Sexually transmitted infections

1. Overview

Sexually transmitted infections (STIs) represent a significant global health challenge. Understanding how these pathogens spread and the methods available to control them is essential for reducing infection rates and protecting the immune system from long-term damage caused by viruses like HIV.

Key Definitions

• Sexually Transmitted Infection (STI): An infection that is transmitted via body fluids through sexual contact.
• Pathogen: A disease-causing organism (e.g., bacteria, virus, fungus, or protoctist).
• HIV (Human Immunodeficiency Virus): A pathogen that weakens the immune system and causes an STI.
• AIDS (Acquired Immunodeficiency Syndrome): A cluster of symptoms and opportunistic illnesses caused by the advanced stage of HIV infection.
• Immune System: The body’s defense system against pathogens, involving white blood cells and antibodies.

Core Content

Understanding HIV and AIDS

HIV is a viral pathogen. It is important to distinguish between the virus (HIV) and the condition it causes (AIDS).

1. Infection: HIV enters the bloodstream and targets specific white blood cells called lymphocytes.
2. Replication: The virus enters the lymphocytes and uses their machinery to create more copies of itself.
3. Immune Destruction: As the virus multiplies, it destroys the lymphocytes. This reduces the body's ability to produce antibodies and fight off other infections.
4. Progression to AIDS: When the lymphocyte count drops below a certain level and the person begins to suffer from multiple "opportunistic" infections (like pneumonia or rare cancers), they are diagnosed with AIDS.

Methods of HIV Transmission

HIV is transmitted through the exchange of specific body fluids (blood, semen, vaginal fluids, and breast milk). Common routes include:

• Unprotected Sexual Intercourse: The most common method of transmission; the virus passes through the mucous membranes of the genitals.
• Sharing Needle/Syringes: If an infected person uses a needle, small amounts of blood remain. If another person uses the same needle, the virus is injected directly into their bloodstream.
• Mother-to-Child: The virus can pass across the placenta during pregnancy, through blood contact during childbirth, or through breast milk.
• Blood Transfusions: In rare cases (or in countries with poor screening), receiving infected blood or blood products can transmit the virus.

Controlling the Spread of STIs

The spread of STIs can be managed through several preventative measures:

• Education: Raising awareness about how STIs are transmitted and how to practice "safe sex."
• Barrier Methods: Using condoms during sexual intercourse prevents the exchange of body fluids between partners.
• Limiting Partners: Reducing the number of sexual partners decreases the statistical likelihood of exposure.
• Testing and Treatment: Regular screening allows infected individuals to start treatment (Antiretroviral therapy for HIV) and notify previous partners so they can be tested.
• Sterile Equipment: In medical settings, using disposable needles and ensuring all blood products are screened for pathogens.

Extended Content (Extended Only)

There are no specific extended curriculum objectives for this sub-topic in the current IGCSE Biology syllabus.

Key Equations

There are no mathematical equations for this topic.

Common Mistakes to Avoid

• ❌ Wrong: Saying "HIV is the same thing as AIDS."
• ✓ Right: HIV is the virus (pathogen); AIDS is the syndrome (collection of symptoms/diseases) that develops after the immune system is severely damaged by HIV.
• ❌ Wrong: Thinking HIV can be spread by touching, coughing, or sharing cutlery.
• ✓ Right: HIV is only spread through the exchange of specific body fluids (blood, semen, vaginal fluid, breast milk).
• ❌ Wrong: Suggesting the contraceptive pill prevents STIs.
• ✓ Right: Only barrier methods like condoms prevent the exchange of fluids; the pill only prevents pregnancy.

Exam Tips

• Command Words: If a question asks you to "Describe" HIV transmission, list the methods (sex, needles, etc.). If it asks you to "Explain" how the spread is controlled, you must say why a method works (e.g., "Condoms are used because they act as a physical barrier to prevent body fluids from mixing").
• Structure and Function: Be prepared to explain how HIV affects the function of the immune system by destroying lymphocytes.
• Real-world Context: Questions often focus on social responsibility, such as why contact tracing (finding people an infected person has been with) is important for public health.
• Language: Always use the full name "Human Immunodeficiency Virus" at least once before using the acronym HIV to demonstrate complete knowledge.