Avian HEV is a non-enveloped positive single stranded RNA virus with a genome size of approximate 6.6Kb excluding the 3´ poly(A) tail. The genome organization of all HEV species is similar, with slight differences in the total length and position of the open reading frames (ORF) 1-3. Similar to mammalian HEV, the genome is mainly organized in 3 ORFs, with non-coding regions of 24 and about 130 nt at the 5'- and 3'-end, excluding a poly(A) tail, respectively. ORF1 is located at 5'-end and encodes a polyprotein containing methyltransferase, papain-like cysteine protease, helicase and RNA-dependent RNA polymerase. It overlaps neither with ORF2 nor ORF3 and includes a hypervariable region of around 50 amino acids in length. Following the stop codon of ORF1, there is a short non-coding region, which may play an important role in viral replication. ORF3, which partially overlaps with ORF2, encodes a small phosphoprotein. ORF1 and ORF3 encode non-structural proteins which play a very important role for the replication of the virus. ORF2 is located at the 3'-end of the genome and encodes the capsid protein with a length of 606 amino acids.