Establishment of Disease: Entry, Dose & Virulence

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: What Are Viruses? - Definition, Structure & Function

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

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:05 Disease Due to an Infection
  • 0:27 Pathogenicity
  • 2:03 Virulence, Lethal…
  • 4:08 Entry into a Host
  • 5:26 Lesson Summary
Add to Add to Add to

Want to watch this again later?

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

Login or Sign up


Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Artem Cheprasov
This lesson will delve into what predisposes an individual to get sick. We'll talk about things like the entry, dose, and virulence of a pathogen and how they play a role in the establishment of a disease.

Disease Due to an Infection

I hope that you are over 21, because we will have to enter a casino to get some of the points in this lesson across. If you're not, then maybe you can borrow a fake ID or don a fake beard to get in. This lesson will be discussing how it is that you may get a disease due to a few key factors involved in the process of infection.


To clarify, an infection is the first step in the establishment of disease. If you don't get infected by a pathogenic organism, then you won't get sick unless, of course, you get sick due to a non-infectious disease process, such as diabetes. However, this lesson will focus in on how infectious causes establish a disease at the very onset of the entire process.

There are several things that influence how well-suited a microbe is to causing a disease. The ability of a microbe to cause disease is termed pathogenicity. This is a qualitative description. For example, some microbes are pathogenic, meaning they can harm you and cause you a disease. They're like the alcoholic drinks at the casino that will end up hurting you the morning after you drink them. This is in contrast to non-pathogenic microbes that will not cause you any harm. This is akin to the non-alcoholic drinks that you may encounter at a casino.

Again, pathogenicity is a qualitative term and a relative one as well. For example, in a normal healthy person, certain microbes may be considered to be non-pathogenic - that is to say they are unable to cause a disease in that person. But, if a person is immunocompromised due to some other infection, notably HIV, even what was at one point considered to be a non-pathogenic microbe can now cause a disease in a person that is immunocompromised.

Virulence, Lethal Dose, and Infectious Dose

While pathogenicity is a qualitative term, there is a more quantitative term that is sometimes used. This term is known as virulence, and it is the degree of pathogenicity of a microbe. It's essentially a measurement of a microbe's disease-producing potential. You can liken virulence to the odds of winning a certain game at the casino. The more virulent an organism is, the higher the chances are that you'll get a nasty disease due to that specific microbe.

Virulence is sometimes measured quantitatively by a term known as LD50 or lethal dose, 50%. This is the number of microbes necessary to kill 50% of a population infected with that microbe. The lower the LD50, the more virulent something is. That's because we need a smaller dose, or a smaller number of microbes, to kill a set number of individuals.

For instance, you know that cyanide is really poisonous or virulent, so to speak, when compared to something like sugar. Therefore, if you were to give a test population of 1,000 people either sugar or cyanide to try and kill 50% of them, you would need them to eat far more sugar than cyanide to kill 50% of the sample population. Therefore, the LD50 of cyanide is far lower than the LD50 of sugar.

Virulence can also be measured by something known as ID50 or infectious dose, 50%. This is the number of microbes necessary to infect a host in 50% of a sample population. Again, the lower the infectious dose, the more virulent a pathogen is since we need fewer amounts of that pathogen to cause an infection in the host.

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 160 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