Pathogen

Pathogens are microorganisms that can make you sick. A microorganism is something that’s so small, you need a microscope to see it. Pathogens can cause illnesses like common colds, food poisoning, stomach bugs, tickborne illnesses, STIs — and almost anything else that you can catch from other people or from the environment around you. They’re commonly called germs.

Pathogens can infect people, animals and plants. Even pathogenic organisms, like bacteria and fungi, have their own pathogens. For instance, some antibiotics are made from fungi that kill bacteria.

Most pathogens only infect specific species, like one type of animal. But some can jump from one species to another, like from an animal to a human (zoonotic diseases). Bugs — like mosquitoes, ticks or fleas — can also spread some pathogens by biting you. When this happens, the bugs that spread them are called vectors.

Types

Types of pathogens include:

• Viruses: These are pieces of genetic information (RNA or DNA) in a shell (capsid). They use your cells’ machinery to make more copies of themselves.
• Bacteria: These are one-celled, living organisms. Many release toxins that make you sick.
• Fungi: Yeasts and molds are types of fungi that can infect you. They spread through the air and the environment in spores (reproductive parts).
• Parasites: These include protozoa and parasitic worms. They need another living thing (host) to survive.
• Prions: These are proteins that don’t work properly. When they infect you, they cause other proteins in your body to malfunction, too.

Some types of these organisms live on or inside your body without making you sick. They can even be helpful by protecting you from the harmful germs. Only the germs that hurt us are called pathogens.

Examples

There are thousands of human pathogens. Some examples of common ones include:

• Flu (influenza) viruses
• Norovirus (“stomach flu”)
• SARS-CoV2, the virus that causes COVID-19
• Group A Streptococcus, the bacteria that cause strep throat
• Salmonella, bacteria that can cause food poisoning
• E. coli, bacteria that can cause gastrointestinal and urinary tract infections
• Ringworm, fungi that cause athlete’s foot and jock itch
• Candida, fungi that cause yeast infections and thrush
• Giardia, a parasite that causes stomach cramps and diarrhea

How do pathogens infect your body?

Pathogens can enter your body through your mouth, nose or any other mucous membrane (part of your body that opens to the outside). They can also enter through cuts in your skin. Once inside your body, they reproduce (make more copies of themselves) and damage your cells. Some, like certain bacteria, also release toxins that make you sick.

You don’t always get sick when you’re exposed to a pathogen. Sometimes — especially if you’ve been infected with it already — your immune system can fight it off before you have noticeable symptoms.

How do pathogens spread?

Pathogens can spread through:

• Coughing and sneezing
• Close contact with another person, like cuddling, kissing or sex
• Shared utensils or cups
• Contaminated objects and surfaces, like doorknobs, phones and countertops
• Contact with poop, blood or other body fluids from an infected person or animal
• Bites from bugs or animals
• Contaminated or improperly prepared food or water
• Contaminated soil or sand
• Vertical transmission (from a pregnant mother to the fetus)
• Medical devices, like a bladder catheter or central venous line
• Medical procedures, like blood transfusions or surgery

What symptoms do pathogens cause?

The symptoms you get when a pathogen infects you depend on the type. Some common symptoms include:

• Fever
• Chills
• Runny or stuffy nose
• Cough
• Tiredness (fatigue)
• Muscle aches
• Headache
• Diarrhea
• Nausea and vomiting

How do you kill pathogens?

Washing your hands, disinfecting surfaces and safe food preparation (like cooking meats thoroughly) are usually the best ways to get rid of pathogens before they infect you. If you’re sick, your provider might prescribe medications to help get rid of them. Depending on the type of infection, these could include:

• Antibiotics
• Antivirals
• Antifungals
• Antiparasitics

Vaccines can also train your body to recognize specific pathogens so you can fight them off more easily if you’re exposed to them.