An antiretroviral pill used to prevent HIV infection has been shown to be effective in intravenous drug users, cutting their risk of contracting the virus in half compared to people who did not take the medication, according to a study published in The Lancet earlier this month. Trans,mission by intravenous drug use appears to account for around one in ten new HIV infections globally and around one in 12 in the United States. The same medication, called tenofovir, has also been found to prevent sexual and mother-child transmission; with this newest study, tenofovir has been shown to protect every major population at risk for HIV infection.
The study, performed in Thailand, also included blood tests performed on subjects, to determine how consistently they took the tenofovir. Intravenous drug users who took the prophylactic medication regularly—at least two-thirds of the time—and so maintained consistent levels of it in their blood found their risk of contracting HIV drop by 74 percent.
HIV, which stands for human immunodeficiency virus, is a retrovirus, which means once it infects a person (or other host), it spreads throughout the body by hijacking cell growth mechanisms. HIV causes AIDS when it infects and deactivates immune system cells; when the immune system is depleted beyond the point at which it is effective at protecting the body from infection, the patient is considered to have AIDS. Weakening the immune system prevents it from attacking HIV, and it also prevents it from attacking anything else, meaning HIV-positive people are susceptible to opportunistic infections by microbes that are common in the environment—or common but dormant in people—but that healthy immune systems successfully fight off as a matter of course.
The virus is usually transmitted through blood or sexual fluids. The most common means of transmission are sexual activities with an infected person without a barrier such as a condom, injecting drugs such as heroin with a syringe used by an infected person, or from an infected mother to her child through the placenta or breastfeeding. Transmission by all these means can be reduced with tenofovir. It is possible for HIV to be transmitted through blood transfusions, but the blood supply in the United States is screened for the virus.