Hepatitis E is a viral hepatitis (liver inflammation) caused by infection with a virus called hepatitis E virus (HEV). HEV is a positive-sense single-stranded RNA icosahedral virus with a 7.5 kilobase genome. HEV has a fecal-oral transmission route. It is one of five known hepatitis viruses: A, B, C, D, and E. The HEV genome is approximately 7200 bases in length, is a polyadenylated single-strand RNA molecule that contains three discontinuous and partially overlapping open reading frames (ORFs) along with 5' and 3' cis-acting elements, which have important roles in HEV replication and transcription. ORF1 encode a methyltransferase, protease, helicase and replicase, ORF2 encode the capsid protein and ORF3 encodes a protein of undefined function. The hepatitis E virus causes around 20 million infections a year. These result in around three million acute illnesses and 70,000 deaths annually. It is particularly dangerous for pregnant women, who can develop an acute form of the disease that is lethal in 20 per cent of cases. The virus (HEV) is a major cause of illness and of death in the developing world and disproportionate cause of deaths among pregnant women.