Molecular and serological survey of hepatitis E virus infection among domestic pigs in Inner Mongolia, China

First Seroepidemiological Investigation of Hepatitis E Virus Infection in Backyard Pigs from Northeastern India: Prevalence and Associated Risk Factors

Hepatitis E virus (HEV) is the leading cause of acute viral hepatitis globally, with zoonotic potential, and pigs are considered the major reservoir. To determine the seroprevalence of HEV infection in pigs reared in backyard conditions in the northeastern region of India, blood samples were collected from 400 pigs from five northeastern states (80 samples from each state) and tested for IgG antibodies against HEV using an ELISA assay. Questionnaires on farm characteristics and management practices were completed, and risk factors associated with HEV were studied using univariate and multivariate analysis. The apparent seroprevalence of HEV infection was 51% (46.1-55.9, 95% CI), with a true prevalence of 52.98% (47.22-58.75, 95% CI). The risk factors significantly associated with higher HEV seropositivity were as follows: lack of disinfection (OR 4.65), feeding swill (restaurant and bakery waste) (OR 2.55), failure to follow the all-in-all-out production system (OR 3.47), and medium holding size (OR 9.83), which refers to mixed rearing of younger and older age groups. This study demonstrates that HEV is widespread among pigs reared in northeastern India. The risk factor analysis conducted in this study provides valuable insights into the prevalence of HEV in the region.

A Randomized Large-Scale Cross-Sectional Serological Survey of Hepatitis E Virus Infection in Belgian Pig Farms

Hepatitis E virus (HEV) is the causative agent of hepatitis E disease in humans. While sporadic HEV infections, which occur in industrialised countries and are typically due to HEV genotypes 3 or 4, are asymptomatic and self-limiting, a chronic form of the disease can lead to liver cirrhosis in immunocompromised individuals. Pigs share HEV 3 and 4 genotypes and are thus considered a major animal reservoir for human infection. A subset of animals has been shown to carry HEV particles at the age of slaughter, rendering raw or undercooked pig products potential vectors for human infection. To provide an overview of the current dissemination of HEV in Belgian pig herds, this study was designed as a randomized, robust, large-scale, cross-sectional, serological survey. HEV genotypes and subtypes recently circulating in Belgium (2020-2021) were investigated. Sample stratification as well as epidemiological investigation through the available demographic data of the sampled herds showed that HEV widely circulated in the Belgian pig population during this time and that a change in the circulating HEV strains may have occurred in the last decade. Herd size and type were identified as risk factors for HEV herd-seropositivity. Identifying farms at risk of being HEV-positive is an important step in controlling HEV spread and human infection.

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.

Prevalence of hepatitis E virus among swine in China from 2010 to 2019: A systematic review and meta-analysis

Hepatitis E virus (HEV) is a zoonotic pathogen that has spread worldwide. The HEV reservoir associated with livestock hepatitis E poses a huge threat to public health. Awareness of the prevalence and spatial distribution of livestock hepatitis E is valuable to prevent and control diseases caused by HEV, especially human hepatitis E infection. Currently, swine, including pigs (Sus scrofa), are recognized as the major reservoir of HEV. Therefore, we conducted a systematic review and meta-analysis to evaluate the pooled prevalence of HEV among swine in China. A total of 71 published papers on HEV infection in swine in China (including data from 49,523 animals) from January 1, 2010 to December 31, 2019 met the standard after searching five databases including the Technology Periodical Database, the Wan Fang Database, the China National Knowledge Infrastructure, PubMed, and ScienceDirect. A random effects model was used to calculate the pooled prevalence of HEV in swine. The results showed that the seroprevalence was 48.0% (95% confidence interval (CI) 39.6-56.9) and the prevalence of HEV RNA was 14.4% (95% CI 10.7-18.5). The estimated overall prevalence was 34.1% (95% CI 27.2-41.4). Central China (68.0%, 95% CI 42.2-89.1) had a significantly higher prevalence than other regions. In the publication year subgroup, the prevalence in 2016 or later (27.2%, 95% CI 19.3-36.0) was significantly lower than that in 2011 or earlier (49.0%, 95% CI 36.2-61.8). The prevalence of IgG (42.9%, 95% CI 31.7-54.6) was significantly higher than that of IgM (4.9%, 95% CI 1.6-9.7). Suckling piglets (15.6%, 95% CI 6.6-27.1) had a lower prevalence compared with that in other age groups. In all sample types, body fluids showed the highest prevalence (50.5%, 95% CI 41.7-59.3). Moreover, the pooled prevalence of HEV in boars was higher than that in sows (35.4% > 17.3%). The analysis suggested that HEV infection is common among swine in China. Further strengthening HEV testing in boars, controlling environmental pollution, and reducing the mixed feeding of different stages could contribute to reducing HEV infection in pigs in China and the risk of porcine HEV infection in humans.

