Phylogenetic study of viral isolates of swine and human hepatitis E virus

Hepatitis E is an enterically transmitted viral hepatitis caused by an RNA virus, hepatitis E virus (HEV) first described in 1984 (Kane et al., 1984). Infection is endemic in many developing countries where seroprevalence is as high as 25%. Industrialised countries were considered free from this infection and of the few cases that have been reported, almost all related to people who had travelled in endemic areas. However, the seroprevalence in human population in the developed world may be high, considering the low level of clinical disease. In the last few years there have been increasing numbers of reports of patients with hepatitis E who had not travelled to endemic regions (Clemente-Casares et al., 2003; Zanetti et al., 1999). HEV antibodies were detected in several animal species both in developing and developed countries, suggesting that these animals could be infected by HEV or HEVrelated viruses (Meng, 2000). The presence of hepatitis E antibodies and RNA in swine in Nepal was reported in 1995 (Clayson et al., 1995), and in 1997, sequence data were published, indicating that the swine virus was closely related to human HEV (Meng et al., 1997). To date, four different HEV genotypes have been identified in man (I, II, III and IV) and two in animals (III and IV) and a very high degree of RNA and amino acid sequence similarity was noticed between swine and human isolates from the same geographical area (Schlauder et al., 1999; Meng et al,. 2000; Banks et al., 2004), suggesting a possible interspecies transmission. In this paper we report the results of a study where we compare nucleotide sequences of an ORF-2 fragment from swine and human HEV isolates