Infectious a ride, you have officially become an

Infectious agents are tricky little invaders. They sneak in, use your body, and often make you sick in the process.

In this lesson, you will learn about the different types as well as some common examples of each.

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What Are Infectious Agents?

An infectious agent is something that infiltrates another living thing, like you. When an infectious agent hitches a ride, you have officially become an infected host. There are four main classes of infectious agents: bacteria, viruses, fungi, and parasites.

This fab four can infect all sorts of living things.


Bacteria are single-celled organisms without a nucleus. It may seem like they are simple critters, but bacteria have tons of characteristics, and they are very diverse. They can vary in shape, size, structure, and even the environments they are built for.

Because bacteria come in so many flavors, they are found in all sorts of places from the deepest underwater caves to the food in your lunchbox.They are even on you and inside of you at all times. In fact, your intestine has a permanent infection. But, don’t worry, these gut bacteria are actually very helpful for digestion.

Many people take probiotic supplements to encourage the growth of this group of healthy bacteria.If a pro-biotic is meant to be pro-bacteria, then what do you think an anti-biotic does? Yep, an antibiotic is harmful to bacteria. Doctors prescribe antibiotics to help your immune system out when you have a bacterial infection.Bacteria can cause different symptoms depending on which bug is involved (bacteria are sometimes called bugs even though they are not insects). Some examples of bacterial infections are strep throat, tuberculosis, E.

coli, anthrax, salmonella, syphilis, and bubonic plague.


Another type of infectious agent is a virus. They are even tinier than bacteria.

A virus isn’t technically alive because it cannot function unless it has a host. On their own, they are just little packages of a DNA or RNA genome inside a protein shell called a capsid. Their favorite and only activity is to hang around in an ‘off’ position and wait.If they get inside a host, they will whir into action. Their only goal is to hijack the host cell’s machinery and replicate themselves.

This can occur right away or they might lay dormant for a bit before they replicate. After new viruses have been made, they go out into the world and the cycle starts over.Like a bacterial infection, a viral infection can have different symptoms depending on which virus is doing the infecting.

Some examples of viral infections are the common cold, the flu, rabies, ebola, herpes, HIV, HPV, and hepatitis.


The third type of infectious agents are fungi. Fungi are multi-cellular or single celled organisms with a nucleus and organelles, but they are unique from plants or animals. Fungi like to feed by absorbing nutrients from their surroundings. Yeast and mushrooms are types of fungi. Most types of fungi are not dangerous, but there are some that can infect humans and cause trouble.

Often a fungal infection affects the skin and causes a minor rash, but other fungi can also cause more serious problems, like a lung infection or a blood infection.There are about 300 fungi that are known to make people sick. Some types of fungal infections affecting humans are athlete’s foot, a vaginal yeast infection, ringworm, and aspergillosis.


Parasites are organisms that like to live off of other things. Parasites can be broken down into two classes: protozoa and helminths (worms).

Neither is an ideal roommate to share your body with.Protozoa are single celled organisms, but they are not quite like bacteria. They are small, but they can still cause serious problems during an infection when they multiply. Malaria is one of the worst parasites.

It’s transmitted to humans by mosquitoes. Worldwide, over half a million people were estimated to have died from Malaria in 2010. Amoeba infections are also parasitic protozoa infections; some species even specifically infect your brain.Helminth worms are multicellular and can often get quite large. Worms notoriously infect the digestive tract of untreated dogs and cats, but they can also infect humans. Ascaris, flatworms, and whipworms are the three common types of worms. They are each estimated to currently infect at least half a billion people, mostly in Africa.

Lesson Summary

Infectious agents are all around us. They like to find a host and use the host’s resources for their own benefit. All sorts of living things can be infected, including you. The symptoms of an infection depend entirely on the host and what they were infected with. The four classes are bacteria, viruses, fungi, and parasites.

These guys are mostly microscopic, so your best bet to avoid them is to cook your food, wash your hands, cover your cough, and cross your fingers.


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