Wild Boar as a Sylvatic Reservoir of Hepatitis E Virus in Poland: A Cross-Sectional Population Study

Molecular Characterization and Phylogenetic Analysis of Hepatitis E Virus (HEV) Strains from Pigs Farmed in Eight European Countries between 2020 and 2022

In high-income countries, the hepatitis E virus (HEV) is considered an emerging threat causing autochthonous acute hepatitis in humans, with an increased number of reported cases over the last 10 years and related increased burden of chronic hepatitis in immunocompromised and transplant patients. Pigs are the main reservoir of the HEV-3 genotype, which is the most common in Europe, and can be transmitted to humans through the consumption of raw and undercooked pork products. Extensive sequencing revealed the existence of several HEV-3 subtypes in both humans and pigs, confirming a broad heterogeneity of the virus, with some subtypes, such as 3e, 3f, and 3c, which are predominant in Europe. In this study, 291 HEV sequences were obtained from pig feces sampled in more than 74 farms located in Austria, Bulgaria, Czech Republic, Germany, Italy, Poland, the United Kingdom, as well as an unknown number of farms in Netherlands. Of the 99 nonidentical sequences (99/291), 90 were assigned to seven established HEV-3 subtypes: 3a, 3c, 3e, 3f, 3g (here named 3g-like), 3i, and 3l (named 3l-like), already described in Europe, while nine sequences of HEV-3 could not be assigned to any existing subtype (here named 3  ∗ ). The 3e subtype was the most common, detected in six out of eight countries, followed by 3f and 3c, which were also present in several countries; 3g-like, 3i, and 3l-like subtypes showed only a limited circulation. The distribution of frequently (3e, 3f, and 3c) and rarely (3g-like, 3i, and 3l-like) detected HEV-3 subtypes in pigs was correlated with their detection rates in human patients in Europe. The results from this study confirm the wide circulation of several HEV-3 strains in European pigs and confirm that sequencing is needed to monitor the different strains and to identify possible zoonotic transmission paths.

Hepatitis E Virus in the Wild Boar Population: What Is the Real Zoonotic Risk in Portugal?

Hepatitis E virus (HEV) is an important zoonosis in wild boar. Reported zoonotic cases are mainly associated with the consumption of raw/undercooked meat and/or liver. This study aims to determine the occurrence of HEV in the Portuguese wild boar population. During the hunting season 2021/2022, 123-matched samples (liver, faeces, and blood) were collected from hunted wild boars throughout Portugal. An RT-PCR assay tested liver and faeces samples to detect HEV-RNA. From blood samples, an ELISA test was performed. Only one liver sample was positive for HEV (0,8%) and one other from faeces. A total of 34 sera were seropositive (26.7%). At the same time, in a survey of 106 hunters, 21 consumed/ate the liver of wild boars (19.8%). Only three recognised the possibility of consuming it undercooked. Contrary to previous studies in Portugal, the prevalence of HEV in liver and faeces is low, but the seropositivity is higher. But, when analyzing in detail, it could be observed that an HEV hotspot exists in the southeast of central Portugal and that it is a zoonotic risk for hunters of this region. The data of this study reinforce the importance of including HEV in surveillance programs for wildlife diseases to expand the potential zoonotic information.

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.

Presence of porcine cytomegalovirus, a porcine roseolovirus, in wild boars in Italy and Germany

Porcine cytomegalovirus (PCMV), a porcine roseolovirus (PRV) that is closely related to human herpesviruses 6 and 7, is commonly found in commercial pigs. PCMV/PRV is important in xenotransplantation, because in preclinical trials in which pig organs were transplanted into non-human primates, transmission of PCMV/PRV was shown to be associated with significantly reduced survival of the xenotransplants. PCMV/PRV was also transmitted in the first transplantation of a pig heart into a human patient worldwide and apparently contributed to the death of the patient. The prevalence of PCMV/PRV in wild boars is largely unknown. In this study, we screened wild boars from several areas of northern Italy and Germany to test for the presence of PCMV/PRV using PCR-based and Western blot assays. By Western blot analysis, 54% and 82% of Italian and German wild boars, respectively, were found to be PCMV/PRV positive, while 36% and 60%, respectively, tested positive by real-time polymerase chain reaction (PCR). These data indicate that the virus is common in German and Italian wild boars and that the Western blot assay detected a PCMV/PRV infection more often than did real-time PCR. The data also indicate that pigs raised for xenotransplantation should be protected from contact with materials from wild boars and commercial pigs.

