High Prevalence and Genetic Heterogeneity of Genotype 3 Hepatitis E Virus in Wild Boar in Umbria, Central Italy

Abstract

Hepatitis E virus (HEV) is an important human pathogen and, in developed countries, most human infections are due to a zoonotic cycle, mainly maintained by domestic and wild suids. In European countries several genotype 3 strains have been found to circulate in human population and animal reservoirs, with human infections being related mostly to pork or wild boar meat consumption. In this study, we surveyed HEV circulation in wild boar in Umbria (Italy) during the 2021–2022 hunting seasons, using a stratified sampling. Liver samples were tested for HEV presence by real-time RT-qPCR. Positive samples were characterized by nested RT-PCR followed by sequencing of partial region of the capsid gene. Overall, 78 out of 179 wild boar liver samples tested positive to HEV (43.6%), with viral load ranging between 1.47 and 7.35 log genome copies/g (median 3.20 log). Variations, although not statistically significant, were observed considering geographical, age, weight, and gender factors, in terms of either prevalence or viral load. In particular, in animals younger than 1 year of age, the viral load was 2 log higher (median viral load of 5.50 log genome copies/g of liver tissue) than in older age groups. Sequence analysis characterized the 41 obtained sequences into genotype 3 subtype 3c (n = 4), 3f (n = 11), and 3e (n = 1), while 13 sequences clustered with two genotype 3 genomes (GenBank MF959764 and MK390971) still unassigned to subtypes. Additional, 12 sequences did not cluster with any known subtype or unassigned genome and on phylogenetic analysis segregated into two distinct groups of eight and four sequences, respectively. Interestingly, some wild boar sequences of subtype 3f were intermingled with sequences of HEV strains previously identified in human patients in Central Italy. Sharing of molecular data for HEV in animals is pivotal to decipher the intricate ecology of HEV.