Hepatitis E

Clinical Description

Identification

Clinical course similar to that of hepatitis A; no evidence of a chronic form. The case-fatality rate is similar to that of hepatitis A except in pregnant women, where it may reach 20% among those infected during the third trimester of pregnancy. Epidemic and sporadic cases have been described.

Infectious Agent

The hepatitis E virus (HEV), the only known Hepevirus, is a spherical, non-enveloped, single-stranded RNA virus approximately 32 to 34 nanometers in diameter, classified in the Hepeviridae family. HEV is comprised of at least five genotypes.


Diagnosis

Diagnosis depends on clinical and epidemiological features and exclusion of other causes of hepatitis, especially hepatitis A, by serological means. Acute hepatitis E is diagnosed in the presence of IgM anti-HEV. HEV RNA can be detected by PCR in acute phase feces in approximately 50% of cases. Western blot assays to detect anti-HEV IgM and IgG in serum can be used to confirm the results of EIA tests, along with PCR tests for the detection of HEV RNA in serum and feces, immunofluorescent antibody blocking assays to detect antibody to HEV antigen in serum and liver, and immune electron microscopy to visualize viral particles in feces.


Epidemiology

Mode of Transmission

Primarily by the fecal-oral route; fecally contaminated drinking-water is the most commonly documented vehicle of transmission. Person-to-person transmission probably also occurs through the fecal-oral route, although secondary household cases are uncommon during outbreaks. Recent studies suggest that hepatitis E may in fact be a zoonotic infection with coincident areas of high human infection.

Incubation Period

The range is 15 to 64 days; the mean incubation period has varied from 26 to 42 days in various epidemics.

Period of Communicability

Not known. HEV has been detected in stools 14 days after the onset of jaundice and approximately 4 weeks after oral ingestion of contaminated food or water, where it persists for about 2 weeks.

Reservoir

Humans are natural hosts for HEV; some non-human primates (e.g. chimpanzees, cynomolgus monkeys, rhesus monkeys, pigtail monkeys, owl monkeys, tamarins and African green monkeys) are reported as susceptible to infection with HEV. Cows, sheep and goats, particularly the first two, have high prevalences of anti-HEV in some populations. Thus, they may be sources of zoonotic infections of humans.

Susceptibility

Unknown. Over 50% of HEV infections may be anicteric; the expression of icterus appears to increase with increasing age. Women in the third trimester of pregnancy are especially susceptible to fulminant disease. The occurrence of major epidemics among young adults in regions where other enteric viruses are highly endemic and most of the population acquires infection in infancy remains unexplained.

Occurrence

HEV is the major causal agent of enterically transmitted non-A, non-B hepatitis worldwide. In recent years, serological tests for both IgM and IgG anti-HEV have allowed a comprehensive epidemiological survey of the distribution of HEV: the prevalence of HEV antibodies in suspected or documented endemic regions was much lower than expected (3%–26%), and was higher than anticipated (1–3%) in non-endemic regions such as north America. Outbreaks of hepatitis E and sporadic cases occur over a wide geographic area, primarily in countries with inadequate environmental sanitation. HEV infections account for 50% of acute sporadic hepatitis in some highly endemic areas, and hepatitis E virus is the single most important cause of acute clinical hepatitis among adults throughout central and southeast Asia, and the second most important cause, behind hepatitis B virus, in the Middle East and north Africa. The highest rates of clinically evident disease occur in young to middle-aged adults; lower disease rates in younger age groups may be the result of anicteric and/or sub-clinical HEV infection. In most industrialized countries, hepatitis E cases have been documented almost only among travelers returning from HEV endemic areas. Outbreaks often occur as waterborne epidemics, but sporadic cases and epidemics not clearly related to water have been reported. Outbreaks have also been reported from: Algeria; Bangladesh; Chad; China; Côte d'Ivoire; Egypt; Ethiopia; Greece; India; Indonesia; the Islamic Republic of Iran; Jordan; the Libyan Arab Jamahiryia; Mexico; Myanmar; Nepal; Nigeria; Pakistan; southern areas of Russia; Somalia; eastern Sudan; and The Gambia. A large waterborne outbreak (3 682 cases) occurred in 1993 in Uttar Pradesh, India.


Prevention and Control

1)    Preventive measures:

Provide educational programs to stress sanitary disposal of feces and careful hand-washing after defecation and before handling food; follow basic measures to prevent fecal-oral transmission, as listed under Typhoid fever page. Administration of immune serum globulin from endemic areas has not decreased infection rates during epidemics in India; encouraging advances have occurred in HEV vaccine development.

2)    Control of patient, contacts and the immediate environment:

a)    Report to local health authority, Isolation and Concurrent disinfection: See Hepatitis A page.

b)    Quarantine: Not applicable.

c)    Immunization of contacts: No products are available to prevent hepatitis E. IG prepared from plasma collected in non- and high-HEV endemic areas was not effective in preventing clinical disease during hepatitis E outbreaks. Prototype hepatitis E vaccines have been shown to prevent significant illness, but despite these successes in field trials, they are not yet marketed.

d)    Investigation of contacts and source of infection: Same as for hepatitis A.

e)    Specific treatment: None.

3)    Epidemic measures:

Determine mode of transmission through epidemiological investigation; investigate water supply and identify populations at increased risk of infection; make special efforts to improve sanitary and hygienic practices in order to eliminate fecal contamination of foods and water.

4)    Disaster implications:

A potential problem where there is mass crowding and inadequate sanitation and water supplies. If cases occur, increased effort should be exerted to improve sanitation and the safety of water supplies.

5)    International measures:

None.

 

Source: Heymann (Ed.). (2008). Control of Communicable Diseases Manual, 19th edition. Washington, DC: American Public Health Association.

Common Disease Taxonomy: