What can we do to prevent outbreaks of infectious diseases from becoming epidemics or pandemic? In this course, you’ll learn the facts about infectious diseases and medical responses. We'll focus on the public health laws and policies that provide the framework for effective prevention, like quarantine laws, drug development policies, and bioterrorism and biodefense.
Week 2 Video 1: What causes infection? What is an infectious disease?
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From the course by University of Pittsburgh
Epidemics, Pandemics and Outbreaks
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From the lesson
Week 2: Understanding Infectious Diseases
Welcome to Week Two! This week’s lesson provides you with the tools needed to understand the world of infectious disease. It will allow you to develop a context of knowledge and familiarity with the concepts that inform legal and public health response strategies to outbreaks, epidemics and pandemics. What you learn here will be drawn upon in weeks 3-4: “Global Health Security” and “Local Countermeasures.”
Meet the Instructors
Elena A. BaylisAssociate Professor
Law
Elizabeth Ferrell Bjerke, JDDirector, JD/MPH Program
Health Policy and Management
Amesh A. Adalja, MD, FACPSenior Associate
UPMC Center for Health Security
Ryan MorhardGuest Instructor
[MUSIC]
Hi, this is Dr. Amesh Adalja, one of the instructors for this course.
I'm an infectious disease physician,
and in this video, we're going to talk about what causes an infection and
what the basis is for the concept of infectious diseases.
So to understand infectious diseases,
we have to take you back in history to understand the origins of all diseases.
You probably heard about the four elements that were known in the ancient world,
earth, fire, water and air.
Well they had counterparts in the medical world.
And initially diseases were thought to be caused by evil spirits or
a divine intervention.
But it was a major advance, and it might not sound like a very major advance,
when they started thinking about the four humors,
blood, phlegm, black bile, and yellow bile.
These things are really irrelevant now, but
that's how people understood the cause of disease in the ancient world.
And what they thought disease was,
was when one of those humors went out of balance.
So maybe you had too much blood, maybe you had too much phlegm.
And that's why you heard about things like blood letting, and that's why that was
common, because they were trying to restore the balance of the humors.
And that's what really held sway for a long time in medicine.
Eventually people started thinking that maybe there are external causes.
And one of the external causes that they thought about was something called
a miasma.
So that's just kind of like a piece of evil air that can cause disease and
it kind of gives the root to what we would call malaria, or mal air, or bad air, and
that's what people thought.
But really the revolution in all of medicine, and particularly in infectious
decease, was the germ theory of disease, which you may have heard about.
And that's really what forms the basis for
how we think about infectious diseases today.
There was some early hypotheses about it that maybe these invisible germs
were causing infections, but it really didn't take off until the microscope was
improved to a point where people could actually see these things with their eye.
Because you couldn't see them with the naked eye and
it was very unheard of to think something so small could kill a human.
Some major people there are Antonie Leeuwenhoek who, who lived in,
in The Netherlands and grinded lenses with such
precision that he was able to see things that nobody could see before.
We also had Louis Pasteur, who you've all heard about, and
you think about pasteurization of milk, it comes from him.
When he, what his major contro, contribution,
the first one was that he realized that certain diseases of wine and
alcohol were caused by bacteria and yeast fermenting things.
So that was the idea that microorganisms could cause changes in things.
And that revolutionized the way people thought about industry and disease.
He also looked at diseases of silk worm and found that they were caused by
infection and changed, and changed the, the face of of me, of medicine eventually.
But there was a big gap because he was a scientist, he wasn't a physician.
However somebody named Joseph Lister,
who you might have heard about because of Listerine is named in, in honor of him,
took Louis Pasteur's ideas about the germ theory of disease, and
applied them in a hospital thinking how are we going to sanitize things?
How are we going to sterilize things in order to prevent infections from
taking hold?
Another person is na, is named Ignaz Semmelweis.
