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Different strains = Different RNA/DNA?
Dec 14, 1996

Doc, Keep up the good work. I recently read that Qualitative PCR was negative for the LA Group O infected lady until Group-O specific peptides were used for the test. I thought that PCR looked for the RNA/DNA of the virus. Do different strains then have diff. DNA/RNA? If so, then wouldn't it be impossible to develop a test that can accurately detect all strains, since even the DNA/RNA vary widely (what more the antibodies produced)? In general, can a test that looks for the virus itself (ie. PCR/bDNA) be any more accurate at discovering for unusual/undiscovered strains than current serology tests? Finally, how accurate are viral cultures as a test? Also, what technique was used to isolate HIV for the 1st time in the early 80's, and wouldn' this be considered the most accurate "test"? Thanks.

Response from Mr. Sowadsky

Hi. Thank you for your question.

The group "O" strain of HIV-1 is very unusual. This unusual strain will not usually be picked up by conventional PCR tests. However, the PCR tests that are in use, should pick up most other strains of HIV-1. Luckily, Group "O" is a very rare strain, with about 100 cases worldwide, most of which are in central and western Africa. Different strains do have differences in their RNA and DNA, but the PCR looks for stretches of RNA/DNA that are common to most strains of HIV. But the parts of the RNA/DNA that the conventional PCR tests look at, are different in the Group "O" strain. Therefore this test will pick up most strains of HIV other than Group "O". We must remember that Group "O" is the rare exception when it comes to HIV-1. The properties of this strain are quite unusual as compared to other strains of HIV (when it comes to testing).

Every test has its pros and cons, and I have discussed this in detail in many other previous questions. Currently available antibody tests will pick up the vast majority of strains of HIV. Even in the rare Group "O" strain, the antibody tests were usually able to detect the infection (but not always). I must strongly emphasize that Group "O" is extremely rare worldwide, and there will never be a test that will work 100% of the time. In nature, there will always be rare exceptions and unusual situations. Group "O" HIV-1 falls under that category.

Viral culture tests can take many weeks to perform. They will not always pick up an infection, and are not designed for routine testing. If the tests are positive, that's the gold standard that a person is infected. But again, these tests cannot be used for routine testing.

The antibody tests will pick up the vast majority of HIV strains out there. The same goes for the PCR tests. But no test will ever work 100% of the time.

In all honesty, I don't know what was the very first test to find HIV in the early 1980's. All I can say is that we now have a variety of tests that can be used to find HIV infection. These include antibody tests, PCR tests, antigen tests, and viral culture tests. Also, the quality of tests today have improved since the early 1980's. We have also been able to see the HIV virus itself using special microscopes.

If you have any further questions, please feel free to contact the Centers for Disease Control at 1.800.232.4636 (Nationwide).



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