0610 · 16.6Sexually transmitted infections

STIs, HIV and AIDS

0:00Why can an infection pass between people through sexual contact, but not through sitting beside someone in a classroom? The answer depends on how the pathogen travels from one body into another. Understanding that route also explains how transmission can be prevented. In this video, we will connect sexually transmitted infections, human immunodeficiency virus, and the measures that interrupt their spread. First, remember that a pathogen is a disease-causing organism or agent, such as a bacterium or virus.

0:28An infection occurs when a pathogen enters the body and multiplies. Transmission means the passing of a pathogen from one person to another. Different pathogens have different transmission routes, so preventing an infection means understanding which route it uses. A sexually transmitted infection, or S T I, is an infection that is transmitted through sexual contact. That is the definition you need, but notice what it does not say. It does not say that sexual contact is necessarily the infection’s only transmission route.

0:57Some pathogens that cause sexually transmitted infections can also pass between people in other ways. Our main example is human immunodeficiency virus, or H I V, a virus that is a pathogen and causes a sexually transmitted infection. Its name gives us a clue about what it does. Immunodeficiency means that the body’s immune defences are weakened. To understand why that matters, we need just one idea about the immune system, which is that it normally helps protect us against pathogens.

1:25Human immunodeficiency virus damages the immune system, specifically cells called lymphocytes. Lymphocytes are white blood cells involved in defending the body against infection. As these cells are damaged, the body becomes less able to fight off other infections. You will explore these defensive cells further in the video on diseases and immunity. Infection with human immunodeficiency virus may lead to acquired immunodeficiency syndrome, known as AIDS. This is the condition in which the immune system is severely weakened, leaving the person vulnerable to other infections.

1:57The virus and the syndrome are therefore not the same thing. A person can have the virus without having developed the syndrome, and treatment can help prevent that progression.

How HIV is transmitted

2:06Now consider transmission as a journey with two requirements. The virus must be present in a fluid that can carry it, and that fluid must have a route into another person’s body. Important fluids include blood, semen, vaginal fluids and breast milk. Simply being near an infected person does not provide that route, which is why ordinary social contact does not transmit this virus. One route is unprotected sexual intercourse with an infected person.

2:32Infected semen or vaginal fluids can come into contact with delicate lining tissues, allowing the virus to enter the body. Small cuts or tears in the lining can also provide an entry route. The important connection is between an infected body fluid and a place where the virus can enter, not simply contact with another person. Another route is sharing needles or syringes contaminated with infected blood. A small amount of blood can remain in the equipment after use.

2:58If another person uses it, that blood can be introduced into their body. A transfusion of infected blood can also transmit the virus, which explains why donated blood must be screened before it is used. The virus can also pass from an infected mother to her baby. This may happen across the placenta during pregnancy, through exposure to infected blood or fluids during birth, or through breast milk after birth.

3:21These are separate opportunities for transmission at different stages. Transmission is possible, not inevitable, and appropriate medical care can reduce the risk. These routes also explain what does not transmit the virus. Hugging, shaking hands, sharing a classroom or sharing ordinary eating utensils does not provide a recognised transmission route. Mosquito bites do not transmit it either. Knowing these distinctions matters because prevention should address genuine transmission risks, rather than encourage fear or unfair treatment of people living with the infection.

Controlling STI transmission

3:51So how do we control the spread of sexually transmitted infections? Think of each measure as breaking a link in the transmission chain. Some measures prevent exposure to infected fluids, while others identify infections and reduce further spread. Using several appropriate measures is more effective than relying on one measure to deal with every possible route. Using condoms correctly during sexual intercourse reduces the risk of transmission by providing a barrier.

4:17This reduces contact between infected sexual fluids and another person’s lining tissues. Condoms reduce the risk, but they do not guarantee protection against every sexually transmitted infection. Limiting the number of sexual partners also reduces opportunities for encountering an infection, although it does not make the risk disappear. Testing is important because a person can have an infection without obvious symptoms. Testing identifies infections so that people can receive appropriate treatment and advice to reduce transmission.

4:45Contact tracing means confidentially identifying and informing sexual contacts who may have been exposed. Those contacts can then be offered testing and treatment, helping interrupt further spread. Treatment depends on the pathogen involved. Antibiotics can treat some bacterial sexually transmitted infections, but antibiotics do not cure human immunodeficiency virus because it is a virus. Medicines called antiretroviral medicines can control this virus and reduce the risk of transmission, but they do not cure the infection.

5:15So testing and treatment remain useful even when treatment is not a cure. Other control measures match the non-sexual routes we have discussed. Screening donated blood prevents infected blood from being used in transfusions. Not sharing needles, and using sterile equipment, prevents blood from being transferred through contaminated equipment. Education supports all these measures by explaining transmission routes, encouraging testing, and correcting misconceptions about how infections spread.

Exam answer: controlling HIV

5:42Let us work through an exam-style example. A clinic screens donated blood, uses a new sterile needle for each patient, and offers testing to people who feel healthy. The question asks you to explain how these measures help control the spread of human immunodeficiency virus. Start by identifying the transmission route each measure interrupts, rather than giving the same vague explanation for all three. For blood screening, the relevant route is transfusion of infected blood, so connect screening to keeping infected donations out of transfusions.

6:12For sterile needles, the route is contaminated blood remaining in shared equipment. For testing, the key idea is that symptoms are not a reliable way to identify everyone who is infected. Each measure has a different reason for working. A suitable answer would be this. Screening donated blood identifies infected donations so that they are not used for transfusions. Using a new sterile needle prevents infected blood from a previous patient being introduced into another patient.

6:39Testing can identify infection in people without symptoms, allowing appropriate treatment and advice to reduce further transmission. Each sentence connects a measure to how it controls spread. Remember to match the command word in a question. If asked to describe a sexually transmitted infection, give the definition, which is an infection that is transmitted through sexual contact. If asked to describe transmission, identify how the virus passes between people. If asked to explain control, connect each control method to the transmission route or opportunity it interrupts.

7:10Let us finish with the central connections. Human immunodeficiency virus causes a sexually transmitted infection, damages lymphocytes, and may lead to acquired immunodeficiency syndrome. Transmission can occur through unprotected sexual intercourse, transfusions of infected blood, shared needles, or from mother to baby during pregnancy, birth or breastfeeding. Control works by interrupting these routes through condoms, testing and treatment, blood screening, sterile equipment, education, contact tracing and limiting sexual partners.