HEALTH TOPICS A TO Z





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Hepatitis C

Hepatitis C is a viral infection of the liver which had beenreferred to as parenterally1 transmitted "non A, non Bhepatitis" until identification of the causative agent in 1989. Thediscovery and characterization of the hepatitis C virus (HCV) led to theunderstanding of its primary role in post-transfusion hepatitis and its tendencyto induce persistent infection.

HCV is a major cause of acute hepatitis and chronic liverdisease, including cirrhosis2 and liver cancer. Globally, anestimated 170 million persons are chronically infected with HCV and 3 to 4million persons are newly infected each year. HCV is spread primarily by directcontact with human blood. The major causes of HCV infection worldwide are use ofunscreened blood transfusions, and re-use of needles and syringes that have notbeen adequately sterilized.

No vaccine is currently available to prevent hepatitis C andtreatment for chronic hepatitis C is too costly for most persons in developingcountries to afford. Thus, from a global perspective, the greatest impact onhepatitis C disease burden will likely be achieved by focusing efforts onreducing 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 viralhepatitis. It is an enveloped RNA virus in the flaviviridae family whichappears to have a narrow host range. Humans and chimpanzees are the only knownspecies susceptible to infection, with both species developing similar disease.

An important feature of the virus is the relative mutabilityof its genome, which in turn is probably related to the high propensity (80%) ofinducing chronic infection. HCV is clustered into several distinct genotypeswhich may be important in determining the severity of the disease and theresponse to treatment.

Clinical features of acute infection

The incubation period of HCV infection before the onsetof clinical symptoms ranges from 15 to 150 days. In acute infections, the mostcommon symptoms are fatigue and jaundice; however, the majority of cases(between 60% and 70%), even those that develop chronic infection, areasymptomatic.

Chronic infection and consequences

About 80% of newly infected patients progress to developchronic infection. Cirrhosis develops in about 10% to 20% of persons withchronic infection, and liver cancer develops in 1% to 5% of persons with chronicinfection over a period of 20 to 30 years. Most patients suffering from livercancer who do not have hepatitis B virus infection have evidence of HCVinfection. The mechanisms by which HCV infection leads to liver cancer are stillunclear. Hepatitis C also exacerbates the severity of underlying liver diseasewhen it coexists with other hepatic conditions. In particular, liver diseaseprogresses more rapidly among persons with alcoholic liver disease and HCVinfection.

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 medicalequipment, 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 practicesusing percutaneous procedures (e.g. ear and body piercing, circumcision,tattooing) can occur if inadequately sterilized equipment is used. HCV is notspread by sneezing, hugging, coughing, food or water, sharing eating utensils,or casual contact.

In both developed and developing countries, high risk groupsinclude injecting drug users, recipients of unscreened blood, haemophiliacs,dialysis patients and persons with multiple sex partners who engage inunprotected sex.

In developed countries, it is estimated that 90% of personswith chronic HCV infection are current and former injecting drug users and thosewith a history of transfusion of unscreened blood or blood products.

In many developing countries, where unscreened blood andblood products are still being used, the major meansof transmission are unsterilized injection equipment and unscreened bloodtransfusions. In addition, people who use traditional scarification andcircumcision practices are at risk if they use or re-use unsterilized tools.

Prevalence

WHO estimates that about 170 millionpeople, 3% of the world's population, are infected with HCV and are at risk ofdeveloping liver cirrhosis and/or liver cancer. The prevalence of HCV infectionin some countries in Africa, the Eastern Mediterranean, South-East Asia and theWestern Pacific (when prevalence data are available) is high compared to somecountries in North America and Europe.

Table 1: Hepatitis C estimated prevalence and number infected by WHO Region

WHO Region

Total Population

(Millions)

Hepatitis C prevalence

Rate %

Infected Population

(Millions)

Number-of countries by WHO Region where data are not available

Africa

602

5.3

31.9

12

Americas

785

1.7

13.1

7

Eastern Mediterranean

 

466

4.6

21.3

7

Europe

858

1.03

8.9

19

South-East Asia

1 500

2.15

32.3

3

Western Pacific

1 600

3.9

62.2

11

Total

5 811

3.1

169.7

57

 

Source: Weekly Epidemiological Record. N° 49, 10 December 1999, WHO

Diagnosis

Diagnostic tests for HCV are used to prevent infectionthrough screening of donor blood and plasma, to establish the clinical diagnosisand to make better decisions regarding medical management of a patient.Diagnostic tests commercially available today are based on Enzyme immunosorbantassays (EIA) for the detection of HCV specific antibodies. EIAs can detect morethan 95% of chronically infected patients but can detect only 50% to 70% ofacute infections.

A recombinant immunoblot assay (RIBA) that identifiesantibodies which react with individual HCV antigens is often used as asupplemental 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 forconfirmation of serological results as well as for assessing the effectivenessof antiviral therapy. A positive result indicates the presence of activeinfection and a potential for spread of the infection and or/the development ofchronic liver disease.

Treatment

Antiviral drugs such as interferon taken alone or incombination with ribavirin, can be used for the treatment of persons withchronic hepatitis C, but the cost of treatment is very high. Treatment withinterferon alone is effective in about 10% to 20% of patients. Interferoncombined with ribavirin is effective in about 30% to 50% of patients. Ribavirindoes not appear to be effective when used alone.

Prevention

There is no vaccine against HCV. Research is in progress butthe high mutability of the HCV genome complicates vaccine development. Lack ofknowledge of any protective immune response following HCV infection also impedesvaccine research. It is not known whether the immune system is able to eliminatethe virus. Some studies, however, have shown the presence of virus--neutralizingantibodies in patients with HCV infection.

In the absence of a vaccine, all precautions to preventinfection 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.

    Sources: US Department of Health; The World Health Organization


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