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Hepatitis C is a serious liver disease caused by the hepatitis C virus. A virus is a type of "germ" that is much smaller than a cell. Viruses copy themselves in cells, and this causes the disease.
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What is hepatitis C virus?
Hepatitis C is a liver disease caused by hepatitis C virus (HCV). A virus is a small piece of genetic material (DNA or RNA) surrounded by a protective layer of protein. Some viruses have another protective layer made of lipids (waxes or oils) called an envelope surrounding them. HCV (Figure 1) has a single piece of RNA inside a protein shell, which is surrounded by a lipid envelope. The envelope has two viral proteins in it (the envelope proteins).
A virus has only one purpose, and that is to make more viruses like it. Viruses copy themselves by entering cells and forcing the cells to make new viruses. This can damage the cells and cause disease. It can also signal the body's immune system to attack the cells to kill the virus. The attack of the immune system on the cells can also cause disease.
HCV does not directly damage the liver. Rather, it causes the immune system to attack the liver, and that causes the disease.
HCV Replication: (Figure 2). HCV sticks to the outside of liver cells using the viral proteins in the envelope. It enters the cells when the viral envelope joins with the cell's outer edge, which is a lipid layer similar to the viral envelope. Once inside the cell, the viral RNA gets out of the protective protein shell. The RNA then causes the cell to make the proteins that HCV needs to copy itself. Some of these proteins (the non-structural proteins) do the work of making more copies of the HCV RNA. Other HCV proteins (the structural proteins) form the new viruses. The new viruses are then pushed out of the cell so they can infect other liver cells.
HCV does not kill the cells it infects. Instead, it turns them into virus factories that keep on making more viruses for the life of the cell.
Viruses have genes, just like cells do. HCV's genes are on a single piece of RNA that is made from about 9,600 nucleotides, like a necklace is made of a string of beads (Figure 3). The nucleotide "beads" come in 4 types, called A, G, C, or U. The pattern of the nucleotides determines what the gene will do, just as a pattern of letters makes a word.
A gene can be slightly different in different people. For example, African Americans have darker skin than Caucasian Americans because there are a few differences in the genes that control their skin color. Virus genes can vary also, and HCV has an unusually large number of differences between viruses infecting different people. There are enough differences in its genes that there are at least 6 different types (genotypes) of HCV. Most Americans with HCV are infected with HCV genotype 1. The differences in the HCV genes can cause differences in how viruses behave. For example, HCV genotype 1 is harder to remove from the body with drugs than is genotype 2.
The pattern (or sequence) of nucleotides of the HCV in a person can change with time. Because the nucleotide sequence controls how the genes work, a change in the HCV genes can change how the virus behaves in a person. For example, the virus may change as it avoids the immune system or avoids drugs taken to kill it. The ability of HCV to change its genes quickly helps it to stay in a person's body for a long time.
Figure 1. Hepatitis C virus. HCV is shaped like a ball, but this picture shows it cut in half. The HCV RNA (black line) is inside the viral core particle (blue). The core particle is made by the HCV C gene. The core particle is surrounded by a lipid envelope (orange) with two HCV envelope proteins in it (green). The envelope proteins are made by the HCV E1 and E2 genes.
Figure 2. HCV Replication. HCV binds to a liver cell (orange square), enters the cell, and releases the viral RNA (black line). The RNA causes the cell to make more viral proteins (blue and green), and some of these proteins copy the RNA to make more RNAs. The new RNAs and proteins combine to make more HCV viruses, which are pushed from the cell without killing it. The new HCV viruses can infect other cells.
Figure 3. The HCV Genome. The HCV RNA is shown as a red line with a box in it. The genes are shown as white and yellow parts of the box. The structural genes that make the proteins that end up in the virus are all on the left, and the non-structural genes that copy the viral RNA and help control the cell are on the right.
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