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Pathogenesis: Definition & Example

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  • 0:03 Definition of Pathogenesis
  • 1:15 External Pathogenesis
  • 2:39 Internal Pathogenesis
  • 4:29 The Process of Pathogenesis
  • 5:54 Lesson Summary
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Lesson Transcript
Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, we'll learn about pathogenesis. We'll examine the steps that are involved and follow an example of going through the pathogenesis process.

Definition of Pathogenesis

All of a sudden your stomach doesn't feel so good. You run to the restroom and empty the contents of your stomach. For the next 12 hours you dare not wander too far from the bathroom because you know that this is going to continue for a while. You think about the chicken that you just ate and think 'I must not have cooked it enough, I knew it tasted funny'. Since you do get better within a day, and go back about your normal routine, you don't go to the doctor. If you had, you may have learned that it wasn't that chicken that got you sick, but instead it was the spinach that you had eaten 3 days prior. The process of how you get sick is called pathogenesis.

This process includes the pathogen that gets you sick, the method of how you got it, and what happened in the cells once it's in your body. There are many different kinds of pathogens, including bacteria, viruses, molds, and parasites. The methods of you getting these pathogens can be via contact, food, or air. What happens in the cells is varied and unique for each type of pathogen, even each individual person. The process to determine all of this is pathogenesis, and is often what researchers and doctors do in order to determine what needs to be done to fix the problem.

External Pathogenesis

In the previous example of a stomach flu, in order to determine the external pathogenesis, first the pathogen needs to be determined. This is typically done by running blood and other specimen tests. There are many tests that can be done in order to determine the type of pathogen. The two basic types are serotyping, which determines the type of pathogen (is it e-coli or is it salmonella) and genotyping, which determines the exact genome (or DNA) of that pathogen.

Now let's say after specimen testing of the stomach flu that you got the doctor determined that you had Escherichia Coli O157:H7. You also learn that there had been several other people recently who had reported having this same e-coli. The doctor starts asking what you have eaten. You promptly reply, chicken. But pathogenesis of e-coli actually takes several days after eating the food before you see symptoms of being sick. So you think back to several days before, and tell the doctor what you remember eating.

All of the foods (including where they came from) that those who had gotten sick consumed are compared. It is then discovered that everyone who had gotten sick had bought spinach from the same local vendor. They go and test the spinach from that farm and determine that the water used to irrigate that spinach had been contaminated with e-coli, causing the spinach to be a carrier of e-coli.

Internal Pathogenesis

So that's how they figure out what it is based on looking at external factors of where it came from, but how about using pathogenesis to look at what happens inside your cells? For this, we will look at another example.

In recent years' measles has been making a come-back in countries that had previously eliminated (or nearly eliminated) it. Since it is caused by a virus, the body becomes immune to measles after someone has become sick from it once. So it is different from e-coli (which is a bacteria) that can make you sick many times.

You can come into contact with a measles virus through the respiratory system or conjunctiva. In other words, you usually breathe in the measles virus. It doesn't immediately make you sick though, instead it starts to replicate in the inner lining of the respiratory tract. After about 10-12 days, you start to first feel sick. This primary illness is still in the respiratory system (lungs, nose, etc.). So you have a cough, sore throat, and runny nose. You will also get a fever, which can get as high as 105 degrees.

During this period the virus can invade other parts of the body, such as skin and organs, via the blood. After about 2-4 days a rash will start to appear, as your body attacks the measles virus in the skin. The rash usually starts at the hair line and works its way down.

After 5-6 days the body is typically able to fight off the virus. The rash disappears in the same order that it appeared. Although complications can occur, such as extremely high fevers, which can cause seizures. The infection in the lungs can also lead to pneumonia.

Since the symptoms of measles are fairly unique, a formal pathogenesis isn't typically performed to diagnose. Yet it is often performed in order to see where the virus came from in order to help stop the spread of the virus.

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