Expert: Terry B - 9/23/2006

Question
Dear Terry,

I don't understand how HIV can actually be transmitted. I have read that it is transmitted through semen, vaginal fluid, breast milk, and blood.

Is it only any of the above being in contact with open wounds, or is it possible to get infected if you touch the virus but it doesn't enter the body (ie. no open wounds and you wash your hands immediately)?

Thank you  

Answer
Dear B:

Peace.  Pardon, please, a long answer to a short question, but I thought your excellent question merits a complete response.  

HIV is a retrovirus (meaning that it needs a host cell's DNA to reproduce) found in greater concentration than others in different bodily fluids.  

The fluids most people are most likely to come into contact with are those you listed - blood/blood products, semen, vaginal secretions, and breast milk.  HIV is present in these fluids in sufficient concentration to infect another person - meaning that the virus (which exists primarily in host cells) can come in contact with the cells it targets if it is in proximity, i.e., touching those cells.  

The cells it targets are the same ones the body uses to fight off infection - primarily monocytes, lymphocytes, and macrophagic cells - cells found in the bloodstream, at the site of infections, and the listed fluids above.

Intact skin and mucous membranes protect us from many germs including HIV (viral and bacterial) by providing a barrier between our insides and our outsides.  Some breaks in that barrier can and often do occur, because we inhale, ingest, inject, or otherwise bypass these barriers.  (Note that some pathogens target healthy skin cells or those of the mucousal linings - HIV is not one of them.)   

IF you are exposed to fluids containing HIV, several factors come into play to help you assess your risk.  These include the concentration of the virus in those fluids (example, someone recently infected or late in HIV disease will have more virus in fluids because the body cannot suppress it), the amount of the fluids to which you are exposed, the duration of the exposure (how long you are in proximity to these fluids), the amount of area exposed (that is, how much of your skin or mucousal membranes are exposed to the fluid), the frequency (how often you are exposed), and the route of the exposure/transmission - this last addressing your question about touching these fluids with intact skin.

In measuring risk, one can look first at the route of possible transmission - are there breaks in the skin or mucous membranes?  Is there a concurrent infection such as a Sexually Transmitted Disease that is causing lesions, warts, irritation, or something else that might more easily facilitate transfer of the virus to the target cells?  Does the sexual activity create sufficient friction to cause breaks in these natural barriers, as evidenced by any bleeding or significant irritation?  If the answer to all the above is no, the risk is almost negligible.

Using the same line of questioning regarding the other factors is helpful in continued assessment of risk, and be aware also that some of these overlap.  An example is that douching - forced flushing an internally exposed area with water immediately after exposure - actually increases risk, because while it may reduce the amount of fluids, it tends to spread them out over a larger area and remove some of the mucous the body uses to trap pathogens.  There is some further concern in that certain mucousal membranes, such as those in the large intestine, actually perform a function of extracting fluids from waste material - there are some who see this as high risk as HIV may be contained in those fluids.

Using the factors above in assessing risk should help you understand some things, such as why receptive sex is riskier than insertive sex (more fluid for a longer time over a larger area, etc...).

I hope this has answered your question.

Sincerely,

Terry