Is there a minimum viral load needed to successfully pass HIV infection to
another person? Does it also depend on the mode of transmission [ie. semen to
blood, semen to mucous etc.]. Also are there tests available to determine the
viral load in semen? Thanks
Hi. Thank you for your question. There is no specific "minimal viral load" required for infection to occur. Simply put, the higher the viral load, the higher the likelihood for transmission to occur. Likewise, the lower the viral load, the lower the likelihood for transmission to occur. The mode of transmission can also affect the likelihood of transmission, as is discussed in numerous questions throughout this website. For example, activities like unprotected vaginal or anal intercourse are much more likely to transmit HIV, as compared to activities like receiving oral sex or mutual masturbation.
As far as tests to measure the viral load in semen, there are tests that have been used to measure seminal viral load, but these tests are being used for clinical research studies only. They are not available to the general public. Clinically speaking, there really is no need for testing the viral load in semen, outside of clinical research studies. Past research studies have shown that the viral load in semen roughly correlates with the viral load in the blood (see the question "Viral loads and infectiousnous" for more information on this topic).
Recent studies have also shown that in HIV positive men with Gonorrhea and Non-Gonococcal Urethritis (most commonly due to Chlamydia), the HIV viral load in semen increases while the infection is present. This is especially true with HIV positive men co-infected with Gonorrhea. In other words, when an HIV positive man has these infections, he is more infectious to others, as far as
HIV is concerned. When these infections are treated with antibiotics, the
viral load in semen decreases once again. Antibiotic treatment does not
affect the viral load in the blood. This really should come as no surprise,
since infections like Gonorrhea and Chlamydia cause CD4 cells to enter the
infected area (like the urethra), as a part of the immune systems attack
against these infections. So, if an HIV positive man has Gonorrhea or
Chlamydia in the urethra, the HIV viral load in semen increases while the
infections persist. This information gives even more support for the continued
need for safer sex practices, in persons already infected with HIV.
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