Background and methods: Genotype IV hepatitis E virus (HEV) has been isolated from humans and swine. To study the relationship between the human and swine reservoirs, we estimated their respective viral burden, analyzed the genetic makeup of the virus populations, and assessed the risk of infection associated with swine farming.
Results: In 2 swine-farming districts of eastern China, 9.6% of swine and 0.3% of healthy human subjects excreted HEV in stool, as did 68.8% of patients with confirmed HEV infection. The virus population circulating in humans consisted of genotype I and at least 4 phylogenetically distinct subgroups of genotype IV viruses, 2 of which concurrently circulated among swine. Persons engaged in occupations related to swine farming were found to have a 74% higher risk of infection than those engaged in other occupations, and persons living in communities downstream of the swine farms were found to have a 29% higher risk of infection than persons living in communities upstream.
Conclusions: Genotype IV HEV is freely transmitted between humans and swine. Because the size of the swine population and its viral burden are much larger than those of humans, transmission of the virus most likely is directed from swine to humans. Infection can be acquired through contact with swine and their waste.