Study of Animal Mixing and the Dynamics of Hepatitis E Virus Infection on a Farrow-to-Finish Pig Farm

Abstract

In Europe, swine are a livestock reservoir for Hepatitis E virus genotype 3 (HEV-3). Consumption of food containing HEV-3 can cause zoonotic human infection, though risk is reduced by heat treatment. Implementing controls that limit infection in slaughter pigs may further reduce foodborne transmission risk but knowledge of infection dynamics on commercial farms is limited. This study addressed this knowledge gap and in particular investigated the influence of group mixing. Faeces were collected from grower (n = 212) and fattener (n = 262) pigs on a farrow-to-finish farm on four occasions. HEV RNA was detected on all occasions, and prevalence was higher in growers (85.8%) than fatteners (26.0%; p < 0.001). HEV-positive samples were also collected from the wider farm environment (n = 67; 64.7% prevalence), indicating potential sources for HEV re-circulation within the herd. Timing of infection in a cohort was also investigated. HEV was absent from all piglet faeces (n = 98) and first detected at weaner stage (25.7% prevalence), but only in groups weaned earlier or comprising pigs from many different litters. Farrowing sow faeces (n = 75) were HEV-negative but antibodies were detected in blood from two sows. Results suggest that multiple factors influence HEV infection dynamics on pig farms, and potential foci for further study into practical control solutions are highlighted.

Keywords: HEV; Hepatitis E virus; farm; pig; swine; within-herd transmission; zoonosis.

Figure 1

(a) Prevalence and 95% confidence intervals of HEV RNA in all faecal samples collected from the pens of grower and fattener pigs during four visits to the study farm. (b) Boxplots of viral load (log₁₀ HEV copy number per gram) in HEV-positive faecal samples taken from the pens of grower and fattener pigs during four visits to the study farm (stars represent outliners). Data do not include samples collected from the study cohort, which are presented separately in Figure 2.

Figure 2

(a) Prevalence and 95% confidence intervals of HEV RNA in all faecal samples and (b) viral load (log₁₀ copy number per gram) in HEV-positive faecal samples taken from a cohort of pigs on a farrow-to-finish farm in England when sampled at 3–4 weeks, 10–11 weeks, 17–18 weeks and 21–22 weeks of age.