne transmission, due to consumption of raw or undercooked pork products infected by HEV-3 or HEV-4. HEV-3 is widespread in farmed pigs, mainly aged 3–4 months. Besides a decline with age, infected pigs have been observed at slaughterhouses, representing a risk for both the consumers and the workers of the pig industry. HEV is transmitted by the fecal–oral route and shed in feces in large amounts. The risk of viral spreading in farm and presence of infected pigs at slaughtering was evaluated by assessing the quantity and the duration of HEV-3 shedding in feces of infected pigs. Feces of 23 HEV-3 positive pigs were assayed during their fattening, shortly before their slaughtering. Results confirmed a long period of viral shedding in feces with a large amount of the virus released in the environment (mean 10⁵ GC/g). Prevalence and quantity of the virus declines with the age of animals. The study provides information on the dynamic of the infection in pigs, important to prevent HEV occurrence and circulation in farms.

Abstract

Genotype 3 of hepatitis E virus (HEV-3) is the most common in Europe in both humans and pigs. HEV-3 strains are zoonotic, and foodborne cases associated with consumption of raw and undercooked pork products, mainly liver sausages, have been described. HEV-3 circulates largely in European pig farms, maybe due to its long persistence in the environment. Animals get infected around 3–4 months of age; shortly after, the infection starts to decline up to the age of slaughtering (8–9 months of age in Italy). With the purpose to understand the duration in farmed pigs of the shedding of the virus and its quantity, HEV-RNA detection was performed by Real-time RT-PCR from feces collected individually from two groups of 23 pigs. Sampling was conducted for 4 months shortly before slaughtering age. At 4-months-old, all animals were shedding HEV-3 to high load around 10⁵ genome copies per gram (GC/g). Prevalence was higher in growers than in fatteners, with most of the pigs still positive around 166 days of age. Beyond some difference among individual pigs, the amount of HEV in feces decreased with the age of animals. The longest fattening period should ensure a lower risk of HEV shedder animals at slaughter, reducing the risk of food contamination.

Screening of Swiss Pig Herds for Hepatitis E Virus: A Pilot Study

Hepatitis E virus (HEV) is an important cause of acute hepatitis in humans worldwide. In industrialised countries, most infections are caused by the zoonotic genotype 3. The main reservoir was found in pigs, with fattening pigs as the main shedders. The aim of this study was to establish a screening tool to detect HEV in pig farms. HEV-positive samples were sequenced using Sanger sequencing. First, different sample materials, including floor swabs, slurry, dust swabs and faeces were tested for HEV. Floor swabs turned out to give the best results and, in the form of sock swabs, were used for the screening of Swiss pig herds. A total of 138 pig farms were tested, with a focus on fattening pigs. Overall, 81 farms (58.8%) were HEV positive. Most sequences belonged to subtype 3h, in which they formed a specific cluster (Swiss cluster). In addition, subtype 3l and two unassigned sequences were detected. As a conclusion, sock swabs were found to be a helpful tool to screen pig herds for HEV and establish a sequence collection that may enable molecular epidemiology and support outbreak investigation and prevention.

Advanced Research in Porcine Reproductive and Respiratory Syndrome Virus Co-infection With Other Pathogens in Swine

The porcine reproductive and respiratory syndrome virus (PRRSV) is the pathogen causing epidemics of porcine reproductive and respiratory syndrome (PRRS), and is present in every major swine-farming country in the world. Previous studies have demonstrated that PRRSV infection leads to a range of consequences, such as persistent infection, secondary infection, and co-infection, and is common among pigs in the field. In recent years, coinfection of PRRSV and other porcine pathogens has occurred often, making it more difficult to define and diagnose PRRSV-related diseases. The study of coinfections may be extremely suitable for the current prevention and control in the field. However, there is a limited understanding of coinfection. Therefore, in this review, we have focused on the epidemiology of PRRSV coinfection with other pathogens in swine, both in vivo and in vitro.

