The Human Immunodeficiency Virus (HIV) targets and weakens the body’s immune system, attacking CD4 cells, a type of white blood cell that fights infection. If untreated, HIV can progress to Acquired Immunodeficiency Syndrome (AIDS), the most advanced stage of HIV infection. AIDS severely compromises the immune system, making the body vulnerable to infections and certain cancers. Understanding how this virus is transmitted is important for preventing its spread and promoting public health.
Primary Modes of Transmission
HIV is primarily transmitted through specific activities involving the exchange of certain bodily fluids from a person with HIV to an uninfected individual. Sexual contact is the most common way HIV is spread, particularly through unprotected anal or vaginal sex. The thin lining of the rectum makes anal sex, especially receptive anal sex, the riskiest sexual activity for HIV transmission, as tears can allow the virus to enter the bloodstream. Vaginal sex also carries a risk, as HIV can enter the body through vaginal and cervical tissues, or through cuts or sores on the penis. Oral sex carries very low to no risk, though mouth sores or bleeding gums can theoretically increase it.
Sharing needles, syringes, or other drug injection equipment is another common way HIV is transmitted. Infected blood can remain in shared needles or syringes and be directly injected into another person’s bloodstream. This includes equipment used for injecting drugs, hormones, silicone, or steroids. This direct blood-to-blood contact provides an efficient pathway for the virus to spread.
HIV can also be transmitted from a mother living with HIV to her child during pregnancy, childbirth, or through breastfeeding, known as perinatal transmission. Without interventions, the transmission rate can range from 15% to 45%. However, with proper medical care, including antiretroviral therapy (ART) for the mother during pregnancy and for the infant after birth, the risk of transmission can be reduced to less than 1-2%.
Fluids Involved in Transmission
HIV is present in specific bodily fluids from a person with the virus, which must enter the bloodstream of an HIV-negative person for transmission to occur. These fluids include blood, semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk. For transmission, these fluids need to come into contact with a mucous membrane, damaged tissue, or be directly injected into the bloodstream.
Mucous membranes are found inside the rectum, vagina, penis, and mouth, providing a pathway for the virus to enter the body. The virus can also enter through open cuts or sores on the skin. Direct injection bypasses these barriers and introduces the virus directly into the bloodstream. While HIV can be found in other bodily fluids like saliva, sweat, or tears, the concentration of the virus in these fluids is too low for transmission through casual contact.
Activities That Do Not Transmit HIV
Many common activities do not transmit HIV, helping to dispel misconceptions and reduce stigma. HIV does not spread through casual contact such as hugging, shaking hands, or social kissing. Sharing food, drinks, or utensils, or eating food prepared by someone with HIV, poses no risk. The virus is not transmitted through saliva alone.
Contact with everyday objects like toilet seats, doorknobs, or shared swimming pools will not transmit HIV. The virus does not survive well outside the body and cannot be transmitted through air or water. Insect bites, including from mosquitoes, do not transmit HIV because insects do not become infected with the human virus or inject blood from a previous bite. While rare, transmission through biting has only occurred in cases of severe trauma with extensive tissue damage and blood presence.
Preventing Transmission
Several effective strategies can help prevent HIV transmission and reduce infection risk. Consistent and correct use of condoms during every sexual encounter is a highly effective method against HIV and other sexually transmitted infections. Latex or polyurethane condoms offer the best protection, while natural membrane condoms do not protect against HIV.
Avoiding shared needles, syringes, or other drug injection equipment is paramount in preventing transmission, as these items can carry infected blood. Many communities offer needle exchange programs to provide clean equipment. Pre-exposure prophylaxis (PrEP) involves taking a prescribed HIV medicine daily or as an injection by people who do not have HIV but are at high risk of exposure. PrEP is highly effective, reducing the risk of sexual transmission by about 99% and from injection drug use by at least 74% when taken as prescribed.
Post-exposure prophylaxis (PEP) is another preventative measure, involving a short course of HIV medicine taken within 72 hours after a possible exposure to prevent the virus from taking hold. PEP is available from healthcare providers, emergency rooms, or urgent care facilities. Regular HIV testing is also a preventative step, as knowing one’s status allows for early treatment if positive, which can reduce the viral load to an undetectable level, meaning the virus cannot be transmitted through sex.