What Is a Pathogen? – Types of Infections and How to Prevent Them

Pathogens are organisms (microbes) that cause diseases. There are many microbes in every living organism, but they are not automatically pathogens. They can affect you if your immune system is weak, or microbes invade a vulnerable part of your body.

All living things are affected by pathogens. Even bacteria are affected by viruses called phages. They can be transmitted in many ways – through air, touch, bodily fluids (blood, sexual intercourse, feces, orally).

To find out more about what is a pathogen?, which types of pathogens exist, and how to prevent them – read this article.

Types of Pathogens

There are an astonishing number of pathogens in the world. However, just a tiny number of them affect humans. For example, a liter of seawater has 10 billion bacteria and more than 100 billion viruses. But only one in a billion of these microbes is a human pathogen.

About 1,400 human pathogens have been found and described. Although classifiable in several small groups, there are four major types of pathogens: viruses, bacteria, fungi, and parasites.


Viruses are made up of pieces of RNK and DNK and coated with protein. They need a living host to multiply and grow. The living host can be anything from bacteria to the human body.

The virus will infiltrate the living organism and occupy a cell. From there the virus replicates and spreads to other cells, killing the infected cell in the process.

There are instances in which viruses remain dormant for a period of time, which causes an infected person to appear healthy and recovered, only for them to get sick again.

Viruses can be mild, seasonal illnesses like cold or stomach flu. However, they can be much severe and even fatal, especially if not treated in time. The most dangerous common viruses include human immunodeficiency virus (HIV) and hepatitis C.


Bacteria are one-cell organisms that are not always dangerous to other living things. They come in a wide range of shapes and sizes (rods, spheres, spirals), and can thrive in almost any environment. In fact, you have almost 30 trillion bacteria in your body at any time – the majority of them in the gut.

As not all bacteria cause diseases, they are not all pathogens. The dangerous forms are called pathogen bacteria and they usually become harmful when your body is already infected by a virus. Viral infections weaken your immune system and turn harmless bacteria into pathogenic bacteria.

Some examples of bacterial infections are meningitis, strep throat, or food poisoning. You treat these infections with antibiotics, though some bacteria become resistant to antibiotics over time. This makes them harder to treat and happens either due to evolution or extensive use of antibiotics.


Fungi are much larger than bacteria and viruses and can be found almost anywhere around you. They grow indoors, outdoors, even on human skin. They thrive in wetter surroundings, and if they grow big enough can cause infections.

There are more than a million known fungi in the world, but only about 300 can be pathogenic. Their cells are thicker due to the cell wall and membrane that protects its components. Because of that, they are much harder to kill than bacteria or viruses.

Mushrooms, yeast, and mold are all types of fungi that can harm the human body. Some of the fungal infections include histoplasmosis, ringworm, and vaginal yeast infections. In recent years, new strains of fungal pathogens appeared, such as Candida auris. They are believed to be much more dangerous than previous infections.


Parasites are usually the largest of all pathogens. They are tiny animals that infiltrate another living organism and feed at the expense of its host. Over time, the host will become ill. In some extreme cases, this can even be fatal.

Parasitic pathogens are most common in the subtropical and tropical areas, but they can, in fact, occur anywhere. The usual parasitic infections are tapeworm (affects the digestive tract), protozoa (a single-cell organism that reproduces inside the host), ticks (causing Lyme disease), helminths (worms), plasmodium, and ectoparasites (larger organisms that live on your skin).

You can get infected by a parasitic pathogen in many different ways. If the water or food is contaminated, the parasite can infiltrate your body. The same goes for contaminated blood or soil. There’s also a chance to catch a parasite through sexual intercourse, or through insect bites.

How to Protect Against Pathogens

Now that you know what a pathogen is, the question remains – how to prevent the infection? Some of the methods to avoid infections are well-known. Here they are:

  • Get vaccinated.
  • Wash your hands whenever you can, especially before meals.
  • Avoid sharing items for personal hygiene with others, especially a toothbrush or razor.
  • Prepare and cook your food well to prevent parasitic infection. Also, make sure to always store sensitive food (meat, eggs, etc.) properly.
  • If you’re feeling unwell, stay at home. Don’t go outside if you have a flu – vomiting, diarrhea, fever, etc.
  • Protect your skin from insects and insect bites.
  • Always have safe sex.
  • Don’t share glasses, cups, or kitchen utensils.
  • When you travel, especially cross-continent, learn about health risks and potential prevention. Some tropical countries require you to get vaccinated before you enter.

Modern medicine has a wide range of methods to fight pathogens, whether viruses and bacteria, or fungi and parasites.

Your body already has various mechanisms to fight off the pathogens on its own. Some of your cells such as antibodies, neutrophils, and leukocytes are specially created for that purpose.

Also, some symptoms of flu or illness are actually a sign that your body is fighting off these harmful microbes. Sneezing, coughing, and fever are all methods that your body uses to remove or kill the pathogens.

A Well-Contained Threat

The increased mobility of people worldwide due to globalization presents medicine with new challenges. Outbreaks of viruses can happen easily and quickly become a severe health threat. Also, infectious diseases are still a major threat, responsible for a quarter of all deaths.

Although pathogens can still be dangerous and severe, the situation seems much more positive than it was a century ago. The pathogens that were fatal for millions of people such as plague, tuberculosis, or smallpox have now almost been completely eradicated. In that respect, there’s a lot to look forward to in the future.