HIV in saliva

Mouth-to-genital transmission is not biologically impossible. Significant amounts of blood can be released into saliva after brushing the teeth – at least ten times as much as after kissing or eating. Whether the HIV contained in blood would be infectious, or would be diluted and inactivated by saliva is unclear.¹

HIV has also been found in saliva. However, the neutralising effects of enzymes (SLPI) and HIV antibodies make HIV difficult to isolate from saliva, and make its possible infectiousness hard to estimate.

One study found extremely low levels of virus in the saliva of HIV-positive people – one infectious particle per ml. However, another study by the same research team found high levels of HIV in the saliva of several patients with AIDS when they used a more sensitive HIV PCR viral load test. Indeed, in several cases they found higher levels of HIV in saliva than in semen. These findings should be treated with caution because the study was conducted in 1994, when PCR viral load testing was still at an experimental stage, and large differences in viral load were found between samples from the same patients.²

A more recent study found that infectious HIV can be detected at high levels in saliva during the early weeks of HIV infection (the ‘window’ period before antibodies appear), but that levels fall rapidly after this point. Free floating infectious viruses and virus-infected white blood cells (lymphocytes) could be detected in saliva taken from individuals with primary HIV infection attending clinics in North Carolina. In seven out of eight cases, free floating infectious virus could be detected at an average level of 2000 copies per ml, and in five out of eight cases cell-associated virus could be detected at an average level of 20,000 copies per ml.³