A between-herd data-driven stochastic model to explore the spatio-temporal spread of hepatitis E virus in the French pig production network

Hepatitis E virus is a zoonotic pathogen for which pigs are recognized as the major reservoir in industrialised countries. A multiscale model was developed to assess the HEV transmission and persistence pattern in the pig production sector through an integrative approach taking into account within-farm dynamics and animal movements based on actual data. Within-farm dynamics included both demographic and epidemiological processes. Direct contact and environmental transmission routes were considered along with the possible co-infection with immunomodulating viruses (IMVs) known to modify HEV infection dynamics. Movements were limited to 3,017 herds forming the largest community on the swine commercial network in France and data from the national pig movement database were used to build the contact matrix. Between-herd transmission was modelled by coupling within-herd and network dynamics using the SimInf package. Different introduction scenarios were tested as well as a decrease in the prevalence of IMV-infected farms. After introduction of a single infected gilt, the model showed that the transmission pathway as well as the prevalence of HEV-infected pigs at slaughter age were affected by the type of the index farm, the health status of the population and the type of the infected farms. These outcomes could help design HEV control strategies at a territorial scale based on the assessment of the farms' and network's risk.

Controlling hepatitis E virus in the pig production sector: Assessment of the technical and behavioural feasibility of on-farm risk mitigation strategies

Hepatitis E virus (HEV) is a zoonotic agent with pigs as the main reservoir in industrialised countries. Recent studies conducted on pig farms, in experimental conditions or through modelling approaches, have led to a better understanding of the spread of HEV on pig farms. The findings have also made it possible to define a set of measures to reduce HEV prevalence and the risk of marketing contaminated products. The objective of this study was to assess the feasibility of a set of HEV control strategies on pig farms. Individual semi-structured interviews were conducted with farmers, veterinarians and farming advisors to collect general data, their level of knowledge of HEV, their opinion on the technical feasibility of certain changes in practices, their perception of the respective responsibilities of the different stakeholders, and their feelings about the importance of the issue, following the framework of the Theory of Planned Behaviour. The interviews made it possible to highlight potential barriers and preferred motivators for the implementation of on-farm risk mitigation strategies. Barriers included lack of knowledge, scientific gaps, perceived inability to control HEV, and low perception of the importance of the issue. Motivators included professional satisfaction, family recognition, and the opportunity to achieve higher quality standards. Three clusters of stakeholders were also identified, with a group of leaders who could help unlock reluctance and disseminate innovations. This type of behavioural approach appeared useful to help risk managers facilitate zoonotic control on pig farms.

Natural viral co-infections in pig herds affect hepatitis E virus (HEV) infection dynamics and increase the risk of contaminated livers at slaughter

Hepatitis E virus (HEV) is a zoonotic pathogen, in particular genotype 3 HEV is mainly transmitted to humans through the consumption of contaminated pork products. This study aimed at describing HEV infection patterns in pig farms and at assessing the impact of immunomodulating co-infections namely Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and Porcine Circovirus Type 2 (PCV2), as well as other individual factors such as piglets' immunity and litters' characteristics on HEV dynamics. A longitudinal follow-up was conducted in three farrow-to-finish farms known to be HEV infected. Overall, 360 piglets were individually monitored from birth to slaughter with regular blood and faecal sampling as well as blood and liver samples collected at slaughterhouse. Virological and serological analyses were performed to detect HEV, PCV2 and PRRSV genome and antibodies. The links between 12 explanatory variables and four outcomes describing HEV dynamics were assessed using cox-proportional hazard models and logistic regression. HEV infection dynamics was found highly variable between farms and in a lower magnitude between batches. HEV positive livers were more likely related to short time-intervals between HEV infection and slaughter time (<40 days, OR = 4.1 [3.7-4.5]). In addition to an influence of piglets' sex and sows' parity, the sequence of co-infections was strongly associated with different HEV dynamics: a PRRSV or PCV2/PRRSV pre- or co-infection was associated with a higher age at HEV shedding (Hazard Ratio = 0.3 [0.2-0.5]), as well as a higher age at HEV seroconversion (HR = 0.5 [0.3-0.9] and HR = 0.4 [0.2-0.7] respectively). A PCV2/PRRSV pre- or co-infection was associated with a longer duration of shedding (HR = 0.5 [0.3-0.8]). Consequently, a PRRSV or PCV2/PRRSV pre- or co-infection was strongly associated with a higher risk of having positive livers at slaughter (OR = 4.1 [1.9-8.9] and OR = 6.5 [3.2-13.2] respectively). In conclusion, co-infections with immunomodulating viruses were found to affect HEV dynamics in the farrow-to-finish pig farms that were followed in this study.

