# Infectious Disease

> CIE A-Level Biology · 9700
> Source: https://www.owlsprep.com/study/cie-9700-u10-overview/
> Weight: n/a

This unit connects microbiology, cell biology, and public health to explore infectious disease, from pathogen biology and transmission to key global diseases, antimicrobial resistance, and population-level disease control.

**Prerequisites:** [Basic understanding of prokaryotic and eukaryotic cell structure](https://www.owlsprep.com/study/cie-9700-u1-cell-structure/); [Foundational knowledge of the human immune system](https://www.owlsprep.com/study/cie-9700-u9-immune-system/)

## Learning objectives

- Classify different types of pathogens and explain their mechanisms of transmission between hosts
- Describe the cause, transmission, progression, and control of three major global infectious diseases: HIV/AIDS, tuberculosis, and malaria
- Explain how antibiotics function and the development and spread of antibiotic resistance
- Evaluate public health strategies used for global control and prevention of infectious disease

## Unit at a Glance

This unit follows a logical arc from foundational concepts to real-world global health challenges. We begin with core terminology: defining what pathogens are and how they spread from host to host. Next, we dive deep into three of the most impactful infectious diseases affecting human populations globally: HIV/AIDS, tuberculosis, and malaria, covering their cause, lifecycle, transmission, and clinical impact. We then explore the use of antibiotics and the growing public health crisis of antibiotic resistance, before concluding with an overview of global strategies to prevent and control infectious disease spread.

Work through the following sub-topics in order to complete the unit:
- [Pathogens and transmission routes](https://www.owlsprep.com/study/cie-9700-u10-pathogens-and-transmission-routes/) — Introduces the five main classes of pathogens and common modes of transmission between hosts.
- [HIV/AIDS](https://www.owlsprep.com/study/cie-9700-u10-hiv-aids/) — Covers HIV structure, replication, transmission, progression to AIDS, and prevention/treatment strategies.
- [Tuberculosis](https://www.owlsprep.com/study/cie-9700-u10-tuberculosis/) — Explores the cause, transmission, latency, pathogenesis, and control of Mycobacterium tuberculosis infection.
- [Malaria](https://www.owlsprep.com/study/cie-9700-u10-malaria/) — Covers the Plasmodium life cycle, vector transmission, symptoms, and control strategies for this parasitic disease.
- [Antibiotics and antibiotic resistance](https://www.owlsprep.com/study/cie-9700-u10-antibiotics-and-antibiotic-resistance/) — Explains how antibiotics work, how resistance develops and spreads, and strategies to combat resistance.
- [Global disease control](https://www.owlsprep.com/study/cie-9700-u10-global-disease-control/) — Evaluates public health strategies, vaccines, and global initiatives for infectious disease control.

## Common pitfalls

- **Wrong:** Claiming antibiotics are effective against viral infections like HIV.
  - Why it fails: Antibiotics target bacterial-specific cellular processes, which viruses do not have.
  - Correct: Remember antibiotics only work against bacterial pathogens, not viruses.
- **Wrong:** Stating malaria is transmitted directly from person to person.
  - Why it fails: Malaria requires the Anopheles mosquito as an intermediate vector for transmission between humans.
  - Correct: Identify the Anopheles mosquito as the required vector for human malaria infection.

## Cheatsheet

| Key Concept | Summary |
| --- | --- |
| Pathogen classes | Viruses, bacteria, fungi, protoctista, and parasites that cause infectious disease |
| HIV target cells | HIV infects and destroys CD4+ helper T cells, crippling the adaptive immune system |
| TB latency | Mycobacterium tuberculosis can remain latent in host lungs for decades before reactivating |
| Plasmodium hosts | Plasmodium requires two hosts: Anopheles mosquito (vector) and human for its full life cycle |
| Antibiotic resistance origin | Resistance arises from random mutations, then spreads via natural selection and gene transfer |
| Herd immunity threshold | $HIT = 1 - \frac{1}{R_0}$: Proportion of immune population needed to stop an epidemic |

## What's next

Begin your study of this unit with the first sub-topic on pathogens and transmission routes to build your foundational knowledge. After you complete all sub-topics in this unit on Infectious Disease, you can move on to the next unit covering the mammalian gaseous exchange system.

- [Pathogens and transmission routes](https://www.owlsprep.com/study/cie-9700-u10-pathogens-and-transmission-routes/)
- [HIV/AIDS](https://www.owlsprep.com/study/cie-9700-u10-hiv-aids/)
- [Tuberculosis](https://www.owlsprep.com/study/cie-9700-u10-tuberculosis/)

---

From [OwlsPrep](https://www.owlsprep.com) — free study guides for A-Level, IB, AP and IGCSE, written against the official syllabus. Canonical page: https://www.owlsprep.com/study/cie-9700-u10-overview/