Viral Suppression

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Definition:

Viral suppression is defined as, literally, suppressing or reducing the function and replication of a virus. When discussing antiretriviral therapy for HIV, a regimen is considered to be highly successful if it reduces a person's viral load to undetectable levels*. The term "viral load" refers to the number of copies of HIV per mL of blood. In other words, it's the amount of virus in the blood.

Viral Suppression and HIV

In general, people with HIV need to use a combined antiretroviral therapy (cART - also known as highly active antiretroviral therapy or HAART) to achieve long term viral suppression. This is defined aswhere the level of circulating virus in the blood remain quite low or undetectable. Combination antiretroviral therapy is necessary because HIV can mutate when a single drug (also referred to as monotherapy) is used. It is much more difficult for HIV to become drug-resistant in the presence of a multi-drug regimen. That's true even if those drugs are contained in a single pill.

Sometimes, a particular cART regimen cannot help an HIV-positive patient achieve an undetectable viral load,. In such cases new combinations of drugs will be tried until full viral suppression is achieved. However, receiving test results suggesting that HIV levels in the blood are undetectable is not the same as being told you have been cured of the virus.

Even if no virus is present in the blood, HIV infected cells may remain in the body. Therefore, there is the possibility that the virus could begin to replicate (copy itself) again if antiretroviral therapy were to be stopped. Furthermore, having an "undetectable" viral load simply means that there are too few copies of the virus to be detected by current tests.

As such, "undetectable" is a moving target. Twenty years ago tests were less sensitive. Therefore, so-called undetectable viral loads were potentially substantially higher than they are today.

That said, there are many potential benefits to maintaining an undetectable viral load. People whose test results show undetectable viral loads are generally healthier than those people with results showing higher levels of virus in their blood. In addition, people who have achieved an undetectable viral load are also less likely to transmit HIV to their sexual partners. This is the principle that drives treatment as prevention,, or TasP. TaSP is when people with HIV are given early treatment to improve not just their own health but the health of their communities.

Viral Suppression - In General

HIV treatment is the main context in which most people will hear the term viral suppression. However, it is not the only context in which viral suppression is relevant. The body's ability to suppress viral replication and damp down viral load is relevant in discussion of numerous chronic viral infections.

This includes the sometimes sexually transmitted hepatitis viruses. Viral suppression is also a measure of treatment efficacy for these other viruses.

It is important to realize that, as implied above, medical treatment is not always necessary to achieve viral suppression. For some viruses, in some cases, the immune system can lower levels to the point that the virus is not detected in the blood. In other cases, the immune system can eradicate the virus entirely. However, viral suppression is not usually used to describe the process of eliminating a virus from the body. It is usually used to describe situations where the virus has been controlled, but where it is still present at low (or even undetectable) levels. This control can be achieved either  by the immune system or through treatment. 

Examples: Several drugs used as part of an HIV treatment regimen may also be effective at suppressing chronic hepatitis B infection. These drugs are considered to have dual-efficacy against both viruses. HIV and hepatitis are often found together in high-risk patients.

Sources:
Engell CA, Pham VP, Holzman RS, Aberg JA. Virologic Outcome of Using Tenofovir/Emtricitabine to Treat Hepatitis B in HIV-Coinfected Patients. ISRN Gastroenterol. 2011;2011:405390.

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