Serological evidence of hepatitis E virus and influenza A virus infection in farmed wild boars in China

Hepatitis E virus (HEV) and influenza A virus (IAV) are two important pathogens which can infect humans and various animals causing public health problems. In this study, the seroprevalence and risk factors associated with HEV and IAV infection in farmed wild boars were investigated in China. A total of 758 serum samples were collected from farmed wild boars between 2015 and 2016, and antibodies against HEV and IAV were examined by enzyme-linked immunosorbent assay (ELISA) using commercially available kits. The overall prevalence of anti-HEV antibodies was 24.54% (186/758, 95% CI 21.48-27.60) in farmed wild boars. There were statistically significant differences in the HEV seroprevalence in farmed wild boars of different ages (<22 days: 8.33%; 22-66 days: 18.89%; >66 days: 26.36%) (P < 0.05) and different genders (50.00% in male and 23.49% in female) (P <  0.01). However, there was no statistically significant difference in the HEV seroprevalence in farmed wild boars of different regions and different years. The overall IAV seroprevalence was 5.80% (44/758, 95% CI 4.14-7.46), and there was no statistically significant difference in the IAV seroprevalence in farmed wild boars of different ages and genders, collected from different regions and different years. Our results indicate that HEV and IAV infections in farmed wild boars may pose a potential risk for human infection. To our knowledge, this is the first report of HEV and IAV seroprevalence in farmed wild boars in China, which provides baseline data for further studies and for control of HEV and IAV infection in farmed wild boars.

Seroprevalence and risk factors associated with hepatitis E virus infections among people and pigs in Tibet, China

Hepatitis E virus (HEV), the causative agent of hepatitis E, is an important public health problem throughout the world. There is little information available on the autochthonous HEV infection in highland inhabitants (Tibet, average elevation >3000m) of China. Therefore, we conducted a cross-sectional survey to determine the sero-prevalence of Hepatitis E and association of different risk factors in local people and pigs in Tibet, China. For this purpose, serum samples were collected from 600 local volunteers and 453 Tibetan pigs from July 2014 to August 2015. All the samples were examined for the presence of anti-HEV IgG antibodies by using enzyme-linked immunosorbent assay (ELISA). While socio-demographic and behavioral characteristics were also obtained through questionnaire. The present survey found a close relationship among the HEV of Tibetan people and pigs. The prevalence of anti-HEV IgG was detected 39.33% (236/600) and 42.38% (192/453) in local people and pigs, respectively. There was a significance association of different age groups, ethnic groups, people having contact with pigs or consuming uncooked meat, and gender of Tibetan pigs. Our findings confirmed the presence of autochthonous HEV among people and pigs in Tibet, China. Therefore, effective measures should be taken to prevent and control HEV infection in Tibet, China.

From the epidemiology of hepatitis E virus (HEV) within the swine reservoir to public health risk mitigation strategies: a comprehensive review

Hepatitis E virus (HEV) is the causative agent of hepatitis E in humans, an emerging zoonosis mainly transmitted via food in developed countries and for which domestic pigs are recognised as the main reservoir. It therefore appears important to understand the features and drivers of HEV infection dynamics on pig farms in order to implement HEV surveillance programmes and to assess and manage public health risks. The authors have reviewed the international scientific literature on the epidemiological characteristics of HEV in swine populations. Although prevalence estimates differed greatly from one study to another, all consistently reported high variability between farms, suggesting the existence of multifactorial conditions related to infection and within-farm transmission of the virus. Longitudinal studies and experimental trials have provided estimates of epidemiological parameters governing the transmission process (e.g. age at infection, transmission parameters, shedding period duration or lag time before the onset of an immune response). Farming practices, passive immunity and co-infection with immunosuppressive agents were identified as the main factors influencing HEV infection dynamics, but further investigations are needed to clarify the different HEV infection patterns observed in pig herds as well as HEV transmission between farms. Relevant surveillance programmes and control measures from farm to fork also have to be fostered to reduce the prevalence of contaminated pork products entering the food chain.

