Age-related prevalence of hepatitis E virus in pigs and presence of the virus in slurry stores in the UK

Hepatitis E virus (HEV) is a common cause of acute hepatitis (HE) in developing countries, where the infection is normally waterborne and can occur as epidemics. Domestically acquired HE cases have been reported sporadically also in industrialized countries, including the UK. HEV was first detected in pigs in 1997; since then swine strains have been described worldwide. Swine and humans isolates of the same geographic area are often genetically related, suggesting that swine can represent a reservoir of the infection and that zoonotic transmission of HEV can play a relevant role in industrialized countries. The aim of this study was to investigate the presence and prevalence of HEV infection in pigs at different production stages and in slurry lagoons, and to characterize selected strains. Ten pig farms were visited in Yorkshire and Humberside area of the UK. On each farm five faecal samples were collected from each of the following stages of production: 3-5 weeks, 10-12 weeks, 22-24 weeks and adult sows. In addition a slurry sample was collected from each farm. All samples were tested for HEV RNA using a nested RT-PCR protocol. PCR products from selected positive samples were subsequently purified and sequenced. Sequences were assembled using SeqMan (DNASTAR) and aligned with other swine and human sequence data available in GenBank (www.ncbi.nlm.nih.gov/) using CLUSTALX (version 1.81). Phylogenetic analysis was performed with PHYLIP (version 3.67) using DNADIST and NEIGHBOR. The dendrogram was visualised in Treeview (version 1.6.6). At least one sample from each of the farms tested was positive to HEV, indicating a prevalence of virus excretion of 100% at the herd level. Between herd prevalence varied from 5% to 35% and the mean prevalence of excretion in the 10 herds at the pig level was 21.5%. There was a significant difference in the prevalence of excretion across the difference stages of production; the mean prevalence of excretion within the 3-5 week, 10-12 week, 22-24 week and adult production stages were 26.0, 44.0, 7.9 and 6.0 % respectively. Two of nine (22.2%) slurry lagoons had detectable HEV RNA. Phylogenetic analysis of the sequence data indicated the HEV strains were of genotype 3 and confirmed the close relationship between these viruses and those detected in other pigs and humans in the UK. The findings suggest a high prevalence of HEV in pig herds in Yorkshire and Humberside and complements reports from other countries that growing pigs of 10-12 weeks of age represent the peak of viral excretion, but that excretion amongst adult pigs is not uncommon. Although the infectivity of the HEV detected in the slurry lagoons samples was not determined, this represents useful baseline data in terms of potential transmission sources of HEV to pigs and humans in the UK.