Restricted enzooticity of hepatitis E virus genotypes 1 to 4 in the United States

Abstract

Hepatitis E is recognized as a zoonosis, and swine are known reservoirs, but how broadly enzootic its causative agent, hepatitis E virus (HEV), is remains controversial. To determine the prevalence of HEV infection in animals, a serological assay with capability to detect anti-HEV-antibody across a wide variety of animal species was devised. Recombinant antigens comprising truncated capsid proteins generated from HEV-subgenomic constructs that represent all four viral genotypes were used to capture anti-HEV in the test sample and as an analyte reporter. To facilitate development and validation of the assay, serum samples were assembled from blood donors (n = 372), acute hepatitis E patients (n = 94), five laboratory animals (rhesus monkey, pig, New Zealand rabbit, Wistar rat, and BALB/c mouse) immunized with HEV antigens, and four pigs experimentally infected with HEV. The assay was then applied to 4,936 sera collected from 35 genera of animals that were wild, feral, domesticated, or otherwise held captive in the United States. Test positivity was determined in 457 samples (9.3%). These originated from: bison (3/65, 4.6%), cattle (174/1,156, 15%), dogs (2/212, 0.9%), Norway rats (2/318, 0.6%), farmed swine (267/648, 41.2%), and feral swine (9/306, 2.9%). Only the porcine samples yielded the highest reactivities. HEV RNA was amplified from one farmed pig and two feral pigs and characterized by nucleotide sequencing to belong to genotype 3. HEV infected farmed swine primarily, and the role of other animals as reservoirs of its zoonotic spread appears to be limited.

Fig. 1.

Comparison of DASA and DS EIA reactivities. (A) Distribution of signal/cutoff OD values. Numerals atop bars denote sample numbers. (B) Correlation between signal cutoff values. (Inset: 2 × 2 table showing concordance of detection).

Fig. 2.

Anti-HEV reactivities in swine seroconversion panels. Symbols: •, DASA; ▴, 55-kDa-EIA. ID16, uninoculated control; ID25, ID34, and ID1238, inoculated with human genotype 3, human genotype 4, and swine genotype 3 HEV, respectively.

Fig. 3.

Distribution of DASA reactivities in five animal species. Horizontal line indicates the s/co of 4.

Fig. 4.

Phylogenetic trees comparing sequence similarities of USfsw-1 (GenBank accession numbers JN 701455 and JN 701453), USfsw-2 (GenBank accession numbers JN 701456 and JN 701454), and USsw-21 (GenBank accession number JN 701457) to representative GenBank sequences. (A) ORF1; (B) ORF2.