10.1 Infectious Diseases

2026 📋 Syllabus Objectives

By the end of this subtopic, you should be able to:

  1. State that infectious diseases are caused by pathogens and are transmissible
  2. State the name and type of pathogen that causes cholera, malaria, TB, and HIV/AIDS
  3. Explain how cholera, malaria, TB, and HIV are transmitted
  4. Discuss the biological, social, and economic factors involved in the prevention and control of cholera, malaria, TB, and HIV

1. What Are Infectious Diseases?

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A disease is an illness or disorder that causes poor health in the body or mind.

An infectious disease (also called a communicable disease) is a disease that:

  • Is caused by a pathogen — a tiny living organism (or particle) that invades the body and causes harm
  • Is transmissible — meaning it can be passed, or spread, from one person to another (or from animals to people)

Compare with non-infectious diseases: Not all diseases are infectious. For example, lung cancer and sickle cell disease are not caused by pathogens and cannot be spread between people. They may be caused by lifestyle choices, genes, or life events instead.

2. Pathogens and the Diseases They Cause

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There are different types of pathogens — bacteria, viruses, protists (also called protoctists), and fungi. For AS Level, you need to know the following four diseases:

DiseasePathogen NameType of Pathogen
CholeraVibrio choleraeBacterium
MalariaPlasmodium falciparum, Plasmodium malariae, Plasmodium ovale, Plasmodium vivaxProtist (Protoctist)
Tuberculosis (TB)Mycobacterium tuberculosis, Mycobacterium bovisBacterium
HIV/AIDSHuman Immunodeficiency Virus (HIV)Virus

Quick Explanations of Pathogen Types

  • Bacterium — a tiny, single-celled living organism (a prokaryote — meaning it has no nucleus). Bacteria can multiply rapidly inside the body.
  • Protist (Protoctist) — a single-celled organism that is more complex than a bacterium (a eukaryote — meaning it does have a nucleus). Protists like Plasmodium can complete part of their life cycle inside the human body.
  • Virus — not technically a living organism; it is a tiny particle made of genetic material surrounded by a protein coat. Viruses invade body cells and take over them to make copies of themselves.

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