How HIV is Transmitted
“Transmission of HIV infection” refers to
the process by which HIV, a virus,
invades a 
person’s
body. HIV is transmitted to an uninfected person through certain activities
that bring HIV-infected body fluids in contact with the infectable cells
(that is CD4+ cells)
of an uninfected person. Body fluids that transmit HIV include blood
and blood products, semen, pre-seminal fluid, vaginal fluids, other
body fluids that contain blood, breast milk, brain and spinal cord fluid,
fluid around bone joints, and amniotic fluid (1, 2, 3). These fluids
may contain HIV particles and HIV-infected CD4+ cells, both of which
can cause HIV infection.
HIV can reach the infectable cells of an uninfected person either through that person’s blood or through his or her mucous membranes. Mucous membranes are the linings of certain cavities (such as the nose, mouth, vagina, and anus) that produce a protective layer of mucus. Blood and mucus are infectable because they contain the cells that HIV attacks—that is, CD4+ cells.
Unlike many other illnesses, HIV is not transmitted through routine casual contact, through the air, or through insect bites. This is because HIV does not survive well outside of people’s bodies. HIV can be transmitted in the following ways:
Sexual
activities
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Blood and other body fluids
HIV can be transmitted from person to person through transfusions of blood and blood products, such as blood-clotting agents (platelets). HIV can be transmitted through organ, tissue, and bone transplants (7). HIV can be transmitted by splashing mucous membranes (such as eyes) with infected blood or other body fluids (8). HIV can be transmitted by accidental stabs from contaminated
needles or other sharp objects (8). |
HIV
can be transmitted via skin-piercing instruments (such as needles
for injecting drugs, razor blades, tattoo needles, piercing needles,
or circumcision instruments) that are used on more than one person
(5, 6). This is because some infected blood may be left on these
instruments, and then may be inserted into an uninfected person.
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Parent-to-Child
Transmission Conditions for HIV Transmission
The following three conditions must be met for HIV to be transmitted (6).
#1. HIV must be present.
Infection can only happen if one of the people involved is infected
with HIV. Certain behaviors alone, such as anal sex, do not cause HIV
infection.
#2. HIV must be present in sufficient quantity.
The amount or concentration of HIV in the infected body fluid partly
determines whether infection happens. The greater the concentration
of HIV in the body fluid, the greater the chance a person exposed to
the body fluid becoming HIV-infected.
Only a small amount of infected blood, semen, vaginal fluids, menstrual blood, or breast milk is enough to infect someone, while much larger amounts of anal secretions are needed for HIV transmission. It is important to note that there are no known cases of HIV transmission through saliva, tears, sweat, or urine.
Different people also have different concentrations of HIV, depending, in part, on their stage of HIV disease. In the first, primary stage of infection, people have much higher concentrations of HIV in their blood than they do in the middle, asymptomatic stage of infection. Concentrations of HIV rise during the late stage and full-blown AIDS (10, 11). It is therefore more likely that an HIV+ person will transmit HIV to an uninfected sexual or injecting partner during the primary stages of infection and when the infection has progressed to advanced HIV disease (AIDS) than during the middle, asymptomatic stage, which can last several years.
#3. HIV must get into the bloodstream.
It is not enough just to touch HIV-infected fluid to become infected.
Healthy, unbroken skin is an excellent barrier that prevents HIV from
getting into the body. HIV can only enter through an open cut or sore,
or through contact with the mucous membranes of the anus and rectum,
the genitals, the mouth, and the eyes.
Consequences of Myths and Misconceptions about HIV Transmission
There have been many misconceptions and widespread myths over the years as to how HIV is transmitted. Unfortunately, these misconceptions and widespread myths about how HIV is transmitted have often led to unfounded fears, stigma against people living with HIV/AIDS, unnecessary and punitive restrictions, and discriminatory practices. Also, these misconceptions and widespread myths may have diverted attention from focusing on the actual routes of HIV transmission and, as a consequence, may have increased the likelihood that some people would not follow established HIV prevention practices.
References:
1. Chin. J. (Ed.) Communicable Diseases Manual, 17th Edition. Washington,
DC: American Public Health Association, 2000.
2. Mayer, K.H. & Pizer, H.F. The Emergence of AIDS. The Impact on Immunology, Microbiology, and Public Health. Washington, DC: American Public Health Association, 2000.
3. National Institutes of Allergy and Infectious Diseases (NIAID). HIV Infection and AIDS: An Overview. National Institutes of Allergy and Infectious Diseases, National Institutes of Health, U.S. Department of Health and Human Services, October 2003. Retrieved on January 14, 2004 from http://www.niaid.nih.gov/factsheets/hivinf.htm.
4. Osmond, D.H. Sexual transmission of HIV. HIV InSite Knowledge Base Chapter. San Francisco, CA: Center for HIV Information, University of California, San Francisco, 1998. Retrieved on January 14, 2004 from http://www.hivinsite.com/InSite?page=kb-07-02-01.
5. Burack, J.H. & Bangsberg, D. Epidemiology and HIV transmission in injection drug users. HIV InSite Knowledge Base Chapter. San Francisco, CA: Center for HIV Information, University of California, San Francisco, 1998. Available online at http://hivinsite.ucsf.edu/InSite?page=kb-07-04-01.
6. San Francisco AIDS Foundation (SFAF). AIDS 101: How HIV is Spread. San Francisco AIDS Foundation. Retrieved on January 15, 2004 from http://www.sfaf.org/aids101/transmission.html.
7. Donegan, E. Transmission of HIV by blood, blood products, tissue transplantation, and artificial insemination. HIV InSite Knowledge Base Chapter. San Francisco, CA: Center for HIV Information, University of California San Francisco, 2003. Retrieved on January 14, 2004 from http://www.hivinsite.com/InSite.jsp?page=kb-07&doc=kb-07-02-09.
8. Centers for Disease Control and Prevention (CDC). Fact Sheet: HIV and its Ttransmission. Atlanta, GA: Centers for Disease Control and Prevention, 2003. Retrieved on January 14, 2004 from http://www.cdc.gov/hiv/pubs/facts/transmission.htm.
9. Family Health International (FHI). Reducing Mother-to-Child Transmission (MTCT) of HIV. Retrieved on December 3, 2003 from http://www.fhi.org/en/HIVAIDS/FactSheets/reducingmtct.htm.
10. Lawn, S.D., Butera, S.T., & Folks, T.M. Contribution of immune activation to the pathogenesis and transmission of human immunodeficiency virus type 1 infection. Clinical Microbiology Review, 14(4):753-777, 2001.
11. Hare, C. B. Clinical overview of HIV disease. HIV InSite Knowledge Base Chapter. San Francisco, CA: Center for HIV Information, University of California, San Francisco, 2004. Retrieved on June 1, 2004 from http://www.hivinsite.com/InSite?page=kb-03-01-01.
12. Shugars, D.C., Sweet, S.P., Malamud, D., Kazmi, S.H., Page-Shafer, K., & Challacombe, S.J. Saliva and inhibition of HIV-1 infection: Molecular mechanisms. Oral Diseases, 8 (Suppl 2):169-175, 2002.
13. American Association of Blood Banks. “Receiving a Blood Transfusion: What Every Patient Should Know.” Retrieved on October 13, 2004 from http://www.aabb.org/All_About_Blood/Receiving_Blood/receive.htm.
© Sociometrics Corporation, 2004