Infection is caused by hepatitis E virus (HEV), a single-stranded, RNA virus belonging to the Hepeviridae family.
HEV is transmitted primarily by the fecal-oral route. In regions with poor sanitation and limited access to safe drinking water, epidemics and interepidemic occurrences of hepatitis E are largely waterborne. Transmission to fetuses and neonates by women infected during pregnancy is common. In Japan, sporadic disease can be zoonotic and foodborne, associated with eating meat and offal (including liver) of deer, boars, and pigs. In France, disease can be acquired from eating figatellu, a sausage delicacy prepared from raw pig liver. Sporadic disease is also observed in other temperate countries, including the United States, but its cause is generally unknown. Shellfish can transmit HEV. Disease from blood transfusion has been reported, although rare.
Waterborne outbreaks (often large, involving hundreds to thousands of people) have occurred in South and Central Asia, tropical East Asia, Africa, and Central America (Map 3-06). Clinical attack rates are highest in young adults aged 15–49 years. In outbreak-prone areas, interepidemic disease is sporadically encountered. In these areas, pregnant women—whether infected sporadically or during an epidemic—are at risk of progressing to liver failure and death after infection. Miscarriages and neonatal deaths also commonly occur as a result of HEV infection.
Sporadic disease also occurs in regions that are not prone to outbreaks, such as the Middle East, temperate East Asia (including China), North and South America, and Europe. Symptomatic disease is observed most frequently in adults aged >50 years. Primary infection acquired by people who are immunosuppressed, particularly solid-organ transplant recipients, may progress to chronic infection.
People living in the United States are at risk of HEV infection when they travel to areas where epidemics have occurred. When traveling in Japan and Europe, eating raw or inadequately cooked venison, boar meat, pig liver, or food products derived from these, is a risk factor for infection.
Map 3-06. Distribution of hepatitis E virus infection, 2012
The incubation period is 2–9 weeks (mean 6 weeks). Signs and symptoms of disease during primary infection include jaundice, fever, loss of appetite, abdominal pain, and lethargy. Acute hepatitis E is frequently self-limited. Pregnant women (particularly those infected during the second or third trimester) may present with or progress to liver failure, and the fetus is at risk for spontaneous abortion and premature delivery. People with preexisting chronic liver disease may undergo further hepatic decompensation when infected with HEV. Recipients of organ transplants may have no symptoms when infected by HEV but can occasionally develop neurologic deficits.
The diagnosis of acute hepatitis E is established by detecting anti-HEV IgM and IgG in serum. Detecting HEV RNA in serum or stools further confirms the serologic diagnosis but is seldom required. Longer-term, serial detection of HEV RNA in serum or stools, regardless of the HEV antibody serostatus, suggests chronic HEV infection. No diagnostic test has been approved by the Food and Drug Administration for use in the United States.
Treatment is supportive.
No vaccine is available, nor are drugs for preventing infection. Travelers should avoid drinking unboiled or unchlorinated water and beverages that contain unboiled water or ice. Travelers should eat only thoroughly cooked food, including seafood, meat, offal, and products derived from these (see Chapter 2, Food & Water Precautions).