Hepatitis E virus in the endangered Iberian lynx (Lynx pardinus)

Hepatitis E virus (HEV) is an emerging zoonotic pathogen in Europe. In the Iberian Peninsula, wild boar (Sus scrofa) is considered the main wildlife reservoir of HEV. This wild ungulate shares habitat and resources with other potential HEV carriers in Iberian Mediterranean ecosystems, although information about the role of such sympatric species in the HEV epidemiological cycle is still very limited. The aims of the present large-scale, long-term study were: (1) to determine the seroprevalence and prevalence of HEV in both free-living and captive populations of the Iberian lynx (Lynx pardinus), the most endangered felid in the world; (2) to determine potential risk factors associated with HEV exposure in this species and (3) to evaluate the dynamics of seropositivity in longitudinally sampled animals during the study period. Between 2010 and 2021, serum samples from 275 Iberian lynxes were collected in free-ranging and captive populations across the Iberian Peninsula. Forty-four of the 275 lynxes were also longitudinally sampled during the study period. A double-antigen sandwich ELISA was used to test for the presence of antibodies against HEV. A subset of seropositive samples was analysed by Western blot (WB) assay to confirm exposure to HEV. In addition, serum, liver and/or faecal samples from 367 individuals were tested for orthohepevirus RNA by RT-PCR. A total of 50 (18.2%; 95% CI: 14.1-23.2) of the 275 animals analysed had anti-HEV antibodies by ELISA. Exposure to HEV was confirmed by WB in most of the ELISA-positive Iberian lynxes analysed. Significantly higher seroprevalence was found in captive (33.6%) compared to free-ranging (7.4%) individuals. Within captive population, the GEE model identified 'age' (senile, adult and subadult) as risk a factor potentially associated with HEV exposure in the Iberian lynx. Thirteen (29.5%) of 44 longitudinally surveyed individuals seroconverted against HEV during the study period. HEV RNA was detected in the faeces of one (1/364; 0.3%; 95% CI: 0.0-0.8) free-ranging adult animal sampled in 2021. Phylogenetic analysis showed that the sequenced strain belongs to HEV-3f subtype and shared a high nucleotide sequence identity (97-99.6%) with human HEV-3f sequences from Spain and France. To the best of the authors' knowledge, this is the first survey study on HEV in the Iberian lynx and the first molecular report of HEV-A infection in free-ranging felines. Our results indicate high exposure to HEV-3 in Iberian lynx populations, particularly those kept in captivity. The serological results suggest widespread but not homogeneous circulation of HEV in Iberian lynx populations. Further studies are required to assess the epidemiological role of this endangered species as a potential spillover host of HEV.

Genetic characterization of hepatitis E virus from wild boar in China

Hepatitis E virus (HEV), the causative agent of hepatitis E (HE), is classified into four major genotypes (1-4), with wild boar being the main natural reservoir for genotypes 3 and 4. However, little is known about the prevalence of HEV infection in wild boars in China. In this study, RT-nested PCR and RT-quantitative PCR were used to detect the HEV RNA in tissue samples taken from 331 free-ranging wild boars collected between 2018 and 2020 from 24 regions across China, and the partial ORF2 genes or complete genomes of the positive samples were sequenced. Furthermore, antibodies against HEV in 216 serum samples from wild boars were tested by ELISA. As a result, HEV RNA was detected in nine out of 331 liver samples of wild boars (2.72%), which were distributed in eight regions. Genetic and evolutionary analysis of partial ORF2 sequences indicated that the HEV strains identified in this study share 83.9%-100% nucleotide sequence identity and belong to subtypes 4d (n = 6), 4g (n = 2), and 4h (n = 1), and similar phylogeny was obtained using the complete genome sequences of seven wild boar HEV strains. Additionally, the HEV viral loads were higher in the liver than in other tissues and blood. Moreover, 61 out of 216 sera (28.2%) from wild boars tested positive for anti-HEV antibodies. To our knowledge, this is the first study to report the epidemiological situations of HEV infections in free-ranging wild boars in China, and the obtained data are valuable for prevention and control of HE.

