# Chlamydia is a communicable disease caused by the bacterium Chlamydia. Explain how the body's defences and the nature of Chlamydia's transmission make it difficult to prevent the spread of this infection.

> Pearson Edexcel A-Level Biology A (9BI0) — 5.2 Pathogens and infection · Explain · 5 marks

> Chlamydia is one of the most commonly reported sexually transmitted infections in the UK. It is spread through sexual contact and often produces no symptoms in infected individuals, meaning many people are unaware they carry the bacterium.

## Mark scheme (5 marks)

1. Chlamydia is a communicable disease spread through direct sexual contact / transfer of infected bodily fluids
2. Many infected individuals have no symptoms, so they do not seek treatment and unknowingly continue to spread the bacterium
3. The immune system produces antibodies specific to Chlamydia antigens, but this response may not occur fast enough to prevent transmission to others
4. Physical barriers such as skin act as a first line of defence, but sexual contact bypasses these barriers allowing direct transmission
5. If left untreated, Chlamydia can lead to infertility, so early detection / use of antibiotics is important to prevent long-term harm and further spread

## Key terms

- [communicable disease](https://www.gradenine.co.uk/glossary/communicable-disease)
- [Chlamydia](https://www.gradenine.co.uk/glossary/chlamydia)

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/chlamydia-is-a-communicable-disease-caused-c45725d6) · Published by Druglandscape Ltd.