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1 Person - Multiple Strains - Harder to Treat?

Nov 20, 2000

I have heard rumors that I would like to find the truth about. (1)That if I am HIV+ and my partner is as well, that I don't have to worry about safe sex. (2)Multiple strains of HIV exist and that the partners can both end up with two different strains, which is much harder to combat. Which of these, if either, is true. I have talked to many people (though no doctors) about this, and no one seems to have a concrete answer. Thank you, in advance, for breaking down the confusion.

Response from Dr. Pavia

This is an important question, and every infected person should probably pay attention to what we know about it. Basically, the question boils down to: "If I am infected with HIV, can I be infected with another strain through unprotected sex with another positive, and can that hurt me."

The scientific evidence is a cautious yes, based on somewhat limited evidence. However, my personal belief is that the weight of that evidence is pretty concerning.

Piece 1: We have known for at least 3 years that a substantial portion of people who live in areas where 2 or more very different subtypes exist (also known as clades) are in fact infected with more than one subtype. The number has ranged as high as 25% in some studies. You need to understand a few things about the science to realize that if we can find it at all, it may be much more common than we think. First, it is hard to discriminate "strains" of closely related virus, such as might be circulating in San Francisco. It becomes easier to use molecular short cuts whent the strains are very different, which is why more work has been done in areas with more than one subtype exist. Just as resistance testing is likely to only pick up the most common strain, that is a problem with these typing schemes, so we probably underestimate the number of dually infected people. But... from these studies, you cannot be sure that people were infected with first one, then the other.

Piece 2: Many of the most important strains in the world today, such as the subtype E in much of Southeast Asia, arose as recombination between two strains. That means one person must have been infected with both strains for the recombination to occur.

Piece 3: Antibody or cytotoxic lymphocytes from one patient may be much more effective at neutralizing their own strain than virus from another person.

Piece 4. A research group in Alabama took an HIV infected chimp who was doing well, exposed it to another strain of virus, and showed that the new virus infected the chimp. More importantly, the chimp died of AIDS, even though most chimps with HIV remain healthy.

Piece 5, and the most scary: Last year at the retrovirus conference, a group from Canada reported on a man they studied in detail. He was a long term non progressor, but his new lover was very ill and had been treated with many drugs which had failed. The first man suddenly began to have a falling CD4 count. He was started on 3 drugs and there was no response. His virus turned out to be resistant to those drugs, and several he had never seen. They then looked at that virus, his lover's, and samples from before the new relationship. He was infected with one strain before, but now has his lover's highly resistant virus.

So I think the evidence is clear. You can get infected wtih a new strain, and it can be more destructive and harder or even impossible to treat. We don't know how often this happens, or how great the risk is, however, and more research needs to be done. My message to my patients and any positive person is that you should not have unprotected sex with other infected persons, especially if they are casual person, or have been on treatment. Within a long term monogamous relationship the risk may be less, and it may be something to weigh carefully.

Sorry for the long answer, but it is important to know why we think we know what we know. Good luck, and be safe.


Andrew T. Pavia, M.D.

PI vs. NNRTI as First Therapy
crazy idea

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