Adaptation of genotype 3 hepatitis E virus in Eastern China and inverse correlation with genotype 4 hepatitis E virus

We studied the distribution and development of hepatitis E virus (HEV) genotypes 3 and 4 in pig farms located within the Shanghai metropolitan area. A total of 1,487 swine fecal samples were collected from 39 pig farms during 2009-2010. The average incidence rates for genotype 3 and genotype 4 HEV were 10.6 and 9.3%, respectively. The frequencies of genotype 3 and genotype 4 HEV among the farms were inversely related (r = -0.7423), suggesting that the two genotypes competed within the environmental niche provided by the porcine host. In addition, all of the farms tested positive for both genotype 3 and genotype 4 HEV, indicating that the former is becoming more prevalent in the Shanghai area. The overall HEV incidence rate during 2009-2010 was 20%, which supports the existence of homeostasis within the porcine HEV reservoir.