Putative Novel Genotype of Avian Hepatitis E Virus, Hungary, 2010

Krisztián Bányai, Ádám György Tóth, Éva Ivanics, Róbert Glávits, Katalin Szentpáli-Gavallér, and Ádám Dán

Author affiliations: Hungarian Academy of Sciences, Budapest, Hungary (K. Bányai); and Veterinary Diagnostic Directorate, Budapest (Á.G. Tóth, É. Ivanics, R. Glávits, K. Szentpáli-Gavallér, Á. Dán)

Abstract

To explore the genetic diversity of avian hepatitis E virus strains, we characterized the near-complete genome of a strain detected in 2010 in Hungary, uncovering moderate genome sequence similarity with reference strains. Public health implications related to consumption of eggs or meat contaminated by avian hepatitis E virus, or to poultry handling, require thorough investigation.

Avian hepatitis E virus (aHEV) is a causative agent of big liver and spleen disease (BLSD) in chickens (1), which manifests itself, as its name indicates, by hepatosplenomegaly. The etiologic association has been demonstrated worldwide, including Australia, North America, Asia, and Europe (2,3). In Hungary, BLSD was observed during the 1980s, but association of the disease with hepatosplenomegaly was not made in Hungary until 2008 (4,5). Ivanics et al. (5) reported outbreaks of aHEV infection and increased deaths of chickens caused by hepatitis and splenitis and reduced egg production in chicken flocks in Hungary. Tissue samples from chickens collected during 2010 were positive for aHEV by reverse transcription PCR (RT-PCR) (6,7). Paired samples indicated seroconversion upon inoculation as measured by serologic assay, strongly suggesting an etiologic association between BLSD and aHEV infection in the affected chicken flocks (5).
The aHEV is characterized by a small, nonenveloped virion and a 6.6-kb, capped, poly-A tailed single-stranded RNA genome. The genome encodes 3 open reading frames (ORFs). ORF1 is a polyprotein encoding putative functional domains of methyltransferase, papain-like cystein protease, helicase, and RNA polymerase. The capsid protein is encoded by ORF2; ORF3 encodes a multifunctional cytoskeleton-associated protein linked to viral morphogenesis and pathogenesis (1).
aHEV is ≈50% similar at the genomic level to mammalian HEV genotypes; recent proposals classify aHEV into a different taxon, possibly a new genus, within Hepeviridae. GenBank now includes 5 full or nearly complete aHEV genome sequences that could be classified into 1 of the 3 recognized aHEV genotypes. These 5 prototype strains with full or nearly complete genome sequences include a genotype 1 strain from Australia, 2 genotype 2 strains from the United States, and 2 genotype 3 strains from Europe and the People’s Republic of China (6,8–10). Additional putative genotypes have been identified through analysis of an ≈130-nt fragment of the helicase domain, suggesting that diversity within aHEV is higher than recognized (11). Our primary objective was the genetic characterization of an aHEV strain from the 2010 outbreak in Hungary to increase understanding of the origin and evolution of these emerging pathogens.