Variability and pathogenicity of hepatitis E virus genotype 3 variants

Abstract

Infection with hepatitis E virus (HEV) can be clinically inapparent or produce symptoms and signs of hepatitis of varying severity and occasional fatality. This variability in clinical outcomes may reflect differences in host susceptibility or the presence of virally encoded determinants of pathogenicity. Analysis of complete genome sequences supports the division of HEV genotype 3 (HEV-3) variants into three major clades: 3ra comprising HEV isolates from rabbits, and 3efg and 3abchij comprising the corresponding named subtypes derived from humans and pigs. Using this framework, we investigated associations between viral genetic variability of HEV-3 in symptomatic and asymptomatic infections by comparing HEV-3 subgenomic sequences previously obtained from blood donors with those from patients presenting with hepatitis in the UK (54 blood donors, 148 hepatitis patients), the Netherlands (38 blood donors, 119 hepatitis patients), France (24 blood donors, 55 hepatitis patients) and Germany (14 blood donors, 36 hepatitis patients). In none of these countries was evidence found for a significant association between virus variants and patient group (P>0.05 Fisher's exact test). Furthermore, within a group of 123 patients in Scotland with clinically apparent HEV infections, we found no evidence for an association between variants of HEV-3 and disease severity or alanine aminotransferase level. The lack of detectable virally encoded determinants of disease outcomes in HEV-3 infection implies a more important role for host factors in its clinical phenotype.

Fig. 1.

Phylogenetic analysis of HEV-3 complete genome sequences (GenBank accession numbers). A neighbour-joining tree of 81 HEV-3 complete genome sequences together with reference sequences of other genotypes was produced using maximum composite likelihood distances. Named subtypes of 3abchij are enclosed by a grey bracket and those of 3efg by a dark bracket. Isolates belonging to clade 3ra are identified by open squares. Bootstrap support (>70 %) is indicated for individual branches.

Fig. 2.

Frequency histogram of nucleotide p distances amongst HEV-3 variants. Pairwise distances amongst the complete genome sequences (from which the HVR had been removed) of the HEV-3 sequences shown in Fig. 1, but excluding the 3ra variants. The distributions of sequence distances within subtype, between subtypes and between clades (3abchij and 3efg) are indicated.

Fig. 3.

Phylogenetic analysis of HEV-3 variants from blood donors and hepatitis patients in England and Wales. HEV-3 ORF2 sequences (280 nt, nt 6041–6320 numbered relative to AF082843) isolated from blood donors (•) and hepatitis patients (○) were compared with reference sequences of named HEV-3 subtypes and 3ra isolates (▪).

Fig. 4.

Phylogenetic analysis of HEV-3 variants from blood donors and hepatitis patients in the Netherlands. ORF2 sequences (304 nt, nt 6018–6321) isolated from blood donors (•) and hepatitis patients (○) were compared with reference sequences of named HEV-3 subtypes and 3ra isolates (▪).

Fig. 5.

Phylogenetic analysis of HEV-3 variants from blood donor and hepatitis patients in (a) Germany (ORF1 nt 107–348) and (b) France (ORF2 nt 5996–6342): blood donors (•) and hepatitis patients (○) together with named subtypes and 3ra isolates (▪). Branches with >70 % bootstrap support are indicated.