Nationwide survey of hepatitis E virus infection among wildlife in Japan

In Japan, hepatitis E virus (HEV) causes hepatitis in humans through the consumption of raw or undercooked meat, including game meat. In the present study, nationwide surveillance of HEV infection among a total of 5,557 wild animals, including 15 species, was conducted in Japan. The prevalence of anti-HEV antibodies in wild boar was 12.4%, with higher positive rates in big boars (over 50 kg, 18.4%) than in small individuals (less than 30 kg, 5.3%). Furthermore, HEV RNA was more frequently detected in piglets than in older boars. Interestingly, the detection of HEV among wildlife by ELISA and RT-PCR suggested that HEV infection in Sika deer was a very rare event, and that there was no HEV infection among wild animals except for wild boar, Sika deer and Japanese monkeys. In conclusion, wild boar, especially piglets, are at high risk of HEV infection, while other wild animals showed less risk or no risk of HEV transmission.

A systematic review and meta-analysis of hepatitis E virus (HEV) in wild boars

This systematic review and meta-analysis summarize the available information on Hepatitis E virus (HEV) -specific antibody seroprevalence and HEV RNA prevalence in wild boar, one of the most abundant game species worldwide. A literature search (CAB Abstracts, Web of Science, Embase and Scopus) was performed to find relevant peer-reviewed works published during the period 1990-2020. A random-effect model was carried out to calculate the pooled HEV-specific antibody seroprevalence and HEV RNA prevalence estimates with 95% confidence intervals, and I2 statistic was used to assess the heterogeneity of the data. Values by subgroups were compared according to the geographical area, age class (≤ 12 months old and > 12 months old), and sample type (bile, faeces, liver, meat/muscle, serum). Sixty-nine publications were selected, with the majority of the studies from Southern Europe (n = 27). The pooled HEV-specific antibody seroprevalence in wild boar was 28% (CI95% 23-34) and the HEV RNA prevalence 8% (CI95% 6-10). The analysis highlighted a significant heterogeneity among the estimates from the included studies (I2 = 98% and I2 = 95% for HEV-specific antibody seroprevalence and viral prevalence respectively). The moderator analysis indicated a statistically significant difference (p-value = 0.03) for the HEV RNA prevalence according to the sample type, with the highest value in bile (17%, CI95% 9-27), followed by liver (10%, CI95% 7-14), serum (7%, CI95% 4-10), faeces (5%, CI95% 2-9), and meat/muscle (3%, CI95% 0.04-10). Finally, the HEV RNA prevalence in Europe (8.7, CI95% 6.7-11) was significantly (p-value = 0.04) higher than in Asia (4, CI95% 0.6-8). The analysis highlights the important role of wild boar in the epidemiology of HEV.

Analysis of seroprevalence data on Hepatitis E virus and Toxoplasma gondii in wild ungulates for the assessment of human exposure to zoonotic meat-borne pathogens

Seroprevalence data for Toxoplasma gondii and Hepatitis E virus (HEV) in wild boar (Sus scrofa), roe deer (Capreolus capreolus), red deer (Cervus elaphus), mouflon (Ovis aries/musimon) and chamois (Rupicapra rupicapra) hunted/culled in northern Italy were used to fit seroprevalence distributions describing the exposure and co-exposure of the species to the two pathogens. The higher proportion of T. gondii and HEV seropositive animals was observed in wild boars with point estimate seroprevalence of 49% (N = 331) and 15% (N = 326) respectively. Data allowed comparisons by area (pre-Alpine Vs Alpine environment) for roe deer, red deer and mouflons. Contrasts between the distributions describing the uncertainty in seroprevalence suggest roe deer, red deer and mouflons have higher probability of being seropositive to T. gondii in pre-Alps. When considering HEV, few seropositive animals were detected and contrasts were symmetrically centred to zero for roe deer and red deer; mouflons shown higher probability of being seropositive in Alpine environment. HEV seropositive animals also included chamois (P = 5.1%, N = 97) in the Alpine districts, confirming circulation of HEV in remote areas. Evidence of HEV and T. gondii co-exposure was limited except for wild boars where it was observed in 30 samples representing 60% of the overall HEV-positive samples. Seroprevalence data of single infection and co-infection are extremely useful to investigate circulation of zoonotic pathogens in wild animals and estimate the foodborne risk of human exposure, however, these type of data do not directly translate into the presence/absence of the pathogen in seropositive and seronegative animals. At benefit of future development of quantitative risk assessments aiming at estimating the risk of human infection/co-infection via consumption of game meat, we developed and made available an online application that allows estimating the probability of the pathogen(s) being present as a function of seroprevalence data.

