Measles Information

Histoplasma capsulatum fungus, illustration
Histoplasma capsulatum fungus, illustration

What’s Making You Sick?

Viruses, Bacteria, Fungi and Parasites

They’re hiding in plain sight: on public transportation, in your kitchen, at your child’s day care center. There are four common types of pathogens, or germs, that can make you sick:

  • Viruses
  • Bacteria
  • Fungi
  • Parasites

Here, Michael P. Angarone, DO, Northwestern Medicine infectious disease specialist, explains each one.


  • Viruses are not living organisms. They’re pieces of genetic code (DNA or RNA) coated with protein.
  • Viruses invade your cells. Then, they use parts of your cells to replicate.
  • When replicated viruses are released in your body, they damage or destroy your cells, making you sick.
  • Antibiotic medications do not work against viruses. Some antiviral medications work against certain types of viruses.
  • Examples of diseases caused by viruses:


  • Bacteria are living, single-cell organisms.
  • Not all bacteria cause infections. You have more helpful bacteria in your digestive tract than cells in your entire body. These bacteria help with digestion, destroy harmful (pathogenic) bacteria and help control your immune system.
  • Pathogenic bacteria can make you sick by producing toxins and/or invading and damaging healthy cells.
  • Antibiotic medications can be used to treat many bacterial infections, but antibiotics don’t always work. Some types of bacteria may be resistant to them.
  • Examples of diseases caused by bacteria:


  • Fungi make up a group of microorganisms that includes mushrooms, yeasts and molds.
  • When fungi overgrow in or on your body, they can cause infection and make you sick.
  • Fungi are harder to treat, as they have thick walls that are hard to destroy.
  • Antifungal medications, either taken by mouth, intravenously, or applied to the skin, can eliminate fungal infections.
  • Examples of diseases caused by fungi:
    • Yeast infections
    • Athlete’s foot
    • Ringworm


  • Three types of parasites, or small organisms, can feed on your body:
    • Protozoa, which are single-celled organisms that live inside your body and feed on your cells
    • Helminths, or worms
    • Ectoparasites, which are organisms with multiple cells like ticks and mosquitoes that feed on your skin
  • Parasitic infections are more common in tropical regions of the world.
  • Antiparasitic, antibiotic and antifungal medications can be effective against parasitic infections.
  • Examples of diseases caused by parasites:
    • Malaria
    • Giardiasis
    • Intestinal worms

Protect Yourself Against Pathogens

Here are tips to help you avoid infection from pathogens.

To avoid infecting others, stay home when you are feeling sick.

The Last of Us: Could it Happen?
The Last of Us: Could it Happen?

Could the fungal pandemic in the HBO Max hit show "The Last of Us" really happen? Infectious Disease Specialist Michael P. Angarone, DO, weighs in.