|
| Hepatitis C is a viral infection of the liver which had been referred to as
parenterally1 transmitted "non A, non B hepatitis" until identification of the
causative agent in 1989. The discovery and characterization of the hepatitis C
virus (HCV) led to the understanding of its primary role in post-transfusion
hepatitis and its tendency to induce persistent infection.
HCV is a major cause of acute hepatitis and chronic liver disease, including
cirrhosis2 and liver cancer. Globally, an estimated 170 million persons are
chronically infected with HCV and 3 to 4 million persons are newly infected each
year. HCV is spread primarily by direct contact with human blood. The major
causes of HCV infection worldwide are use of unscreened blood transfusions, and
re-use of needles and syringes that have not been adequately sterilized.
No vaccine is currently available to prevent hepatitis C and treatment for
chronic hepatitis C is too costly for most persons in developing countries to
afford. Thus, from a global perspective, the greatest impact on hepatitis C
disease burden will likely be achieved by focusing efforts on reducing the risk
of HCV transmission from nosocomial 3exposures (e.g. blood transfusions, unsafe
injection practices) and high-risk behaviours (e.g. injection drug use).
Pathogen
Hepatitis C virus (HCV) is one of the viruses (A, B, C, D, and E), which
together account for the vast majority of cases of viral hepatitis. It is an
enveloped RNA virus in the flaviviridae family which appears to have a narrow
host range. Humans and chimpanzees are the only known species susceptible to
infection, with both species developing similar disease.
An important feature of the virus is the relative mutability of its genome,
which in turn is probably related to the high propensity (80%) of inducing
chronic infection. HCV is clustered into several distinct genotypes which may be
important in determining the severity of the disease and the response to
treatment.
Clinical features of acute infection
The incubation period of HCV infection before the onset of clinical symptoms
ranges from 15 to 150 days. In acute infections, the most common symptoms are
fatigue and jaundice; however, the majority of cases (between 60% and 70%), even
those that develop chronic infection, are asymptomatic.
Chronic infection and consequences
About 80% of newly infected patients progress to develop chronic infection.
Cirrhosis develops in about 10% to 20% of persons with chronic infection, and
liver cancer develops in 1% to 5% of persons with chronic infection over a
period of 20 to 30 years. Most patients suffering from liver cancer who do not
have hepatitis B virus infection have evidence of HCV infection. The mechanisms
by which HCV infection leads to liver cancer are still unclear. Hepatitis C also
exacerbates the severity of underlying liver disease when it coexists with other
hepatic conditions. In particular, liver disease progresses more rapidly among
persons with alcoholic liver disease and HCV infection.
Means of transmission
HCV is spread primarily by direct contact with human blood. Transmission through
blood transfusions that are not screened for HCV infection, through the reuse of
inadequately sterilized needles, syringes or other medical equipment, or through
needle-sharing among drug-users, is well documented. Sexual and perinatal
transmission may also occur, although less frequently. Other modes of
transmission such as social, cultural, and behavioural practices using
percutaneous procedures (e.g. ear and body piercing, circumcision, tattooing)
can occur if inadequately sterilized equipment is used. HCV is not spread by
sneezing, hugging, coughing, food or water, sharing eating utensils, or casual
contact.
In both developed and developing countries, high risk groups include injecting
drug users, recipients of unscreened blood, haemophiliacs, dialysis patients and
persons with multiple sex partners who engage in unprotected sex.
In developed countries, it is estimated that 90% of persons with chronic HCV
infection are current and former injecting drug users and those with a history
of transfusion of unscreened blood or blood products.
In many developing countries, where unscreened blood and blood products are
still being used, the major means of transmission are unsterilized injection
equipment and unscreened blood transfusions. In addition, people who use
traditional scarification and circumcision practices are at risk if they use or
re-use unsterilized tools.
Prevalence
WHO estimates that about 170 million people, 3% of the world's population, are
infected with HCV and are at risk of developing liver cirrhosis and/or liver
cancer. The prevalence of HCV infection in some countries in Africa, the Eastern
Mediterranean, South-East Asia and the Western Pacific (when prevalence data are
available) is high compared to some countries in North America and Europe.
Diagnosis
Diagnostic tests for HCV are used to prevent infection through screening of
donor blood and plasma, to establish the clinical diagnosis and to make better
decisions regarding medical management of a patient. Diagnostic tests
commercially available today are based on Enzyme immunosorbant assays (EIA) for
the detection of HCV specific antibodies. EIAs can detect more than 95% of
chronically infected patients but can detect only 50% to 70% of acute
infections.
A recombinant immunoblot assay (RIBA) that identifies antibodies which react
with individual HCV antigens is often used as a supplemental test for
confirmation of a positive EIA result.
Testing for HCV circulating by amplification tests RNA (e.g. polymerase chain
reaction or PCR, branched DNA assay) is also being utilized for confirmation of
serological results as well as for assessing the effectiveness of antiviral
therapy. A positive result indicates the presence of active infection and a
potential for spread of the infection and or/the development of chronic liver
disease.
Treatment
Antiviral drugs such as interferon taken alone or in combination with ribavirin,
can be used for the treatment of persons with chronic hepatitis C, but the cost
of treatment is very high. Treatment with interferon alone is effective in about
10% to 20% of patients. Interferon combined with ribavirin is effective in about
30% to 50% of patients. Ribavirin does not appear to be effective when used
alone.
Prevention
There is no vaccine against HCV. Research is in progress but the high mutability
of the HCV genome complicates vaccine development. Lack of knowledge of any
protective immune response following HCV infection also impedes vaccine
research. It is not known whether the immune system is able to eliminate the
virus. Some studies, however, have shown the presence of virus--neutralizing
antibodies in patients with HCV infection.
In the absence of a vaccine, all precautions to prevent infection must be taken
including:
* Screening and testing of blood and organ donors;
* Virus inactivation of plasma derived products;
* Implementation and maintenance of infection control practices in health
care settings, including appropriate sterilization of medical and dental
equipment;
* Promotion of behaviour change among the general public and health care
workers to reduce overuse of injections and to use safe injection practices;
andRisk reduction counselling for persons with high-risk drug and sexual
practices.
For more information contact:
WHO Media centre
Telephone: +41 22 791 2222
E-mail: mediainquiries@who.int
http://www.who.int/mediacentre/factsheets/fs164/en/
Alan
http://www.veloceraptor.free-online.co.uk/index.thml
http://veloceraptor.blogspot.com/
http://theoriginalfirebird.blogspot.com/
http://lordcerneabbastoo.blogspot.com/
http://www.stopwar.org.uk/
http://www.700women.org/
|
|