Pathogens vs Hosts: The Tiny Invaders and Their Targets
In 1918, a flu swept across the whole world in less than a year. The germ that caused it was so tiny that 500 of them could line up across the width of a single human hair. That tiny germ is called a pathogen. The person it made sick is called the host. Every sickness you have ever had was a contest between a pathogen and a host — and that host was you. Epidemiologists (say it: EP-ih-dee-mee-OL-oh-jists) are scientists who study how pathogens move from host to host. To do their job, they have to know the difference between the two, because you fight a germ very differently than you protect a person.
What You'll Learn
• What a pathogen is and the four main kinds: viruses, bacteria, fungi, and parasites • What a host is and why some hosts get sicker than others • How a pathogen travels from one host to the next • How your body acts like a castle with guards to keep pathogens out
Pathogens: The Uninvited Guests
A pathogen is any living thing (or almost-living thing) so small it can only be seen with a microscope, and its 'job' is to grow inside a host. There are four big families: Viruses — the smallest. The common cold and the flu are viruses. A virus cannot grow on its own; it must sneak inside your cells. Bacteria — bigger than viruses. Strep throat is caused by bacteria. Not all bacteria are bad; some live in your tummy and help you digest food! Fungi — like tiny molds. Athlete's foot is a fungus that likes warm, damp sneakers. Parasites — such as the germ that causes malaria, carried by mosquitoes.
Hosts: Where Pathogens Live
A host is the living thing a pathogen invades. You can be a host. So can a dog, a bird, or even a plant. Sometimes a host feels sick, and sometimes a host carries a pathogen without feeling sick at all — that person is called a carrier, and they can still pass the germ along. Why do some hosts get sicker than others? Because everybody's body defenses are a little different. A person who is rested, well-fed, and has had their shots has stronger guards than someone who is tired and hungry.
Washing your hands with soap for 20 seconds — about as long as singing 'Happy Birthday' twice — washes pathogens down the drain before they reach a host. It is the single best thing a kid can do to break the chain.
How Pathogens Travel
A pathogen needs a way to get from one host to the next. This is called transmission. A cough or sneeze can launch droplets over 6 feet. Touching a doorknob and then your eyes can carry germs on your hands. A mosquito bite can inject a pathogen straight into your blood. Epidemiologists draw maps of these paths to figure out how to stop an outbreak.
Match each pathogen to the sickness it causes.
Terms
Definitions
Drag terms onto their definitions, or click a term then click a definition to match.
What is the difference between a pathogen and a host?
Why can a 'carrier' be dangerous even though they feel fine?
Build a Germ-Spread Chain
Get 5 sticky notes. Write 'Patient 0' on the first. On the next four, write the names of people Patient 0 might touch in a day (family, friend, teacher, teammate). Lay them out and draw arrows showing how a germ could hop from one to the next. Then circle ONE arrow and write how you could break it (wash hands, cover a cough, stay home). Show your chain to someone and explain the one place you'd stop the germ.
Flashcards — click each card to reveal the answer
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