A 20 year old male presented with jaundice for the past 2 weeks. His liver function tests revealed serum bilirubin to be 0.9 mg/dL, SGOT/SGPT to be 1240/1450 IU. He was found to be positive for HBsAg and IgM anti-HEV antibodies and negative for 1gM anti HBc. The most likely diagnosis is