system
Given the following post, respond as if you're commenting on Reddit:
human
How is HIV so effective at evading the immune system, despite it only having ~9,000 base pairs and 9 genes in its genome?

This seems pretty crazy to me. How can a virus be so effective with such little data?
gpt
HIV is a retrovirus meaning it takes its RNA genome and uses your cells to convert it to DNA and then integrates that DNA into your cells genome. It is really difficult to get rid of something that integrates into the genome like that, really our best defense at that point is to destroy the cell. Our immune system relies on immune cells called T cells to help do this, unfortunately HIV happens to infect a subset of T cells so the immune system is ultimately weakening itself. In addition to this retroviruses are prone to mutation which allows HIV to rapidly alter its antigens further evading our immune system.

That is also why it is so difficult to cure HIV. We have very effective antiretroviral drugs that can get levels of the virus so low they are undetectable, but its genome is still present in the bone marrow and if the drugs were stopped it would come back.

*Edit: More generally viruses can get away with small genomes because they use existing machinery in cells. Rather than carry instructions for a whole factory they just need to carry instructions for one product, the virus. Viruses are still quite complex, they can quickly take over protein production and some can counter intracellular defenses or even force the host cell into stages of the cell cycle that benefit the virus.*