A novel genotype of avian hepatitis E virus identified in chickens and common pheasants (Phasianus colchicus), extending its host range.

In 2019, outbreaks of hepatitis-splenomegaly syndrome (HSS) were observed in six commercial layer chicken flocks, belonging to three different Polish farms, and characterized by increased mortality, hemorrhagic hepatitis with attached blood clots on the liver surface, and splenomegaly. Diseased flocks were initially investigated for the presence of avian hepatitis E virus (aHEV) - the etiological agent of HSS - by conventional reverse transcriptase polymerase chain reaction, which revealed aHEV sequences clustering separately from all known aHEV genotypes. Additionally, an aHEV genome was identified for the first time in common pheasants, from a flock in France, using Next Generation Sequencing. This genome clustered together with the Polish aHEVs here investigated. Complete genome aHEV sequences from the HSS outbreaks confirmed the divergent cluster, with a shared nucleotide sequence identity of 79.6-83.2% with other aHEVs, which we propose to comprise a novel aHEV genotype - genotype 7. Histology and immunohistochemistry investigations in the liver and spleen established an association between aHEV and the observed lesions in the affected birds, consolidating the knowledge on the pathogenesis of aHEV, which is still largely unknown. Thus, the present investigation extends the natural host range and genotypes of aHEV and strengthens knowledge on the pathogenesis of HSS.

Subclinical circulation of avian hepatitis E virus within a multiple-age rearing and broiler breeder farm indicates persistence and vertical transmission of the virus.

In a prospective longitudinal study, a broiler breeder flock and its progeny were monitored for the presence of avian hepatitis E virus (HEV) RNA and antibodies. The flock was part of a multiple-age farm where the presence of avian HEV with clinical signs (increased mortality and decreased egg production) was demonstrated in several previous production cycles. Samples were taken twice at the rearing site and several times at the production site from broiler breeders including cockerels and day-old chicks. The samples were investigated by conventional and real-time reverse transcriptase-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and histological methods. At all time points, samples from the hens were positive for avian HEV RNA. The birds did not show any clinical signs, even though histopathological lesions of non-specific aetiology in the liver and spleen could be demonstrated. A significant increase in the number of positive birds and viral load was seen in week 45, in accordance with an increase in antibody titres. In comparison, cockerels investigated in week 62 tested negative by RT-PCR and ELISA. Avian HEV RNA was also detected in day-old chicks hatched from eggs laid in week 25, indicating vertical transmission. All partial helicase and capsid sequences retrieved within this study clustered together and were identical to previous sequences obtained from the same multiple-age farm. In conclusion, avian HEV persisted on the farm over years and circulated between the rearing and the production sites without causing any clinical signs although high viral loads in the adult hens were observed.