You probably didn't hear about him, but
that's the person that really got doctors to start washing their hands,
because he realized germs carried on people's hands were causing diseases.
Eventually Louis Pasteur discovered things like the rabies vaccine, the,
the cause of anthrax, along with Robert Koch in Germany.
They were kind of rivals and those two,
Pasteur and Koch, really pushed infectious disease into the, into the future and
actually modernized it, and we still use all of their findings today.
So one distinction I want to make is, I'm talking about infectious diseases and
there's another term called contagious disease.
And this came up a lot in the Ebola outbreak on the news with media people
confusing the two.
An infectious disease just means the disease is caused by a microorganism.
And in another video I'll talk to you about the different types of
microorganisms.
A contagious disease is a disease that can be spread from one person to another.
So something like influenza is a contagious disease,
where one person has it, they spread it to another person.
Whereas a disease like tetanus, where you get your tetanus shots for, that isn't,
that's an infectious disease, it's a bacteria cau, elaborating a toxin that
causes you to get sick, but you can't spread that to anybody else.
So there's a big distinction between what's infectious and what's contagious.
In a lot of our control measures when you, when you have these lectures on
isolation and quarantine, that's going to be a major point.
Is this disease a contagious disease that poses a risk to others,
that needs to have special legal provisions enacted?
Or is this an infectious disease that is not communicable?
So we're going to talk now about the different types of microorganisms
that can cause a disease.
And remember, these couldn't be seen by the naked eye and that's why this
whole field really only started with the advent of, of good microscopes.
So we've got bacteria.
Most people have heard about bacteria.
They are single celled organisms.
They are all over the world.
The, the, the world has more bacteria in it than any other organism,
even in yourself, in a human, you have more bacterial cells than human cells.
And we talk about those bacterial cells as your microbiome,
which you might have heard about.
That's the makeup of all the different bacteria in your body, and
they interact with your immune system, and they're really essential for life.
Fungus, you've heard of that.
You see it in, in foot fungus people have toenail fungus.
That's, that's another type of microorganism that can cause disease.
Protozoa, things like malaria, things that,
that cause that can cause infections.
Bigger things which you actually can see in some stages by the naked eye are,
are worms.
So things like hookworm, tapeworm.
Viruses, we talked about influenza briefly earlier.
That, those are very small.
They are something that are not really alive, they're really just protein and
genetic material.
And they are not really considered alive because they have to depend upon a,
on a host to do all of their metabolic work in order to reproduce themselves.
And there's something, it's kind of an advanced topic, called a prion.
That stands for proteinaceous, infectious material, and
that's a protein that can cause disease.
The prototypical example of that is mad cow disease.
And this really threw the scientific dogma on its head because we didn't
think that we could have an infectious particle without genetic material there.
But a protein itself proved to be infectious and
it led to the Nobel Prize in, in 1997.
So let's think about the treatment for infectious diseases.
So in the early 1900s, even when we knew these microorganisms were causing disease,
there wasn't much to do.
You could give people some supportive care, but we didn't have anything.
The big breakthrough came when people started thinking about dyes.
It, it might sound, might, might sound odd that,
how did dyes have to do with infectious disease treatment?
But dyes were used to stain things, and they started using them and medicine.
And they realized that certain dyes could st,
could stain certain tissues differently.
And there was a specific uptake, this tissue would take up this dye,
this one would take up another dye.
And the idea arose, maybe bacteria could be targeted with specific dyes.
So that's really how the first antibiotics and
antibacterials came about, was looking for dyes that could kill bacteria.
And those were our sulfa drugs.
You might have heard of the drug Bactrim, that is a sulfa drug, and
its progenitors were, were identified using dye studies.
Also arsenic, which was used for syphilis, also arose out of this dye industry.
But really most people think about the,
the dawn of our control of infectious disease with the discovery of penicillin.
It's a very interesting story, and it centers on a man named Alexander Fleming
who was a British scientist who was, was very, very famous.