Porcine Blood and Liver as Sporadic Sources of Hepatitis E Virus (HEV) in the Production Chain of Offal-Derived Foodstuffs in Poland

Pig's blood and liver are valuable edible slaughter by-products which are also the major ingredients of offal-derived foodstuffs. The aim of the study was an evaluation of the occurrence of hepatitis E virus (HEV) and porcine adenovirus (pAdV) as an index virus of faecal contamination in pig's blood and liver for human consumption. In total, 246 samples of retail liver (n = 100) and pooled pig's blood (n = 146) were analysed for the presence of HEV and pAdV. Blood samples were individually collected from 1432 pigs at slaughter age. Viral genomic material, including RNA of a sample process control virus was isolated from food samples using a QIAamp® Viral RNA Mini Kit. Virus-specific IAC-controlled real-time PCR methods were used for detection of target viruses. HEV RNA was found in 6 (2.4%; 95% CI: 0.9-5.2) out of 246 samples of tested foodstuffs. The virus was detected in pig's blood (3.4%; 95% CI: 1.1-7.8) and liver (1.0%; 95% CI: 0.0-5.0) with no significant differences observed in the frequency of its occurrence between the two by-products (t = 1.33; p = 0.182 > 0.05); however PAdV was detected more frequently in pig's blood than in liver (t = 4.65; p = 0.000 < 0.05). The HEV strains belonged to the 3f and 3e subtype groups and the pAdV strains were assigned to serotype 5. PAdV was detected in pigs regardless of the farm size from which they originated. The number of animals raised on the farm (the farm size) had no influence on the occurrence of HEV or pAdV infections in pigs (F = 0.81, p = 0.447 > 0.05 for HEV; F = 0.42, p = 0.655 > 0.05 for pAdV). Although HEV was detected in pig's offal only sporadically, consumers cannot treat its occurrence with disregard as it demonstrates that HEV-contaminated pig tissues can enter the food chain.

Genetic Diversity and Epidemiological Significance of Wild Boar HEV-3 Strains Circulating in Poland

The wild boar is the most important reservoir of zoonotic HEV-3 strains among different wildlife species. The aim of the study was subtype identification of wild boar HEV-3 strains circulating in Poland. Wild boar liver was used in the study in the form of homogenates prepared from 57 samples positive for HEV in a real-time RT-PCR. These samples were collected from juvenile and adult wild boars hunted in the jurisdictions of different Regional Directorates of State Forests (RDSF) across Poland. Subtype identification of detected HEV strains was based on a phylogenetic analysis of the most conserved HEV ORF2 genome fragment. Out of 57 tested samples, consensus HEV ORF2 sequences of 348 bp were obtained for 45 strains. Nineteen strains were identified and belonged to the HEV gt 3a and 3i subtypes, whereas 26 were not assigned to any virus subtype. HEV gt 3i strains prevailed in the Polish wild boar population, 16 of such were identified, and they were significantly more often observed in the RDSF Katowice area (χ² = 28.6, p = 0.027 (<0.05)) compared to other regions of the country. Circulation of 3a strains was limited only to the RDSF Gdańsk territory (χ² = 48, p = 0.000 (<0.05)). The virus strains detected in the Polish population of wild boars representing previously identified HEV subtypes in wild boars, pigs, or humans in Europe are of epidemiological importance for public health.

Long-Term Determinants of the Seroprevalence of the Hepatitis E Virus in Wild Boar (Sus scrofa)

Simple Summary

The hepatitis E virus (HEV) is an emerging multi-host pathogen whose main reservoir is suids, and the leading cause of acute viral hepatitis in humans. This study evaluates the main long-term drivers of the exposure to HEV are in the wild boar population from Doñana National Park (southwestern Spain) during a 13-year period (2005–2018). For this purpose, we assay sera from 700 wild boar in which anti-HEV antibodies are widely distributed (46.7 ± 3.8%, 327 out of 700 sampled). The observed marked interannual fluctuations could be explained by the variations in the population control of the wild boar during the study period and its impact on abundance rates. Several factors operating in the medium and long-term (individual, environmental, populational and stochastic) and their interplay explained the exposure to HEV in wild boar. The preferential use of certain areas by wild boar together with its abundance and the meteorological conditions may be behind the level of exposure. Wild boar population control remains a challenge at the international level, and an increase of shared pathogen-related conflicts associated with this species is expected, as exemplified by HEV.

