Sexually Transmitted Infections IGCSE Biology 0610

Sexually Transmitted Infections: HIV and Other STIs

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

Key concept

Sexually transmitted infections (STIs) are passed from person to person through sexual contact. HIV (Human Immunodeficiency Virus) attacks lymphocytes, weakening the immune system and eventually causing AIDS. Prevention includes using condoms, limiting sexual partners and avoiding sharing needles.

The Cambridge 0610 syllabus focuses on HIV as the primary STI example. Questions test your understanding of how HIV attacks the immune system specifically and why this makes the person vulnerable to other infections.

HIV and AIDS

HIV (Human Immunodeficiency Virus) is transmitted through exchange of body fluids: unprotected sexual contact, sharing contaminated needles, or from mother to child during birth or breastfeeding. HIV does not spread through casual contact, coughing, or insect bites.

The virus specifically attacks lymphocytes, the white blood cells responsible for producing antibodies. As the virus destroys lymphocytes, the immune system becomes progressively weaker. Eventually, the immune system can no longer fight infections. This stage is AIDS (Acquired Immune Deficiency Syndrome). People with AIDS die from opportunistic infections that a healthy immune system would normally control.

Other sexually transmitted infections

Gonorrhoea is a bacterial STI that causes pain and discharge. It can be treated with antibiotics, though antibiotic-resistant strains are becoming more common. Chlamydia is another common bacterial STI that is often asymptomatic, making it easily spread unknowingly.

Genital herpes is caused by a virus and produces painful blisters. Like HIV, viral STIs cannot be cured with antibiotics: they can only be managed. Syphilis is a bacterial STI that can cause serious long-term damage if untreated but is treatable with antibiotics in its early stages.

Prevention of STIs

Methods of reducing STI transmission include: using barrier contraception (condoms) during sexual contact, which physically prevents the exchange of body fluids; limiting the number of sexual partners; regular screening to detect asymptomatic infections early; and not sharing needles or other equipment that may carry infected blood.

For HIV specifically, antiretroviral therapy (ART) can reduce the viral load in an infected person's blood to undetectable levels, significantly reducing the risk of transmission and allowing people with HIV to live longer, healthier lives.

Try a focused question (3 marks)

Explain why a person with AIDS is more likely to die from a lung infection than a healthy person.

Show the answer and marking guidance

HIV destroys lymphocytes, which are responsible for producing antibodies.
With fewer lymphocytes, the person cannot mount an effective immune response.
Pathogens that cause lung infections are not destroyed, so the infection develops and can be fatal.

Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.

Common mix-ups to avoid

Check these points against your own answer before moving on.

Saying HIV is transmitted through casual contact like shaking hands.
Confusing HIV (the virus) with AIDS (the syndrome caused by immune system failure).
Saying antibiotics can cure HIV: antibiotics only work against bacteria, not viruses.
Describing HIV as killing the person directly: death is caused by opportunistic infections the weakened immune system cannot fight.