Why Is Understanding Drug Resistance Important?

Part of A Guide to HIV Drug Resistance

HIV is a tough little virus. Although scientists have spent the last 25 years designing medications to fight it, HIV can learn to adapt and avoid these medications. When this happens, we say you've developed "drug resistance."

By the time you've finished reading this booklet, we hope you'll have a much better understanding of how resistance works, how your doctors can test for it and what options you have if you find that your HIV is resistant to one or more HIV medications.

How HIV Works

Drug resistance is easier to understand once you know a little bit about how HIV works. HIV, like all viruses, is a parasite; it needs a human cell in which to reproduce. The first thing HIV does when it enters your body is look for a comfortable place to make its home. Its target? Your immune system -- in particular, cells known as CD4 or helper T cells. The fact that HIV enters these particular cells is bad news, since CD4 cells are what your body uses to fight off infections.

Once HIV gets inside a CD4 cell, it basically hijacks it and transforms the cell from a disease fighter into a factory whose sole mission is to create as many new copies of HIV as it can. These copies then travel to other CD4 cells, infect them and turn them into HIV factories as well. These factories can produce a billion or more copies of HIV per day. The specific number of HIV copies churned out each day will depend on how many CD4 cells are infected and producing virus. The level of production can be measured by your viral load -- the lower your viral load number, the less HIV is multiplying. Although the parent HIV dies soon after it makes copies of itself, it produces so many copies before it dies that HIV remains a continual danger.

While HIV is busily creating copies of itself, it's also destroying your immune system, since soon after it uses your CD4 cells to make copies of itself, the CD4 cells die. This explains why, without treatment, someone with HIV may gradually see his or her CD4 count fall. The lower a person's CD4 count is, the more likely he or she will be to get sick.

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