Genetic heterogeneity of swine hepatitis E virus isolates from Yunnan province, China in 2011-2012

Background

Hepatitis E is a disease of major public-health concern mainly in developing countries. Although molecular and sero-epidemiological investigations of HEV have been performed in many provinces in China, the epidemiological data from Yunnan Province are limited and genotypes are not be fully characterized. In this study the prevalence and characteristics of hepatitis E virus (HEV) detected in pigs from Yunnan province, China was evaluated.

Results

A total of 13 out of 187 pig fecal samples collected in 2011 revealed HEV positive results; likewise, 7 out of 69 samples collected in 2012 exhibited positive results. These findings indicated a total prevalence of 7.8% (20/256). Phylogenetic and molecular evolutionary analysis results revealed that nine strains were found in the samples obtained in 2011, in which 87.1% to 99.4% nucleotide sequence identity was shared among these strains; and 77.0% to 81.9%, 52.2% to 53.6%, 77.0% to 88.2% and 77.9% to 96.8% nucleotide sequence identities were shared with strains representing genotypes 1, 2, 3, and 4. Five strains were detected in the samples obtained in 2012, in which 94.2% to 99.3% nucleotide sequence identity was shared among the strains, and 81.0% to 82.5%, 81.8% to 83.2%, 81.0% to 92.7% and 81.0% to 97.8% nucleotide sequence identities were shared with strains representing the genotypes 1, 2, 3, and 4.

Conclusions

Analysis of fourteen detected HEV strains revealed that three of them were subtype 4d, two were subtype 4b; the nine remaining isolated strains were subtype 4 h. These results indicated that the prevalence of HEV in the swine herds of Yunnan was quite high, additional public-health concerns should focus on pork safety.

Electronic supplementary material

The online version of this article (doi:10.1186/1743-422X-11-162) contains supplementary material, which is available to authorized users.

Seroprevalence and molecular detection of hepatitis E virus in Yunnan Province, China

In this study, the prevalence and characteristics of hepatitis E virus (HEV) in pigs and the general population in the Yunnan province, China, were evaluated. Nine hundred sixty sera, 95 liver and 60 feces samples were randomly collected from pig farms and abattoirs, in addition 173 human sera were sampled in the provincial capital city for a serological survey and an RT-nPCR assay. The screening results showed that among 621 samples collected from five pig farms, the HEV-specific IgG positive rate ranged from 73.2% to 83.5%, and the overall seroprevalence was 78.9% (490/621). A further analysis revealed that the seroprevalence increased with age. The positive rate of human serum samples was 39.9% (69/173). HEV RNA was detected in five swine feces, six swine liver and one anti-HEV-IgM-positive human serum sample by RT-nPCR. Sequence and alignment of the 348-nt PCR-amplified products of 12 HEV strains identified nine distinct nucleotide sequences. Phylogenetic and molecular evolutionary analysis revealed that these nine sequences shared 84.2% to 100.0% nucleotide sequence identity with each other, with all isolates belonging to genotype 4 HEV and clustering with other Chinese swine and human HEV sequences determined earlier. This study results suggest that the prevalence of genotype 4 HEV is serious, both in pig herds and in the human population, and authorities should pay more attention to the prevalence of HEV in southwest China.

The serological prevalence and genetic diversity of hepatitis E virus in farmed rabbits in China

We identified and characterized a novel virus, designated rabbit hepatitis E virus (HEV), in rex rabbits farmed in China. Rabbit HEV is genetically related to but distinct from other known mammalian HEVs and avian HEV and may represent a novel genotype. To evaluate the spread and genetic variation of rabbit HEV, a total of 1094 serum samples were collected from various breeds of rabbits across ten counties in China. All sera were screened for the presence of anti-HEV antibody, HEV antigen and viral RNA. A total of 169 samples (15.4%), from nine of the ten counties, were found to be positive for HEV antibody. The seroprevalence was highest in Wuhan, Hunan Province (53.4%, 55/103). Samples positive for HEV antigen were detected in seven counties and the overall prevalence was 3.7% (41/1094). HEV RNA was detected in 22 samples and all but one of these samples was found to be positive for HEV antigen. Sequence analysis of the 304 bp amplicons within open reading frame 2 showed that all HEV isolates in this study clustered with known rabbit HEV strains, in a branch separate from genotypes 1 to 4. The rabbit HEV strains were genetically heterogeneous and divided into divergent groups. Strains from the same geographic region tended to cluster together. These results indicate that rabbit HEVs with considerable genetic diversity are prevalent in farmed rabbits in China. The potential zoonotic risk of rabbit HEV needs to be investigated and evaluated further.