When first diagnosed 3 years ago my viral load was in the hundred thousands, I believe it was 7 hundred thousand. According to this particular strain, I had been infected for 13 years before detection. Immediately started on sustiva and combivir..the only ones I have ever been on. Now I am undetectable. How does this work?...If the meds only stop reproduction why isn't it still the same level as in the very beginning of diagnosis? How does it lower to become undectable? Does the original virus die? And if it does die why can't someone be cured? I just don't understand...

This is a very good question.

The best antiretroviral therapy lowers the plasma viral load - which is really a test of the amount of HIV RNA in the blood - by 3-5 logs, i.e. it reduced your viral load from 750,000 to 75,000 (one log) to 7,500 (two logs) to 750 (three logs) to <75 (more than 4 logs).

However, HIV is a 'systemic' viral infection, meaning it infects many tissues in the body, including the liver and spleen, lymph nodes, GI tract, skin, gonads, and central nervous system, among others.

Every day in a person with HIV infection there are 10 billion virions produced. The entire viral population is replenished every three days.

Our current HIV medications are static, i.e. they stop the virus from replicating further, but they do not kill all virus in the body. As soon as someone with HIV infection stops their HIV medications, the replication resumes, and the viral load in the blood again becomes detectable, usually at the same level as when the person was first diagnosed.

So....when you started the HIV medications, you stopped most (not all) of your new HIV viral replication, and the viral particles in your blood were cleared faster than they were being produced. Over time, that resulted in a level of plasma HIV RNA below the ability of the test to detect them, i.e. a level of < 50 copies/ml, when at diagnosis the level was 750,000. You still have HIV in the other tissues mentioned above, and you also still have active, though lower level, viral replication and evolution.

Unfortunately, the virus can survive for prolonged periods of time in the form of latent infection in various cell types, including blood cells and cells of the gonads and central nervous system. Its been estimated that effective treatment and cure of existing HIV infections with our current treatments would take 70 years or more. It appears that eradication of HIV - i.e. cure - at the present time cannot be achieved.

So the best that ART has to offer is to slow the disease progression that is usually associated with HIV infection down dramatically, and even to stop further disease progression. This does have the potential to offer a person with HIV infection a normal life expectancy, and many years without any clinical illness from HIV infection. That is not the same as a cure, i.e. the eradication of HIV infection - but it may be almost as good for a person like you, who has had 3 years of near-normal health (while of course having to take ART and adhere faithfully to the regimen).

It's helpful for your health care to understand these issues, as they are also important in the potential for the development of ART drug resistance. I encourage you to talk to your doctor about these questions and this response.