And what he did is, he had a, a dish of mold, and he left for the weekend,
this is a very famous story, and came back and he looked at that mold.
And, and he realized that that mold had antibacterial properties because some of
the, some of the bacteria had been killed by the, by the effects of that mold.
And that's how he discovered penicillin.
However he didn't put it into action.
He realized that this happened, he published about it, but
he didn't actually take the next step into trying it in human infections.
That was left to, to Howard Florey and Ernst Chain.
And all three of them together won the Nobel Prize.
They actually commercialized penicillin, showed how it could work, and it really
changed the whole way that everybody thought about infectious diseases.
People weren't dying from simple infections any more.
Remember, George Washington died probably from a strep throat infection.
And that was our first antibiotic, penicillin.
And in, since that time we've had scores of antibiotics.
It's important, you may have heard about the,
the phenomenon of antibiotic resistance,
where bacteria develop tools to resist antibiotics so that they don't kill them.
This is something that Alexander Fleming warned about in his Nobel Prize winning
lecture saying, if you use antibiotics injudiciously,
if you use them inappropriately, when you don't need them, for viral infections.
because remember, antibiotics, we're talking about antibacterial agents,
these only work on bacteria, bacteria will become resistant to them.
And we are now reaping all of that now when we see
rising rates of antibiotic resistance.
Similar stories are, exist for antifungals, for, for fungal, for
fungal infections, antivirals for
viral infections, anti-worm diseases for, anti-worms for, for worms.
And some of these drugs are still, all this discovery is still ongoing.
We are still trying to make new antibiotics, new antivirals.
And during the Ebola outbreak you may have seen certain drugs like ZMapp used.
These are experimental drugs that were pushed out to the public
because of the emergency here.
And, and you'll hear somewhat about the, the provisions in law that allow
experimental treatments to be used, such as emergency use authorizations.
The other thing that I wanted to talk about is vac, are vaccines.
These are routine.
People have really benefited tremendously from vaccines.
It's probably one of the things that's responsible for our lifespan gains,
one of the biggest things that's responsible for our lifespan gains.
But the first vaccine was for smallpox, and this is a really interesting story.
There was a man named Edward Jenner who noticed that women who were milk
maids would get cowpox, but were then immune from smallpox.
So before that what people would do to try to protect from smallpox was give people
a little dab of smallpox on their skin
to protect them because they were getting it in a, in a very low dose.
But that had a lot of side effects.
People died, it could spread smallpox.
That was called virialation.
So what they move, what, what Jenner thought to do was,
why don't I take some cowpox and give that to somebody and
then see if they're protected against smallpox, and it, and it was.
And this was a, a major breakthrough.
Edward Jenner was credited with making the first vaccine.
We actually have now eradicated smallpox from the planet, using the Jenner vaccine.
The whole wor, the word vaccine comes from the, the Latin word for cow.
So in honor of Jenner, we call all vaccines, vaccines.
The next vaccine you really think about is the rabies vaccine,
which was developed by Louis Pasture, which was really a, a breakthrough.
because he actually started to understand why a vaccine works.
And what, what he was doing was taking rabies and
weakening it, and then injecting it into people.
Because the immune system could respond to the weakened version and
make antibodies or make protective them,
have the protective ability to fight off the virus the next time and so on.
And then, when you were exposed to the full-blown rabies, it couldn't do anything
to you because your immune system was primed and ready to fight.
And that was the second vaccine.
Right now we have a whole host of childhood vaccines that you probably have
heard of and you have benefited from.
And one of the dangers is, is that we've become complacent, because people are so
used to living in an era without infectious diseases.
We have the rise of the anti-vaccine movement,
which really started all the way back with Edward Jenner.
People refused vaccination back then.
So that's really something that we, you have to keep in mind.
And infectious diseases may seem to be under control, but
they're only a moment away, and we do live in a world of microorganisms.
[MUSIC]
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