Hi, our topic for today is the sexual transmission of HIV. In our last session we identified the bodily fluids that carry HIV. Here's the list we used. All of the items on this list, with the exception of breast milk, are relevant to sexual transmission. During various types of sexual acts, all of these fluids may move from one person to another, carrying HIV along to that other person. Tears, saliva, urine, and feces do not carry HIV. But in very rare cases they may be dangerous if they are mixed with quantities of infected blood. There a few more basic facts that we need to emphasize before we talk about the risks of sexual behaviors. We already know that HIV infects white blood cells. We will learn many more details about that in future sessions, but for today, we need to keep this basic fact in mind. If HIV is to be transmitted from one person to another, it must reach that second person's bloodstream. That can happen if the virus finds a mucous membrane that will allow it to pass into the blood, or if it finds damaged tissue, a sore, a tear, a lesion, that will allow it to enter the bloodstream. These are the two ways that HIV gets transferred during sexual transmission. Mucous membranes are in the vagina and cervix, urethra, rectum, and mouth. Damaged tissues may be the result of sexually transmitted diseases, sexual activities, or other injuries. One last introductory remark. A basic fact about the transmission of HIV is that the more virus there is in the infected person, the more likely it is that the receiving person will become infected. We won't talk about it much today, but later in the course we will become familiar with the concept of viral load. At some stages of the, the infection, a person will have a high viral load, a lot of virus particles in the blood. At other stages, and in treatment, people will have lower viral loads, fewer viruses in the blood. Again, the higher the viral load of the infected person, the more likely he or she is to transmit the virus to a sex partner. Here are some images and symbols we will be using today when we discuss the risk of various types of sexual activity. We'll use the obvious figures of a man and a woman. And when we're indicating that someone is carrying HIV we'll place a schematic diagram of HIV next to the figure and label them as HIV positive. We'll use this blue arrow to note the direction of the possible movement of HIV from one sex partner to another. The arrow does not indicate anything about the sexual behavior of the person. Whether for example, that person is an active or a passive participant in a particular sexual act. We will discuss the sexual transmission of HIV in some detail today, but the basic facts are easy to summarize. Anal and vaginal sex are the riskiest sexual behaviors. One type of oral sex has real risk also. So we begin now with the highest risk sexual behavior, anal sex without a condom. The infected partner here is a man and his role in this exchange is to insert his penis into the anus of another man or a woman. These other partners are at relatively high risk, both because the HIV may reach mucus membranes in the rectum and because there is the possibility that the anal or rectal tissue may tear during sex. But what if the receptive partner, male or female, is infected? What is the risk to the HIV negative insertive partner? That situation is represented in this slide. The HIV negative man is, in fact, at risk. The rectal fluid and the blood of the infected man or woman may carry HIV. And there are mucous membranes in the insertive partner's urethra, the opening at the tip of the penis. If there is a sore or other damaged tissue on the penis, that is another possible route of infection. There is one more point to make about this scenario. If the HIV negative man is circumcised, the risk of infection will be somewhat reduced. We won't explain this now, but we will discuss it in detail when, later in the course, we talk about circumcision as a public health prevention technique. Anal sex without a condom, in any of these configurations, is risky. What about vaginal sex without a condom? Vaginal sex without a condom is also a high risk sexual behavior. These images represent vaginal sex in which the man is infected. The woman is at risk because the vagina and cervix are lined with mucus membranes. The vaginal lining can also sometimes tear, or there may be damaged tissue for other reasons. Perhaps an STD, creating other routes for HIV infection. Here is a representation of vaginal sex in which the woman is the HIV positive partner. Vaginal fluid contains HIV particles. And the urethra has mucus membranes. Again, damaged tissue on the penis is another possible point of entry for HIV. This is another instance in which circumcision is somewhat protective. Now, the risk of oral sex. One type of oral sex carries lower, yet significant, risk of HIV transfer. The other types of oral sex involve much lower, virtually zero risk. We start with mouth to penis oral sex in which the insertive partner is HIV positive. The receptive partner is at risk for infection, because semen may carry HIV, and because the mouth contains mucus membranes and may also contain damaged tissue. I will talk about other types of oral sex in a moment. But it is important to pause now to say that we have just covered all of the types of sexual behaviors that carry significant risk of HIV transmission. You may have found this presentation difficult, because I have expressed the levels of risk in vague terms. I described anal sex as high risk. Why haven't I told you that an HIV negative receptive partner who has anal sex with an HIV positive insertive partner has a 1% or a 25% or 50% or 80% chance of being infected? Why do I simply say that it's a high risk behavior? The reason is that the actual danger depends on so many things. Viral load, is the HIV person in the, in treatment? If so, his viral load may be low or undetectable. The sexual exchange will be much safer. Was he recently infected? Infected one year ago? Five years ago? This may also determine whether his viral load is lower or higher. Did the couple use lubrication? Thus lowering the risk of torn or damaged tissue. Was the sexual behavior rough or gentle? Do the partners have a history of sexually transmitted infections? The risk of HIV infection from any particular sexual act depend on these multiple factors. And general discussion, like today's session, can only use the vague terms about risk that we have been employing. It's important for young, for you to understand that this is not evasive, it's simply honest. Risk varies greatly with particular circumstances. Having made these important points, let's return to our review of the various types of oral sex. In each of the following cases, there is virtually no risk of HIV transmission. But in each case one can construct an unusual scenario that involves a lot of blood and damaged tissue that would in fact involve the transmission of HIV. In a world with so many people and so many sexual acts any possible scenario may occur from time to time. So I will say that there is virtually no risk, but I also want you to keep in mind that unusual circumstances may bring real risk back into the picture. In this case, the receptive partner is HIV positive and the insertive partner is HIV negative. The urethra is a possible point of entry for HIV, as is any damaged tissue on the penis, but there's only risk to him if the receptive HIV partner has experienced bleeding in the mouth. The saliva is not a source of HIV. The risk of HIV transmission is close to zero. These images represent the case in which an HIV positive woman receives oral sex from another person. Her vaginal fluid and any blood present in her vagina will carry HIV. The mouths of her partner have mucus membranes. But there is almost no risk to the partner, unless there is severely damaged tissue in the mouth also. There are a couple of other possibilities to consider. Again, sexual situations that involve virtually no risk. If an HIV negative woman receives oral sex from an HIV positive person, there is virtually no risk to her. Saliva doesn't carry enough HIV to be contagious. And it would take substantial bleeding in the mouth to create any risk. Finally there is mouth to anal sexual interaction, rimming. There is virtually no risk here of HIV transmission, although some other risks of infection are sometimes present. As we have reviewed the various types of risky and non-risky sexual actions, we have included several instances where the partners were both women. But the question is often asked, so let's be explicit about lesbian sex. There is virtually no chance of HIV transmission in woman-to-woman sexual exchanges. I've said that there is always the possibility of unusual circumstances, and indeed, there has been one recent documented case of woman-to-woman transmission. In that case there was substantial blood involved along with a rough sexual exchange and damaged tissue. A careful scientific study of the HIV that was present in both women's bodies confirmed that transmission had occurred. Yet this kind of case is extremely rare and we are still justified in saying that woman-to-woman sex involves virtually no risk of transmission. Well, that's a fairly complete review of how HIV can, can be transmitted se, sexually. Let's conclude with reference to the world's favorite nongential interaction. You know the drill. Saliva doesn't contain enough HIV to be contagious. There is virtually no danger of HIV transmission in kissing.
