Molecular investigation of hepatitis E virus infection in patients with acute hepatitis in Kathmandu, Nepal.

One hundred fifty-four consecutive patients with sporadic acute hepatitis, who were seen at a city hospital in the Kathmandu valley of Nepal in 1997, were studied. IgM antibodies to hepatitis A virus were detected in four patients (3%), IgM antibodies to hepatitis B core in four patients (3%), hepatitis B surface antigen in 20 (13%), and hepatitis C virus RNA in four patients (3%). IgM antibodies to hepatitis E virus (HEV) (anti-HEV IgM) and HEV RNA were detected in 77 (50%) and 48 (31%), respectively. Consequently, 86 patients (56%) including nine HEV-viremic patients without anti-HEV IgM, were diagnosed with hepatitis E. The cause of hepatitis was not known in 53 patients (34%). All 48 HEV RNA-positive samples were genotyped as 1, and subtyped further as 1a in 17 (35%), 1c in 29 (60%), and mixed infection of 1a and 1c in 2 (4%). A seasonal difference in the prevalence of HEV subtypes was recognized. Before the rainy season (January to July), both 1a and 1c isolates were found: the intrasubtypic difference was up to 9.0% and 1.7%, respectively, in the 412-nucleotide sequence of open reading frame 2. During the rainy season (August), only 1c isolates (n = 17) with 99.5-100% identity were found; 13 of 17 isolates had the same sequence, being identical to the 3 isolates that emerged at the end of July. These results suggest that a particular HEV 1c strain spread widely during the rainy season and was implicated in a small epidemic in the Kathmandu valley in August 1997.