Understanding Hepatitis C Genotypes

There are several different genotypes of the hepatitis C virus (HCV). These can play a role in treatment planning. They also help us understand how the virus might behave.

What is a genotype?

The word genotype refers to genetic material. Each person has their own genotype based on their genes and DNA. This is what makes us all unique. Viruses like HCV also have a genotype. Genotypes can be further broken down into subtypes based on their differences. This can be very confusing when understanding a diagnosis of HCV.^1,2

As viruses like HCV multiply, they need to copy their genetic material. Over time, they make mistakes in the copying process. This leads to changes (mutations). Mutations can cause enough differences that new genotypes are made. Although HCV is copying itself regularly, it takes time to make enough changes for a new genotype to form. In the meantime, smaller changes can build up and lead to different subtypes within a genotype.^1,2

Genotypes and their subtypes make it challenging to make a vaccine against HCV or treat the long-term infection. HCV is constantly changing. Experts cannot always predict what it is going to do next. Also, genotypes allow for re-infection. If a person has cleared or been cured of their HCV, they can get re-infected with a different genotype.³

What are the HCV genotypes?

There are 7 HCV genotypes. They are numbered 1 through 7. There are also over 65 different subtypes across the genotypes. The subtypes are given letters, like genotype 1a or 1b.^1-3

Certain genotypes are more common in different areas of the world. In the United States (US), genotype 1 (and subtypes 1a and 1b) is the most common. About 75 percent of people in the US with HCV have genotype 1. Genotypes 2 and 3 are in the US, too. They make up about 20 to 25 percent of all HCV infections in the US. Other genotypes are less common.^1,2

Outside of the US, genotypes 2 and 4 are common in areas like Egypt and central and western Africa. Genotypes 3 and 5 are often in South Africa, India, China, Taiwan, and Southeast Asia. However, these are just common patterns. It is still possible to get any genotype regardless of where you live.^1,2

When is knowing your genotype helpful?

The genotype of a person’s HCV can be found through a blood test. This test looks at the genetic material in that person’s specific HCV case. Knowing the genotype may be helpful in predicting how HCV will behave. For example, people with genotype 1 are more likely to clear the virus on their own without treatment. People with genotype 3 are more likely to develop fatty damage to their liver. Genotypes 1, 2, and 3 have similar rates of:^3,4

• Cirrhosis
• Liver failure
• Liver cancer

Genotypes were originally most helpful in planning treatment. This was before some of the newer direct-acting antiviral drugs (DAAs) came out for HCV. Some genotypes could only be treated with specific drugs. In addition, certain genotypes responded differently to older treatments like interferon and ribavirin. To make treatment decisions and predict outcomes, it was helpful to know what HCV genotype was involved.^1-4

Thankfully, some newer DAAs target all genotypes of the virus. In the US, these options make it possible to start treatment without further testing. In fact, some doctors may not even test for genotype unless a person does not respond to treatment or has significant scarring of the liver (cirrhosis).^3-5