Defining a Cure: Virology and the Hepatitis C Virus
What is a virus?
Virology is the study of viruses. The word “virus” was first used in the late 1500’s, which originated from a Latin word meaning “poison”. A virus is a capsule with DNA or RNA inside. DNA and RNA are molecules that carry genetic information. The virus contains a coat made of protein, similar to a shell, which acts to protect the genetic information inside. Some viruses are further wrapped in an envelope of fat that surrounds them when they circulate outside a cell. Viruses are very tiny and smaller in size than bacteria. They are shaped predominantly as rods or spheres. To survive, viruses are dependent on a host for reproduction. The cycle of infection is similar for most viruses. Infections typically begin when a virus invades a living, normal cell called a host cell and uses the host cell’s molecular tools and machinery to multiply and produce progeny viruses that are clones of the original virus. This eventually kills the host cells, which results in making you sick. Some viruses can induce chronic infections when the virus replicates over the entire remaining life of the host, as may be the case for hepatitis C viral infections. Those with chronic infections are considered carriers of the infectious virus.
What is a Hepatitis C virus?
“Hepatitis” means inflammation of the liver and also can be part of the name of viral infections that affect the liver, including Hepatitis A, Hepatitis B, and Hepatitis C. Each of the hepatitis diseases are caused by different viruses. The hepatitis C virus (HCV) is a spherical, enveloped RNA virus that targets liver cells, known as hepatocytes. When HCV replicates, sometimes mutant viruses are produced. Mutated HCV makes it harder for the immune system to detect. The addition of mutant viruses may explain the variable clinical course and pose a challenge for the development of a vaccine. In fact, there are vaccines to prevent Hepatitis A and B, but there is no vaccine for Hepatitis C. In addition, antibiotics do not work on viruses, because they are designed to target bacteria.
What does it mean to be cured of HCV?
The goal of treatment is to eradicate HCV RNA. By definition, the term “cured” would suggest that HCV has definitively been cleared from the body; however, in some cases HCV RNA may still be detected in the liver of serum-HCV-RNA-negative patients showing ongoing inflammatory changes. A marker for cure is “sustained virologic response” or SVR, which is currently the best indicator of effective treatment. According to the HCV Guidance created by the American Association for the Study of Liver Diseases and the Infectious Disease Society of America, SVR is defined by the absence of detectable HCV RNA in the serum at 12 or more weeks after the end of treatment. According to the World Health Organization, SVR is defined based on detection at 24 weeks after the end of treatment. The World Health Organization also states that most patients with a SVR will remain HCV RNA negative for at least 5 years after stopping therapy. To achieve a SVR, advances in direct-acting antivirals (DAAs) have improved the prognosis for some people with HCV, but it is not a cure for everyone. DAAs target specific parts of the virus and disrupt viral replication, which ultimately interferes with infection. The new DAA medications offer shorter durations of treatment and increased effectiveness, including higher rates of SVR. Depending on the DAA used, cure rates range from 92% to 99%. At this time, there is a continuous effort to develop medical advances in treatments for Hepatitis C that will further improve the cure rate for all patients with Hepatitis C.