Hepatitis E in southern Vietnam: Seroepidemiology in humans and molecular epidemiology in pigs

Abstract

Viral pathogens account for a significant proportion of the burden of emerging infectious diseases in humans. The Wellcome Trust-Vietnamese Initiative on Zoonotic Infections (WT-VIZIONS) is aiming to understand the circulation of viral zoonotic pathogens in animals that pose a potential risk to human health. Evidence suggests that human exposure and infections with hepatitis E virus (HEV) genotypes (GT) 3 and 4 results from zoonotic transmission. Hypothesising that HEV GT3 and GT4 are circulating in the Vietnamese pig population and can be transmitted to humans, we aimed to estimate the seroprevalence of HEV exposure in a population of farmers and the general population. We additionally performed sequence analysis of HEV in pig populations in the same region to address knowledge gaps regarding HEV circulation and to evaluate if pigs were a potential source of HEV exposure. We found a high prevalence of HEV GT3 viral RNA in pigs (19.1% in faecal samples and 8.2% in rectal swabs) and a high HEV seroprevalence in pig farmers (16.0%) and a hospital-attending population (31.7%) in southern Vietnam. The hospital population was recruited as a general-population proxy even though this particular population subgroup may introduce bias. The detection of HEV RNA in pigs indicates that HEV may be a zoonotic disease risk in this location, although a larger sample size is required to infer an association between HEV positivity in pigs and seroprevalence in humans.

Keywords: Vietnam; hepatitis E virus; human; pigs; prevalence; seroprevalence; zoonosis.

Figure 1

Study design diagram and results summary

Figure 2

The phylogenetic relationships of hepatitis E virus sampled from Vietnamese pigs. Maximum-likelihood phylogeny constructed using RNA sequences from 64 Vietnamese pigs, and 37 reference sequences from the conserved region within the HEV ORF2 region (300 bp) from all four genotypes accessed from GenBank. Scale bar indicates the number of substitutions per site. Bootstrap support values are shown for nodes with ≥70% bootstrap support. The tree is mid-point rooted for clarity. Sequences from Vietnamese pigs are labelled in red. (Abbreviations: sw; swine, wb; wild boar; h; human). [Colour figure can be viewed at wileyonlinelibrary.com]

Figure 3

Seroprevalence in both general population and framers cohort groups analysed in this study. The graphs represent the total seroprevalence observed in the general population (left panel) and in the farmer cohort (right panel) stratified by age. Y-axis shows the seroprevalence percentage of people anti-HEV IgG positive, while the X-axis indicates the age groups; individuals were grouped into 3-year-age bands for maximum informativeness and clarity. The red line shows the inferred seroprevalence curve, and the pink shaded area shows the 95% confidence band. The grey dots show the seroprevalence for each 3-year-age group, and the size of the dot is proportional to the sample size. [Colour figure can be viewed at wileyonlinelibrary.com]