The hepatitis C virus is a small (50 nm in size), enveloped, single-stranded, positive sense RNA virus. It is the only known member of the hepacivirus genus in the family Flaviviridae. There are six major genotypes of the hepatitis C virus, which are indicated numerically (e.g., genotype 1, genotype 2, etc.). Based on the NS5 gene there are three major and eleven minor genotypes. The major genotypes diverged about 300–400 years ago from the ancestor virus. The minor genotypes diverged about 200 years ago from their major genotypes. All of the extant genotypes appear to have evolved from genotype 1 subtype 1b. A seventh genotype - 7a - has also been described.
The hepatitis C virus is transmitted by blood-to-blood contact. In developed countries, it is estimated that 90% of persons with chronic HCV infection were infected through transfusion of unscreened blood or blood products or via injecting drug use or sexual exposure. In developing countries, the primary sources of HCV infection are unsterilized injection equipment and infusion of inadequately screened blood and blood products. There has not been a documented transfusion-related case of hepatitis C in the United States for over a decade, as the blood supply is vigorously screened with both EIA and PCR technologies.
Although injection drug use is the most common route of HCV infection, any practice, activity, or situation that involves blood-to-blood exposure can potentially be a source of HCV infection. The virus may be sexually transmitted, although this is rare, and usually only occurs when an STD that causes open sores and bleeding is also present and makes blood contact more likely.
Transmission
Sexual activities and practices were initially identified as potential sources of exposure to the hepatitis C virus. More recent studies question this route of transmission. Currently, heterosexual vaginal intercourse is thought to be a rare means of transmission of hepatitis C infection. The following are the currently known modes of transmission. There may be other, as yet unknown, means of transmission.
Injection drug use
Those who currently use or have used drug injection as their delivery route for drugs are at increased risk for contracting hepatitis C because they may be sharing hypodermic needles or other drug paraphernalia (includes cookers, cotton, spoons, water, etc.), which may be contaminated with HCV-infected blood. An estimated 60% to 80% of intravenous recreational drug users in the United States have been infected with HCV. Harm reduction strategies are encouraged in many countries to reduce the spread of hepatitis C, through education, provision of clean needles and syringes, and safer injecting techniques. For reasons that are not clear, transmission by this route currently appears to be declining in the USA.
The main risk factor for HCV infection is intravenous drug using. Many studies showed that imprisonment is an important predictor of HBV, HCV and HIV infection. Prison conditions increase the risk of transmission of infections, including blood-borne viral infections; the risk is further increased by the use of unsterile equipment used for injection.Intravenous drug users (IDUs) are at a potential risk for acquiring blood-borne infections by parenteral and sexual routes.
During the VA Testimony before the Subcommittee on Benefits Committee on Veterans’ Affairs, U.S. House of Representatives on April 13 2000, Gary A. Roselle, M. D., Program Director for Infectious Diseases, Veterans Health Administration, Department of Veterans Affairs, stated "One in 10 US Veterans are infected with HCV, a rate five times greater than the 1.8% infection rate of the general population." A study conducted in 1999 by the Veterans Health Administration (VHA) involving 26,000 veterans showed that up to 10% of all veterans in the VHA system tested positive for hepatitis C.
Of the total number of persons who were hepatitis C antibody positive, and reported an era of service, 62.7% were noted to be from the Vietnam War. The second most frequent group is listed as post-Vietnam War at 18.2%, followed by 4.8% Korean War, 4.3% post-Korean War, 4.2% from WWII, and 2.7% Persian Gulf era veterans.
Blood products
Blood transfusion, blood products, or organ transplantation prior to implementation of HCV screening (in the U.S., this would refer to procedures prior to 1992) are all risk factors for hepatitis C.
A cDNA clone from the hepatitis C virus genome was first isolated in 1989 and reliable tests to screen for the virus were not available until 1992. Therefore, those who received blood or blood products prior to the implementation of screening the blood supply for HCV may have been exposed to the virus. Blood products include clotting factors (taken by hemophiliacs), immunoglobulin, Rhogam, platelets, and plasma. In 2001, the Centers for Disease Control and Prevention reported the risk of HCV infection from a unit of transfused blood in the United States is less than one per million transfused units.
Latrogenic medical or dental exposure
People can be exposed to HCV via inadequately or improperly sterilized medical or dental equipment. Equipment that may harbor contaminated blood if improperly sterilized includes needles or syringes, hemodialysis equipment, oral hygiene instruments, jet air guns, etc. Scrupulous use of appropriate sterilization techniques and proper disposal of used equipment can reduce the risk of iatrogenic exposure to HCV to virtually zero. Limitations in the implementation and enforcement of stringent standard precautions in public and private medical and dental facilities is known to be the primary cause of the spread of HCV in Egypt, the country with highest rate of infection in the world.
Blood exposure
Occupation
People can be exposed to HCV through accidental exposure to blood through needle sticks or blood spatter to the eyes or open wounds at work. Universal precautions to protect against such accidental exposures significantly reduce the risk of exposure to HCV.
Recreation
Contact sports and other activities, such as "slam dancing" that may result in accidental blood-to-blood exposure are potential sources of exposure to HCV.
Sexual exposure
Sexual transmission of HCV is considered to be rare. Studies show the risk of sexual transmission in heterosexual, monogamous relationships is extremely rare or even nil. The government does not recommend condom use to prevent hepatitis C transmission in long-term mutually monogamous relationships. However, for not well understood reasons, the risk of transmission is higher if one has multiple sex partners and condom use is recommended. Vaginal penetrative sex is believed to have a lower risk of transmission than sexual practices that involve higher levels of trauma to anogenital mucosa (anal penetrative sex, fisting, or use of sex toys). For these reasons, condom use is highly recommended for those who engage in anal sex play or other sex acts likely to cause bleeding or damage mucosal linings.
Body piercings and tattoos
Tattooing dyes, ink pots, stylets, and piercing implements can transmit HCV-infected blood from one person to another if proper sterilization techniques are not followed. Tattoos or piercings performed either before the mid 1980s, "underground," or nonprofessionally are of particular concern, since sterile techniques in such settings may have been insufficient to prevent disease; sharing unsterilized tattooing equipment (for example, in the prison system) has an obvious increased risk of acquiring HCV. The U.S. Centers for Disease Control and Prevention's position on this subject states that, "Whenever tattoos or body piercings are performed in informal settings or with nonsterile instruments, transmission of hepatitis C and other infectious diseases is possible." Despite these risks, it is rare for tattoos in an approved facility to be directly associated with HCV infection.
Shared personal care items
Personal care items such as razors, toothbrushes, cuticle scissors, and other manicuring or pedicuring equipment can easily be contaminated with blood. Sharing such items can potentially lead to exposure to HCV. Appropriate caution should be taken regarding any medical condition which results in bleeding, such as canker sores, cold sores, and immediately after flossing.
HCV is not spread through casual contact, such as hugging, kissing, or sharing eating or cooking utensils.
Vertical
Vertical transmission refers to the transmission of a communicable disease from an infected mother to her child during the birth process. Mother-to-child transmission of hepatitis C has been well described, but occurs relatively infrequently. Transmission occurs only among women who are HCV RNA positive at the time of delivery; the risk of transmission in this setting is approximately 6 out of 100. Among women who are both HCV and HIV positive at the time of delivery, the risk of transmitting HCV is increased to approximately 25 out of 100.
The risk of vertical transmission of HCV does not appear to be associated with method of delivery or breastfeeding.