Abstract

The hepatitis E virus (HEV) is an emerging zoonotic pathogen whose main reservoir is suids. Most of the ecological and epidemiological aspects of its sylvatic cycle remain unknown. Thus, in this work, we study the drivers of HEV exposure in the wild boar population of Doñana National Park (DNP, southwest Spain) operating in the medium and long-term (2005–2018). Anti-HEV antibodies are widely distributed throughout the wild boar (46.7 ± 3.8%, 327 out of 700 sampled), showing a statistically significant age-increasing pattern. The temporal pattern displayed important interannual fluctuations. This could be mediated by marked variations in the population control of the wild boar, and subsequent changes in abundance rates, and its interplay with climatic conditions; as wet years together with a low abundance of wild boar led to the lowest seroprevalence. The fact that seroprevalence is high during conditions of high abundance, and not affected by rainfall level, is probably due to the increased interactions among the animals, and possibly, the subsequent higher environmental contamination with HEV particles. The proximity to the marshland (the main water body of the study area) is associated with a higher risk of testing positive, which is probably mediated by the preferential use of this area during the dry season and the favourable environmental conditions for the survival of HEV particles. A deeper understanding of the epidemiology of HEV in host communities deserves future research concerning other susceptible species. Most importantly, wild boar population control remains a challenge at the international level, and an increase of shared pathogen-related conflicts associated with this species is expected, as exemplified by HEV. Therefore, surveillance of wild boar diseases, including integrated population monitoring and sustainable population control programmes, will be essential to control the associated risks.

Hepatitis E Virus in Croatia in the "One-Health" Context

Hepatitis E virus (HEV) is the most common cause of viral hepatitis globally. The first human case of autochthonous HEV infection in Croatia was reported in 2012, with the undefined zoonotic transmission of HEV genotype 3. This narrative review comprehensively addresses the current knowledge on the HEV epidemiology in humans and animals in Croatia. Published studies showed the presence of HEV antibodies in different population groups, such as chronic patients, healthcare professionals, voluntary blood donors and professionally exposed and pregnant women. The highest seroprevalence in humans was found in patients on hemodialysis in a study conducted in 2018 (27.9%). Apart from humans, different studies have confirmed the infection in pigs, wild boars and a mouse, indicating the interspecies transmission of HEV due to direct or indirect contact or as a foodborne infection. Continued periodical surveys in humans and animals are needed to identify the possible changes in the epidemiology of HEV infections.

Hepatitis E Virus RNA Presence in Wild Boar Carcasses at Slaughterhouses in Italy

Simple Summary

Hepatitis E virus (HEV) is a worldwide diffused pathogen responsible for acute hepatitis of humans. Transmission of the pathogen is mostly related to the consumption of contaminated food and water. Although initially the disease was contained in developing countries, in recent years autochthonous infections have been reported in several industrialised countries. A different epidemiological pattern of transmission has been highlighted; while in Africa and Asia transmission is mainly due to waterborne outbreaks caused by low sanitation standards, in Europe and other industrialised countries, the disease has mainly spread due to consumption of raw or undercooked meat and seafood. Although HEV has been identified in several domestic and wild animal species, pigs and wild boar, appear to play a distinct role mainly acting as a reservoir of the pathogen. In this study, we monitored the presence of HEV in carcasses and livers of wild boar sampled in Tuscany at the slaughterhouse following hunting activities. Our data indicate the presence of the pathogen in the liver and the carcasses, suggesting cross-contamination. This evidence highlights the importance of maintaining safety control measures to avoid the spreading of HEV infection.

Abstract

Hepatitis E virus (HEV) is a waterborne and foodborne pathogen largely spread around the world. HEV is responsible for acute hepatitis in humans and it is also diffused in domestic and wild animals. In particular, domestic pigs represent the main reservoir of the infection and particular attention should be paid to the consumption of raw and undercooked meat as a possible zoonotic vehicle of the pathogen. Several studies have reported the presence of HEV in wild boar circulating in European countries with similar prevalence rates. In this study, we evaluated the occurrence of HEV in wild boar hunted in specific areas of Tuscany. Sampling was performed by collecting liver samples and also by swabbing the carcasses at the slaughterhouses following hunting activities. Our data indicated that 8/67 (12%) of liver samples and 4/67 (6%) of swabs were positive for HEV RNA. The presence of HEV genome on swabs indicates the possible cross-contamination of carcass surfaces during slaughtering procedures. Altogether, our data indicated that it is essential to promote health education programmes for hunters and consumers to limit the diffusion of the pathogen to humans.