The Differences Between Infection and Disease

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Preventing Disease: Normal Human Flora

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:08 Disease By Pathogen
  • 0:38 What Is an Infection
  • 1:35 What Is Disease?
  • 3:39 The Nuances of Disease
  • 4:49 Opportunistic Infections
  • 6:35 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will go over the differences between an infection and a disease. We'll cover everything from prions and infectivity to opportunistic infections and idiopathic disease. We'll also learn what the etiology of disease is and much more.

Disease by Pathogen

If you're a fan of ancient books or of Hollywood tales, then you've undoubtedly heard of something known as the Trojan horse. This was a device used by the Greeks to outwit the Trojans during the Trojan War. In a similar fashion, we'll discover in this lesson that any pathogen, or agent of disease, that is out to get you uses a sequence of events similar to the one the Greeks devised to destroy the city of Troy - except these pathogens are out to destroy your body instead of a city.

What Is an Infection?

When a pathogen enters its host and multiplies inside of it, we term that process an infection. A pathogen can be anything you can imagine, such as a virus, bacterium, fungus, parasite, or even a prion, which is an abnormally shaped protein that causes disease.

The entire process of infection can be likened to the men inside of the Trojan horse entering the city of Troy. When the horse enters the city, soldiers jump out of it, or multiply out of it, and infect the city. The ease by which an infectious agent can enter, survive, and multiply within a host is known as infectivity. In our case, because the soldiers inside the Trojan horse were carried into the city and easily survived and multiplied within it, they would be deemed 'highly infective.' However, the fun has only just begun at that point.

What Is Disease?

After the soldiers hidden away in the horse have multiplied out of it, so to speak, they run towards the city gates and open them up, thereby allowing the entire Greek army to come into the city. Once the soldiers of the Greek army run into the city, they begin to slaughter everyone and anyone that stands in their way. The people the Greeks kill are the citizens of Troy.

The citizens of the host city are like our own body's cells, tissues, and organs. They are being attacked and destroyed by the pathogen. When your own body's receptors, cells, tissues, or organs are damaged, destroyed, or inactivated, resulting in an abnormal state of function, health and overt clinical signs and symptoms, we term that process a disease.

There's only one catch here. Disease is a two-way street. The citizens of Troy don't just lay down their arms as the Greeks attack. They fight as hard as they can for their home, their city, and life. Likewise, our body has something known as an immune system, which fights off pathogens trying to freely multiply within our body. The problem is the immune system is sometimes not very picky in how it wages war.

You can liken our immune system, especially in the early stages of a disease, to the citizens of Troy showering fire arrows down upon the Greeks. While the fire arrows will certainly kill plenty of enemy soldiers, those same arrows can inadvertently strike a citizen of Troy or cause a building to catch fire. Basically, they cause destruction and mayhem on both sides of the war.

Likewise, inside of our own body, the immune system not only damages the invading pathogen but also our own body's cells, tissues, and organs. Therefore, our immune system contributes to the entire process of disease to a great extent. It's definitely not a perfect system by any means, as I am sure you can now clearly tell.

The Nuances of Disease

Now, before we move on to something else, I want you to look over the definition of disease one more time. Disease is when your own body's receptors, cells, tissues, or organs are damaged, destroyed, or inactivated, resulting in an abnormal state of function, health, and overt clinical signs and symptoms. There's something missing in that definition from the context of this lesson. Nowhere did I say that a disease must be caused by an infection.

I know for a fact you can think of at least one disease that doesn't have to be caused by a pathogen. The list is actually quite long, but here are some examples:

  • Diabetes
  • Cushing's disease
  • Heart disease
  • Cancer

And so on. Again, an infection is just one potential cause of disease but not the only one. In fact, sometimes we don't even know the root cause of a disease, or the etiology of it. Many times, a disease is idiopathic, meaning it's a disease that has no known cause.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account