Global molecular diversity of Hepatitis E virus in wild boar and domestic pig

Our study aim was to describe and characterize the global Hepatitis E virus (HEV) molecular and genotype geographical distribution in domestic pig and wild boar, which could facilitate the traceability of human cases. We performed a systematic sequence search for HEVs identified in domestic pig and wild boar from the available data in GenBank. Only sequences with lengths greater than 300 nt were included. For all sequences, the sequence length, host (i.e., domestic pig or wild boar), country of origin, and HEV genotype/subtype were recorded. Genotypes were assigned by the HEVnet typing tool. The genotype distributions were described by country and host. In countries with sequences available for both species, the genotype coincidences between both animal populations were analyzed. A total of 1404 viral sequences were included: 32.6% from wild boar and 67.4% from domestic pig. Most sequences were consistent with HEV genotype 3 (n = 1165). Genotype 4 was represented by 193 sequences, while genotypes 5 and 6 were represented by only 6 sequences. Sequences were identified in 39 countries, which included all continents except Antarctica. The genotypes with a wide distribution were 3a and 3f. Twenty-five countries had sequences that were found only in domestic pig, three countries only in wild boar, and 11 countries had sequences in both populations. In all countries with available sequences in both populations, the same viral genotype was identified. Our study shows that the number of swine HEV sequences is small, which limits direct comparisons with the sequences identified in humans. The global distribution of genotype 3, together with the wide distribution of genotype 4 in Asia, strongly limits the interpretation of the molecular analysis in the absence of an epidemiological survey of the cases. Increased HEV sequencing in swine should be a priority.

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Our study shows that the number of swine HEV sequences is small.

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The global distribution of genotype 3 strongly limits the interpretation of the molecular analysis.

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Increased HEV sequencing in swine should be a priority.

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

In humans, hepatitis E virus (HEV) is responsible for an acute enterically transmitted hepatitis, which can become chronic in immune-compromised patients. Genotypes 3 and 4 (HEV-3 and HEV-4) are zoonotic, and domestic pigs and wild boar are the main reservoirs. The occurrence of autochthonous cases in Europe, which have been increasing over the last 10 years, has been associated with food-borne zoonotic transmission of HEV-3, mainly linked to consumption of undercooked or raw pork products (sausages containing liver) and wild boar meat. Zoonotic HEV-3 strains are widespread on pig farms, but little information is available on the dynamic of HEV-3 infection within farms, among pigs. The aims of this study were to evaluate the prevalence of the infection among pigs of different ages along the production chain by the zoonotic HEVs, and to evaluate how long the virus may persist in the farm environment. The presence of HEV-RNA was investigated by real-time reverse transcription PCR (RT-PCR) in 281 test faecal pools over 19 months (2017-2019) on a two-site farrow-to-finish farm (about 1,000 sows), in Northern Italy. A total of 67/281 test faecal pools (23.8%) resulted positive for the presence of HEV-RNA (site 1: 59/221, 26.7%; site 2: 8/60, 13.3%). Nucleotide sequencing revealed a unique HEV-3 viral variant circulating during 19 months of surveillance. The same HEV-3 strain was detected in the same farm on 2012, indicating the persistence of the same virus over 7 years, and highlighting the role of the environment as a continuous source of infection on pig farms. The results confirmed the circulation of the zoonotic genotype HEV-3 in pigs before slaughtering.

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

Background

Hepatitis E virus (HEV) genotype 3 and 4 is a zoonosis that causes hepatitis in humans. Humans can become infected by consumption of pork or contact with pigs. Pigs are the main reservoir of the virus worldwide and the virus is present on most pig farms.

Main body

Though HEV is present on most farms, the proportion of infected pigs at slaughter and thus the level of exposure to consumers differs between farms and countries. Understanding the cause of that difference is necessary to install effective measures to lower HEV in pigs at slaughter. Here, HEV studies are reviewed that include infection dynamics of HEV in pigs and on farms, risk factors for HEV farm prevalence, and that describe mechanisms and sources that could generate persistence on farms. Most pigs become infected after maternal immunity has waned, at the end of the nursing or beginning of the fattening phase. Risk factors increasing the likelihood of a high farm prevalence or proportion of actively infected slaughter pigs comprise of factors such as farm demographics, internal and external biosecurity and immunomodulating coinfections. On-farm persistence of HEV is plausible, because of a high transmission rate and a constant influx of susceptible pigs. Environmental sources of HEV that enhance persistence are contaminated manure storages, water and fomites.

Conclusion

As HEV is persistently present on most pig farms, current risk mitigation should focus on lowering transmission within farms, especially between farm compartments. Yet, one should be aware of the paradox of increasing the proportion of actively infected pigs at slaughter by reducing transmission insufficiently. Vaccination of pigs may aid HEV control in the future.

