Although most current HIV-1 antiretroviral drugs were designed for use against subtype B, there is no compelling evidence that they are any less effective against other subtypes. Nevertheless, some subtypes may be more likely to develop resistance to certain drugs, and the types of mutations associated with resistance may vary. This is an important subject for future research.
The effectiveness of HIV-1 treatment is monitored using viral load tests. It has been demonstrated that some such tests are sensitive only to subtype B and can produce a significant underestimate of viral load if used to process other strains. The latest tests do claim to produce accurate results for most Group M subtypes, though not necessarily for Group O. It is important that health workers and patients are aware of the subtype/CRF they are testing for and of the limitations of the test they are applying.
Not all of the drugs used to treat HIV-1 infection are as effective against HIV-2. In particular, HIV-2 has a natural resistance to NNRTI antiretroviral drugs and they are therefore not recommended. As yet there is no FDA-licensed viral load test for HIV-2 and those designed for HIV-1 are not reliable for monitoring the other type. Instead, response to treatment may be monitored by following CD4+ T-cell counts and indicators of immune system deterioration. More research and clinical experience is needed to determine the most effective treatment for HIV-2.25
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