Research
Hepatitis C is an infectious disease caused by an RNA virus—the hepatitis C virus (HCV). This virus causes chronic infection in over 85 percent of infected individuals, often leading to chronic liver disease. HCV is unrelated to any of the other known hepatitis viruses (A, B, D, and E), and infection is identified by the detection of viral RNA and antibodies to the virus in the blood. Unlike many other infections, the presence of antibodies in the blood does not signify recovery.
Worldwide, some 180 million people are chronically infected with HCV, with over 4 million in the United States. The Institute of Medicine has classified hepatitis C as an emerging infectious disease.
The Disease
HCV can be contracted through the transmission of infected blood or body fluids, e.g., by transfusions, needle-sharing, sexual intercourse, or from an infected mother to her baby. However, since the availability and mandatory adoption of reliable blood screening regimens in 1992, the risk of transmission of HCV via blood transfusion has fallen to less than one per million units of transfused blood, according to the Centers for Disease Control and Prevention (CDC). The majority of new HCV infections now occur among intravenous drug users.
Most acutely and chronically infected people are relatively free of physical symptoms and, in fact, are not even aware of their being infected. HCV causes damage to the liver, the extent of which can only be determined by microscopic examination of a liver biopsy. Symptoms of liver damage may not be apparent for years and, unfortunately, by the time serious liver disease is diagnosed, the liver damage can be considerable and even irreversible—often resulting in end-stage liver disease, cirrhosis, and primary liver cancer. The rate of progression of chronic HCV-related liver disease is variable, and slow for most individuals; for example, approximately 20 percent of individuals progress to cirrhosis after 20 years of chronic infection. Alcohol and other hepatitis viruses are associated with faster progression of the disease—therefore, infected individuals are advised to avoid alcohol consumption, and to be vaccinated against hepatitis A and B. At present, vaccines are unavailable for HCV and the hepatitis E virus (HEV).
Treatments
The current standard of care treatment for hepatitis C is a combination of pegylated interferon and ribavirin, which is intended to achieve a sustained elimination of HCV from the blood. However, the response to this treatment is variable, depending on the variant (genotype) of the infecting virus. Moreover this therapy is associated with significant side effects. Although treatment response is unpredictable, it is best in patients infected with HCV genotypes 2 or 3 (~75%), but considerably less in those infected with HCV genotype 1 (~45%), the predominant strain in the United States
Challenges and Research Priorities
Hepatitis C virus infection is an increasing public health concern. Without more effective antiviral and immunological therapies , the Centers for Disease Control and Prevention (CDC) predicts that deaths due to HCV will double or triple in the next 15 to 20 years due simply to the length of time most people in the United States have been infected.
Better treatment strategies will stem from better understanding the mechanisms of virus replication and pathogenesis. One of the great research challenges is to identify the immune responses that are responsible for the clearance of an acute infection, which occurs spontaneously in a small subset of infected individuals. The successful development of vaccines will depend on overcoming this challenge.
Importance of Increasing Awareness
The fact that most people who are infected with HCV lack symptoms (even if they have been infected for several years) makes it important for individuals at high risk to be tested for HCV so that treatment may be initiated as early as possible. People at high risk include those who have had transfusions of blood or blood products prior to the routine implementation of blood testing, and others who have a greater risk of exposure, such as health care professionals, hemodialysis patients and those with intimate contact with infected persons.
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