Cross-species transmission is likely to be dependent upon genotype:
most swine isolates are genotype 3 or 4 whereas the majority of human
infections are of genotype 1 and 2. Pigs are not alone in being susceptible
to HEV, with various reports of rats, lambs, dogs, cats, goats, cattle
and chickens also being susceptible. Chicken isolates are only 62%
identical in genome sequence with human and swine isolates leading
to the suggestion that HEV in poultry may represent a distinct genus.29
As with swine HEV, serological studies have shown that approximately
70% of poultry flocks in the United States are infected with HEV.30
There is no evidence of transmission from poultry to humans, but of
course this could change, especially since work so far has shown isolates
are genetically heterogeneous and thus adaptation could readily
occur.