What’s Bugging You? A Short Guide to Viruses, Bacteria, Fungi & Other Microscopic Problems

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You’re hearing a lot about the coronavirus (COVID19) right now, and there is still that other virus to be worried about: flu. But just because those two infections are taking center stage, doesn’t meant that there aren’t other things that can cause an infection.

What else is out there that can bug you? Infectious organisms can be grouped as viruses, bacteria, fungi, and parasites. These infectious organisms are also called pathogens. Not all of these organisms, and there are millions of each type, cause disease. Most don’t cause a problem for human beings. Some bacteria and fungi are even beneficial. Think of the good bacteria in your gut that help with normal digestion or the fungi that are tasty mushrooms; the ones that give us blue cheese; or the yeasts that give us beer, wine, and bread.

Some types of disease can be caused by several different types of infectious organisms. Pneumonia can be viral, bacterial, or fungal in nature. Meningitis can be either viral or bacterial. A gastrointestinal disease can be viral, bacterial, or parasitic.


Viruses are very tiny infectious life forms that reproduce by attaching to a cell in the body and causing it to start making more copies of the virus. Some viruses kill the cell, and some cause the cell to change its function and can even cause it to become cancerous. Flu, the common cold, herpes, and chicken pox are some common diseases caused by viruses. Classes of virus include norovirus, which causes gastrointestinal disease; human papillomaviruses, which cause warts and genital cancers; and herpesviruses, which cause cold sores and chicken pox.

Antibiotics do not work against viruses, but there are antiviral drugs. Many viral infections are mild enough as not to be too noticeable. The body can often fight off a viral infection on its own. Others, like herpesviruses and human immunodeficiency virus (HIV) remain with you for life.


Bacteria are larger than viruses and are single-celled organisms. Bacteria can breed on their own and don’t have to depend on a person or animal’s cells to reproduce like viruses do. Your body is loaded with bacteria at all times, with most of them living benignly in your intestines or on your skin. Many of these are good bacteria that keep the bad bacteria from colonizing you.

Bacterial infections include cholera, tuberculosis, dysentery, and the bubonic plague. Ear infections, food poisoning, sinus infections, and eye infections are often caused by bacteria.

As with viruses, the body can fight off some bacterial infections on its own. The most common treatment for bacterial infections is antibiotics. However, because of overuse, many bacteria have become resistant to common antibiotics making them less effective or completely ineffective.


Fungal infections are caused by organisms that reproduce by emitting spores. Skin infections can be caused by fungal spores that land on the skin. Athlete’s foot and ringworm are examples of fungal infections of the skin. Fungal spores can also cause sinus infections and pneumonia. There are also fungal infections of the vagina, such as chlamydia. One type of fungal infection is thrush, which is caused by a fungal organism called candida.

There are antifungal drugs that can be used to treat these infections.


Parasites are bigger than bacteria or viruses. They can even be multicellular. Some parasites can only reproduce in a host organism, such as a human or animal, while others can reproduce on their own.

Parasites can be spread through contaminated food or water or can be spread through insect bites. Tapeworms and an organism called Giardia are parasites that can be found in contaminated water, while malaria can be spread by mosquito bites.

There are drugs available to treat many types of parasite infections.

How They Spread

Infectious organisms can spread in many ways. Viruses can be airborne and spread through sneezing and coughing. Some bacteria can spread through contaminated food or water. Others, such as sexually transmitted diseases, are spread by human contact or bodily fluids.

The first thing to remember is that the human immune system is very good at preventing infections or fighting them off if they start. The second thing is that most infections can be prevented or prevented from spreading by washing your hands regularly, covering your cough or sneeze, and taking other simple precautions.

Valerie DeBenedette
Valerie DeBenedette is an experienced health and medical writer who lives about an hour north of New York City with a dog that is smaller than her cat. Her work has appeared in magazines, newspapers, newsletters, and on websites. She is a member of the National Association of Science Writers.

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