Variations among Viruses in Influent Water and Effluent Water at a Wastewater Plant over One Year as Assessed by Quantitative PCR and Metagenomics

Influent wastewater and effluent wastewater at the Rya treatment plant in Gothenburg, Sweden, were continuously monitored for enteric viruses by quantitative PCR (qPCR) during 1 year. Viruses in effluent wastewater were also identified by next-generation sequencing (NGS) in samples collected during spring, early summer, and winter. Samples of incoming wastewater were collected every second week. Seasonal variations in viral concentrations in incoming wastewater were found for noroviruses GII, sapovirus, rotavirus, parechovirus, and astrovirus. Norovirus GI and GIV and Aichi virus were present in various amounts during most weeks throughout the year, while hepatitis A virus, enterovirus, and adenovirus were identified less frequently. Fluctuations in viral concentrations in incoming wastewater were related to the number of diagnosed patients. The viruses were also detected in treated wastewater, however, with a 3- to 6-log₁₀ reduction in concentration. Seven different hepatitis E virus (HEV) strains were identified in the effluents. Five of these strains belonged to genotype 3 and have been isolated in Sweden from swine, wild boars, and humans and in drinking water. The other two strains were divergent and had not been identified previously. They were similar to strains infecting rats and humans. Surveillance of enteric viruses in wastewater is a tool for early detection and follow-up of gastroenteritis outbreaks in society and for the identification of new viruses that can cause infection in humans.IMPORTANCE Both influent wastewater and treated wastewater at a wastewater treatment plant (WWTP) contain a high variety of human viral pathogens with seasonal variability when followed for 1 year. The peak of the amount of 11 different viruses in the inlet wastewater preceded the peak of the number of diagnosed patients by 2 to 4 weeks. The treatment of wastewater reduced viral concentrations by 3 to 6 log₁₀ Despite the treatment of wastewater, up to 5 log₁₀ virus particles per liter were released from into the surrounding river. Hepatitis E virus (HEV) strains previously identified in drinking water and two new strains, similar to those infecting rats and humans, were identified in the treated wastewater released from the WWTP.

Hepatitis E virus genotype 3 strains and a plethora of other viruses detected in raw and still in tap water

In this study, next generation sequencing was used to explore the virome in 20L up to 10,000L water from different purification steps at two Swedish drinking water treatment plants (DWTPs), and in tap water. One DWTP used ultrafiltration (UF) with 20 nm pores, the other UV light treatment after conventional treatment of the water. Viruses belonging to 26 different families were detected in raw water, in which 6-9 times more sequence reads were found for phages than for known environmental, plant or vertebrate viruses. The total number of viral reads was reduced more than 4-log10 after UF and 3-log10 over UV treatment. However, for some viruses the reduction was 3.5-log10 after UF, as for hepatitis E virus (HEV), which was also detected in tap water, with sequences similar to those in raw water and after treatment. This indicates that HEV had passed through the treatment and entered into the supply network. However, the viability of the viruses is unknown. In tap water 10-130 International Units of HEV RNA/mL were identified, which is a comparable low amount of virus. The risk of getting infected through consumption of tap water is probably negligible, but needs to be investigated. The HEV strains in the waters belonged to subtypes HEV3a and HEV3c/i, which is associated with unknown source of infection in humans infected in Sweden. None of these subtypes are common among pigs or wild boar, the major reservoirs for HEV, indicating that water may play a role in transmitting this virus. The results indicate that monitoring small fecal/oral transmitted viruses in DWTPs may be considered, especially during community outbreaks, to prevent potential transmission by tap water.

Tackling hepatitis E virus spread and persistence on farrow-to-finish pig farms: Insights from a stochastic individual-based multi-pathogen model

Hepatitis E virus (HEV) is a zoonotic agent of which domestic pigs have been recognised as the main reservoir in industrialised countries. The great variability in HEV infection dynamics described on different pig farms may be related to the influence of other pathogens, and in particular viruses affecting pigs' immune response. The objective of this study was to develop a multi-pathogen modelling approach to understand the conditions under which HEV spreads and persists on a farrow-to-finish pig farm taking into account the fact that pigs may be co-infected with an intercurrent pathogen. A stochastic individual-based model was therefore designed that combines a population dynamics model, which enables us to take different batch rearing systems into account, with a multi-pathogen model representing at the same time the dynamics of both HEV and the intercurrent pathogen. Based on experimental and field data, the epidemiological parameters of the HEV model varied according to the pig's immunomodulating virus status. HEV spread and persistence was found to be very difficult to control on a farm with a 20-batch rearing system. Housing sows in smaller groups and eradicating immunomodulating pathogens would dramatically reduce the prevalence of HEV-positive livers at slaughter, which would drop from 3.3% to 1% and 0.2% respectively (p-value < 0.01). It would also decrease the probability of HEV on-farm persistence from 0.6 to 0 and 0.34 respectively (p-value < 0.01) on farms with a 7 batch rearing system. A number of farming practices, such as limiting cross-fostering, reducing the size of weaning pens and vaccinating pigs against immunomodulating viruses, were also shown to be pivotal factors for decreasing HEV spread and persistence.

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

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.