Hepatitis E

How the Hepatitis E virus (HEV) is transmitted and is it a serious health problem?

Abstract

Hepatitis E is a small, non-enveloped RNA virus which is transmitted mainly by the faecal-oral route. As the organisation of HEV's genome structure resembled that of Caliciviridae, it was once thought to be a member of this family. However recent advances in clinical and laboratory research have shown that its genomic organisation closely resembles that of the rubella virus and plant furoviruses than that of Caliciviruses. There is an increasing concern that HEV acts as a possible zoonotic agent between certain animals and humans. There is also evidence that humans can be infected with divergent HEV strains which shows the possibility of the emergence and evolution of new HEV strains.

Introduction

As mentioned in the abstract, HEV virions are small, non-enveloped 32-34nm diameter particle with isosahedral symmetry. The viral genome is approximately 7.5kb in length and is a single stranded, positive-sense, polyadenylated RNA molecule that contains short 5' and 3' non-coding regions of 27 and 68 nucleotides respectively. It also contains 3 open reading frames (ORF's). Aggarwal, R and Krawczynski, K. Journal of Gastro and Hepat Vol 15 2000

Viral Hepatitis E: http://www.meddean.luc.edu/lumen/MedEd/orfpath/virhepe.htm

There are two distinct geographic strains of the disease, Burmese (or Asian) and Mexican. Even though the two possess genomic variability, they share at least one major cross reactive epitope. New isolates of HEV have emerged in certain region of the world such as in the US where it was designated HEV US-1.

The disease occurs mainly in the developing world, affecting young adults predominantly (age group 15-40). HEV has a high fatality rate amongst pregnant women 15-20%. Pregnant women in their third trimester seem to suffer from the worst scenarios of hepatic failure and mortality rates can rise to 25%. The frequency of abortion, neonatal

Death and still birth increase in women infected with HEV. The severity of the virus amongst pregnant women is evident with an outbreak in Kashmir which showed approximately 20% of infected pregnant women suffered hepatic failure compared with 2.8% of infected men. Khuroo MS, Teli MR: AM J Med. 1981

The symptoms of Hepatitis E are flu-like symptoms, fatigue, nausea, diarrhea, jaundice, yellow eyes and yellow skin. There is a 1-2% chance of the individual developing sudden and severe liver damage which potentially could lead to a liver transplant being needed.

Time course of hepatitis E virus infection: Shahid Jameel; http://www-ermm.cbcu.cam.ac.uk/99001295h.htm

No effective treatment exists and the only cure is prevention. No commercial vaccines are available throughout the world. There are four major genotypes that have been identified and only one serotype of HEV is recognized. This shows a broad protective vaccine is possible in the future.

Transmission

The faecal-oral route is the primary mode of transmission of epidemic HEV infection.

The majority of epidemic cases have been shown to be related to consumption of common contaminated water. Many of the cases follow heavy rainfall and subsequent flooding. The significant majority of cases take place in developing countries and the poor standard of hygiene coupled with poor sewage systems lead to the spread of epidemic cases. Epidemic cases may arise during hot summer months when reduction in water levels may contribute to an increased risk of infection.

Person to person transmission of HEV appears to be distinctly uncommon. Secondary attack rates among household members are only 0.7-2.2%; in contrast, 50-75% of susceptible household contacts of hepatitis A cases are known to be infected. Multiple familial cases occur not due to exposure to each other but to contaminated water. It should not be disregarded that food and fomites, even human to human spread may be plausible. An example of nosocomial spread from a patient in South Africa to three health care work workers is a recent case. Aggarwal, R and Krawczynski, K. Journal of Gastro and Hepat Vol 15 2000

Transmission of HEV from mother to child is also known to occur. There are numerous studies which show that around 75% of babies born to mothers who had uncomplicated hepatitis or hepatic failures from HEV infection were born with HEV infection. Currently there is no solid evidence for the transmission of HEV via sexual intercourse however in Italy, a report showed 20% of homosexual men had anti HEV antibodies as compared with only 3% of IV drug users-this suggests the faecal-oral transmission of HEV. There is evidence for the transmission of HEV by transfusion of blood or blood products.

An environmental reservoir of the disease must exist in regions where epidemics break out. It has been shown that HEV is an adaptable virus which withstands high concentrations of salt, freeze thawing and pelting. Another potential reservoir for HEV may be in the form of serial transmission among particular susceptible individuals. The possibility of zoonotic spread of the disease also exists, since several animal species (pigs, cows, sheep's and goats) are susceptible to the virus. The HEV US-1 isolate of the virus and swine HEV have been shown to be phylogenetically related and to possess cross-species infectivity. A reported incidence was that of a man contracting the HEV US-1 strain even though the patient had no history of travel to disease endemic regions-strongly suggesting zoonotic transmission.

HEV-is it a serious health issue?

http://virology-online.com/viruses/HepatitisE.htm

HEV accounts for more than 50% of acute viral hepatitis amongst young adults in developing nations. The rate of fatal fulminant hepatitis amongst non pregnant patients is at 1-3% whereas the fatality rate amongst infected pregnant women can be as high as 25%. Serkan Oncu et al, MedSciMont 2006. This demonstrates the severity of the issue at hand. Developing nations generally have a high level of pregnancy which subsequently means a high birth rate. The number of cases will continue to persist and this reiterates