Reduced prevalence of genotype 3 HEV in Shanghai pig farms and hypothetical homeostasis of porcine HEV reservoir

A total of 493 fecal samples collected from local Shanghai pig farms were examined for Hepatitis E virus (HEV) after the introduction of stricter sanitary measures following outbreaks of a high fever-associated pig disease during 2006 and 2007. Our investigation revealed that, while the overall occurrence of HEV RNA positives decreased by only 3.7%, the incidence of HEV genotype 4 increased from 9.8% to 20.6% whereas the incidence of HEV genotype 3 decreased from 16.2% to 1.6%. As well as demonstrating that HEV genotype 3 was more sensitive than genotype 4 to the stricter sanitation procedures, our data also suggested that a homeostasis mechanism, whereby the overall incidence of HEV is maintained at a specific population level, might exist in the porcine HEV reservoir. Furthermore, in one case, we encountered the coexistence of HEV genotypes 3 and 4 within the same sample, indicating the possibility of future HEV infections of increased severity and even the occurrence of a HEV pandemic due to genetic recombination and species evolution.