Hepatitis E virus (HEV) it is a single-stranded RNA virus without an envelope, similar, in many respects, to HAV. It is transmitted in the same manner as other hepatitis viruses, causing an acute, but not chronic, condition. The incubation period ranges from two weeks to two months.
The first reports of HEV isolation were published in 1990 and may be the principle one involving hepatitis in the Third World, with some reported cases among travellers returning from Mexico, Asia, India, and Africa. HEV is generally a benign illness, displaying mild symptoms. So far, HEV is not as common as other hepatitis viruses in the US, but widespread everywhere else.
HEV was first isolated in 1983 and was identified as the source responsible for an epidemic in India in 1955, when 29,000 people fell ill in New Delhi. The cause of the outbreak appeared to come from the city’s water supply. Assuming it was HAV, scientists found no antibodies, concluding that a new virus had appeared.
HEV not only infects humans, but also various species of monkeys, rodents, pigs, and chickens. There are at least two strains of HEV called HEV-Burma and HEV-Mexico, as well as some subgroups.
The greatest risk is to pregnant women, with the mortality rate close to 20%. For some reason, the longer a woman is pregnant, the more likely she is to die from acute HEV.
The only others at high risk for infection are those between the ages of fifteen and forty, with symptoms ranging from none at all to liver failure.
Transmission is via the fecal/oral route, and not through blood or blood products. There is no vaccine at present.