Hepatitis E virus is a, non enveloped positive sense single stranded RNA virus, classified in the Family Hepatitis E virus like viruses, genus hepevirus. The HEV genome contains 3 open reading frames of which ORF2 encodes the capsid of the virus. HEV viruses are divided in 4 genotypes, which have a distinct geographical distribution. HEV infects humans, and HEV antibodies have been found in a number of domestic and wild animal species.
Electron microscopy presentation of Hepatitis E virus
Hepatitis E in humans
Clinical HEV infection in humans often presents as a short flu-like illness with fever, anorexia and nausea. Acute hepatitis may occur with jaundice, abdominal pain and elevated liver enzymes and can turn into chronic disease. Mortality rates in people are generally under 0.5%, but may exceed 20% in pregnant women.
Hepatitis E in pigs
Molecular evidence for natural HEV infection in pigs has been reported form endemic and non-endemic countries. Infection strains in pigs are of genotypes 3 and 4 only. In pigs HEV causes a hepatitis but infections seem to mainly run a subclinical course. It is unknown if HEV in pigs affects growth rate or immunity. HEV genotype III viruses have been accepted to have a clear zoonotic potential.
Growing of HEV in cell culture has been very difficult. The establishment of cell culture propagation system for HEV would be an important break through in HEV research. Laboratory diagnosis is performed using antibody detection methods or molecular virus detection methods.
HEV is endemic, worldwide in pig populations and humans. Major mode of transmission is faeco-oral. Person to person spread seems to be of minor importance. Within pig herds there is a rapid pig to pig spread. This is assumed to be mainly faeco-oral but aerosol transmission can not be excluded.
In developed countries, the number of infections in humans is estimated to be 1 per 300000 per year. Much higher numbers are reached in endemic regions in Asia. In developing countries HEV has been associated with large outbreaks of acute hepatitis. Prevalence of HEV in pig farms may be up to 100% in endemic regions. The increasing prevalence of genotype III HEV in pigs in developed countries and the associated zoonotic threat from pig reservoirs to humans has become a major public health concern.
Foodborne HEV genotype 3 infections in humans have been reported from Japan after eating undercooked deer meat and boar meat. Pork production livers may contain infectious HEV but direct associations of HEV infection with pork consumption have not been reported to date.
Prevention and control
For effective prevention and control there is a need for more sensitive and specific HEV assays for detection of HEV antibodies as well as HEV virus (see diagnosis). High health pig farms seem to have a better chance to stay free of the infection. Therefore hygienic measures taken on a farm level may result in a HEV free status. Hygienic measurements together with HEV testing to monitor the effects may lead to a reduction of HEV prevalences. The development of a vaccine for humans could be an important contribution to HEV control in outbreak situations. A HEV (DIVA) vaccine for pigs to be used for eradication purposes could also help to reduce the threat to human health.