Avian HEV (aHEV) belongs to genus Orthohepevirus, which is
placed in family Hepeviridae as a separate species Orthohepevirus
B. The genome of aHEV comprises of single strand positive
sense RNA which 6.6 kb long and is 600 bp shorter than those
of swine and human HEV genotypes. The shorter portion of
aHEV genome compared to the mammalian HEV (mHEV) falls
in ORF1 between methyltransferase (MeT) and helicase (Hel).
Like other genotypes, it also consists of three open reading
frames (ORFs) which are; ORF1, ORF2 and ORF3. The similarity
of aHEV on the basis of capsid protein amino acids sequence is
above 98 % among its genotypes (1-4), but it is 48-49 % in case
of capsid proteins of other genotypes of HEV including human
and swine HEV. So far, four different genotypes of aHEV, isolated
from chickens, have been reported and interestingly all
four genotypes represent single serotype which may encourage
the development of single vaccine for all four genotype.