Epidemiology and pathogenesis

HEV is the most common cause of acute hepatitis and jaundice in the world, although it is uncommon in the developed world. It has been estimated to cause at least 3.3 million cases of hepatitis per year and result in approximately 70,000 deaths.[4] In endemic areas, seroprevalence rates of HEV infection range between 30-80%, usually due to genotypes 1 and 2.[5] In these areas HEV infection occurs both sporadically and in epidemics and is predominantly spread by faecally-contaminated water while person-to-person spread is uncommon. HEV can also be transmitted by blood transfusion, particularly in endemic areas.[6][7] The highest incidence of HEV infection occurs in Asia, Africa, the Middle East, and Central America. HEV is the second most common cause of sporadic hepatitis in North Africa and the Middle East.[8] High attack rates are found in adults between 15 and 40 years of age.[9] Secondary attack rates from person-to-person transmission in susceptible households are uncommon but have been documented.[10]

Seroprevalence rates of HEV infection in resource-rich areas of the world, such as Europe and the United States of America (USA), are lower than in countries where HEV infection is endemic, with the USA reporting rates of 21%.[11] However, this rate is surprisingly high and suggests a high rate of subclinical HEV infection. In these regions, cases are sporadic and have been predominantly described in people who have travelled to areas of the world where HEV infection is endemic.[12] However, sporadic cases that were not associated with travel have also been reported.[13] HEV can infect pigs, suggesting that some cases of human transmission may be due to transmission across species.[13][14] This assumption is further supported by the identification of HEV RNA in a high percentage of pig liver and sausage in commercial settings.[15] Zoonotic transmission is also supported by the observation of high seroprevalence rate for HEV infection among people with occupational contact with animals.[16] There is also evidence that infection can be associated with exposure to other animals such as game[17] as well as shellfish.[18]

There is also some limited information that vertical transmission of HEV from mothers with HEV infection to their infants can occur. In one report, eight babies were born to mothers with HEV in the third trimester of pregnancy. Six infants had clinical, serological, or virological evidence of HEV infection. Two infants died within 24 hours of birth, one of whom had massive hepatic necrosis at autopsy.[11] This finding suggests that HEV infection can be transmitted from mother to newborn with significant perinatal morbidity and mortality.