Germ Warfare

Germ Warfare

Every day your body is under attack from **pathogens**, and it fights back. This module maps the whole battle: the invaders, the diseases they cause, your defences, and the weapons (vaccines and antibiotics) that turn the tide. A **pathogen** is a microorganism that causes **communicable** (infectious) disease. There are four types: **viruses, bacteria, fungi and protists**, and they spread by **direct contact**, in **water**, in **food**, through the **air** (droplets), or via a **vector** (a carrier such as an insect). Big topic, but the marks come from **naming the specific pathogen and example** each time.

What is a pathogen?

Which is the best definition of a **pathogen**?

• A microorganism that causes communicable disease
• Any microorganism
• A white blood cell that fights infection
• A protein that fights infection

Type and example

Trace the routes

Measles is spread by inhaling _____ from coughs and sneezes. HIV is spread by sexual contact or the exchange of _____. Malaria is spread by a mosquito, which acts as a _____.

The rogues' gallery

The seven diseases to know, with the pathogen type that names each one: • **Measles** (virus): spread by inhaling **droplets** from coughs and sneezes; fever and a red skin rash; can be dangerous. Prevented by vaccination (MMR). • **HIV** (virus): spread by **sexual contact** or exchange of body fluids (e.g. shared needles). It attacks immune cells; untreated it leads to **AIDS**. Controlled with antiretroviral drugs. • **Tobacco mosaic virus** (virus): a **plant** virus giving leaves a mosaic discolouration that reduces photosynthesis and growth. • **Salmonella** (bacterium): food poisoning from contaminated food; fever, cramps, vomiting and diarrhoea caused by **toxins**. UK poultry are vaccinated against it. • **Gonorrhoea** (bacterium): a sexually transmitted disease; treated with **antibiotics** and prevented with condoms. • **Rose black spot** (fungus): black spots on rose leaves that then yellow and drop; spread in water and wind; treated with fungicides. • **Malaria** (protist): spread by a **mosquito vector**; recurrent fevers. Prevented by stopping mosquitoes breeding and using nets.

How each spreads

Two lines of defence

Your body stops pathogens twice: once before they get in, and again once they do.

Complete the defences

The _____ is a physical barrier that also makes antimicrobial secretions. In the trachea, mucus traps pathogens and _____ waft it away from the lungs. The stomach kills swallowed pathogens with _____. If a pathogen gets past all of these, a white blood cell can engulf and digest it by _____.

What do antibodies do?

Exactly how do **antibodies** help defeat a pathogen?

• They lock onto it, clump them together and mark them for destruction
• They directly poison and kill the pathogen
• They engulf and digest the pathogen
• They neutralise the pathogen's toxins

Vaccination and herd immunity

Four words carry every vaccination mark:

Order the response

Put the steps of how a vaccine protects you into the correct order.

• A vaccine puts dead/inactive pathogen into the body
• White blood cells make antibodies against its antigens
• Memory cells stay in the blood
• The real pathogen later invades
• Antibodies are made rapidly, destroying it before symptoms

Antibiotics vs painkillers

Two very different medicines: • **Antibiotics** (e.g. penicillin) **kill bacteria** inside the body, but do **nothing to viruses**. • **Painkillers** relieve **symptoms** but don't touch the pathogen. Overusing antibiotics breeds **resistant bacteria** (like MRSA): by **natural selection**, the few resistant bacteria survive and reproduce while the rest die, so the resistant strain spreads.

True of antibiotics?

Pick the TWO correct statements about antibiotics.

• They kill bacteria but have no effect on viruses
• Overusing them leads to resistant strains by natural selection
• They relieve pain without killing the pathogen
• They can cure viral diseases like measles

Prescribe or not?

You are advising a GP across three appointments. Use what you know about antibiotics and resistance.

• A patient has influenza, a viral infection, and asks for antibiotics. What do you advise?
• A patient with a bacterial infection feels better after three days of a seven-day course. What should they do?
• A resistant strain has spread through a hospital ward. What explains how it arose?

Order the drug trial

Put the stages of testing a new drug into the order they happen.

• Preclinical testing on cells and tissues
• Preclinical testing on animals
• Clinical trial on healthy volunteers, at low doses, checking safety
• Clinical trial on patients, finding the optimum dose

Before the exam

Trials use a **placebo** and are **double-blind**: neither doctor nor patient knows who got the real drug. Always name the **pathogen type AND example**; antibodies **mark and agglutinate** (they do not kill directly); the **secondary response** is faster and bigger; and antibiotic **resistance evolves by natural selection**.