What Is Hepatitis C?
Many people have heard of the type of hepatitis that is spread by water or food contaminated with the hepatitis A virus. A diagnosis of hepatitis C, however, is often more puzzling. Your doctor has probably given you some basic facts about hepatitis C, and these articles are designed to help you learn more.
"Hepatitis" -- a term that means inflammation of the liver -- can have many causes. At least six distinct viruses are known to cause hepatitis. The first to be discovered were hepatitis A and hepatitis B. In 1989, researchers isolated another virus that causes liver disease. Originally it was named for what it was not: non-A, non-B hepatitis. Now it is known as hepatitis C virus (HCV).
Although all these viruses target the liver, they differ in many other ways. Hepatitis A is generally transmitted in food or water contaminated with the stool of someone with hepatitis A. This virus causes an acute illness that is usually relatively mild and always goes away on its own. Hepatitis B is spread through contaminated blood or via sexual contact with an infected person. It's a more dangerous virus that, in about 10 to 20 percent of cases, can cause persistent infections (called chronic infections), damage the liver over time, and even lead to liver cancer.
Hepatitis C, or HCV, accounts for only about 15 percent of cases of viral hepatitis. Only 15 to 25 percent of those infected with HCV are able to rid their bodies of the infection completely without treatment. The course of the disease varies greatly from patient to patient; as an overview from the National Institutes of Health points out, "At one end of the spectrum are patients who have no signs or symptoms of liver disease... The degree of injury is usually mild, and the overall prognosis may be good."
In most people, however, it causes a persistent, at times serious, illness. Seventy percent of all cases of chronic hepatitis are caused by HCV. In the United States, it is a leading cause of serious liver disease, including cirrhosis (scarring of the liver), liver failure, and liver cancer. In fact, roughly half of all cases of liver cancer in the U.S., are due to hepatitis C. Liver failure as a result of HCV infection is one of the leading reasons for liver transplants in America.
The global threat
Because symptoms are absent or hard to detect, hepatitis C virus usually often goes undetected for years, even decades, before causing serious illness. For that reason, it has been called the "silent epidemic." Yet hepatitis C poses a serious health threat around the world. Worldwide, more than 200 million people are believed to be infected with the virus. An estimated 4.1 million Americans carry it. Of those, approximately 3.2 million have chronic hepatitis C.
In fact, more people are infected with HCV than with the AIDS virus. Hepatitis C is responsible for 10,000 to 12,000 deaths in the United States each year. Many people were exposed to the virus through transfusions of contaminated blood, before researchers identified hepatitis C and created tests to screen for it in the blood supply. Sharing of needles for intravenous drug use also spreads the virus.
A small but devious germ
What makes hepatitis C so dangerous? Part of the answer lies in the nature of viruses. These germs are among the smallest known disease agents. They consist of strands of genetic material containing instructions for creating new viruses, usually wrapped in a protective coating.
On their own, viruses cannot reproduce or propel themselves. But once they invade healthy cells, they take over and turn them into factories that churn out new viruses. Thousands of nearly identical copies of HCV can emerge from an infected cell. These can then infect other nearby cells. In the process of turning cells into virus-producing factories, many viruses ultimately end up killing the cells they invade, although this is generally not the case with HCV.
Even among viruses, hepatitis C is extremely small -- only 50 nanometers. A nanometer is one-billionth of a meter. Hundreds of thousands of hepatitis C viruses could gather on the period at the end of this sentence. In fact, hepatitis C viruses are even smaller than the wavelength of visible light. Hence, they have no color. What makes this vanishingly small virus so dangerous is that it can escape the immune system, whose job is to identify and kill invading viruses and other organisms.
Unlocking HCV's attack strategies
How HCV survives is still partly a mystery. Yet researchers have discovered a few of its strategies. The most important is its ability to change its shape. Each time the immune system produces antibodies against hepatitis C -- molecules designed to latch onto it and destroy it -- the virus changes its outer shape. Then the antibodies no longer lock onto the virus.
HCV uses other strategies to disarm the immune system. In 2003, researchers at the University of Texas discovered that hepatitis C virus produces an enzyme that blocks a molecule the immune system needs to attack foreign invaders. With this "master switch" shut down, the virus can gain a foothold.
Despite these strategies, some people's immune systems are able to fight off hepatitis C and eliminate it. In a majority of people, however, HCV eludes the immune system and causes a chronic, or persistent, infection. The virus goes on infecting new liver cells and using them to multiply and spread. At least three out of four people infected with hepatitis C virus develop chronic infection that causes liver disease. Why some people fight off HCV and others develop chronic infections isn't well understood.
What is now known is that many people with hepatitis C respond well to treatment. One 2007 study of nearly 1,000 hepatitis C patients found that some showed no sign of the disease for as long as seven years. "On average, 50 percent of the people we treat are cured by the treatment," says Emmet Keeffe, MD, chief of hepatology at Stanford University Medical Center.
The different faces of HCV
One reason hepatitis C infection varies may be the fact that there are many varieties of the virus. Researchers have identified at least six genetically distinct types of HCV, called genotypes (a genotype consists of all the genes in a given organism). There are also more than 50 subtypes. Genotype 1 is the most common virus found in the United States.
When someone is found to be infected with HCV, doctors usually test the genotype of the virus so they can make treatment recommendations. Patients with genotypes 2 and 3 are 50 percent more likely to respond to commonly used therapies than patients with genotype 1. Knowing the genotype helps doctors determine the ideal length of treatment. A 24-week course of combination treatment is usually adequate for patients with genotypes 2 and 3, for example. Patients with genotype 1 typically require a 48-week course of treatment.
It is possible to be infected with more than one genotype. People infected with hepatitis C can also be infected with hepatitis B, another virus that can cause chronic liver disease, as well as with HIV, the virus that causes AIDS.
Rapid progress on many fronts
Being diagnosed with hepatitis C is a frightening experience. But it tends to be a slow-moving disease, and many people infected with HCV live for years without ill effects. In addition, important and rapid progress is being made in understanding the virus and its effects. That knowledge is leading to new and better treatments.
Because the disease develops so slowly, many people with hepatitis C can expect to die of old age or other conditions instead. As hepatologist Keefe points out: "More people die with hepatitis C than because of it."
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