Pathogens and the environment| AP Environmental science| Khan Academy

In this video, we're going to be talking about pathogens and how an environment might help or hurt the spread of a pathogen. So first of all, let's make sure we know what a pathogen is. "Patho" comes from Greek "pathos," which is referring to disease. "Gen," you might recognize that part of the word from words like generate or genetics, it means to produce. So, a pathogen is something that produces disease.

Now, a good example of a pathogen that we're still facing on our planet is malaria. Malaria is a very, very unpleasant disease. It involves the attack on red blood cells. It causes fever, chills, sweats, severe abdominal pain, vomiting, headaches. It can make you more susceptible to other diseases, and if it's not treated, it can kill someone.

Now, the pathogen that creates, or that produces malaria, that causes the disease malaria is known as Plasmodium falciparum. And this right over here is a picture of it attacking red blood cells. We see healthy red blood cells right over here, and then the ones that are in this deep color, this is being attacked by the malaria pathogen. As it does that, it destroys those red blood cells and it leads to all the symptoms that I talked about.

So let's think a little bit about the environment in which malaria is likely to be spread. Well, there's a few things that we know. We know that the malaria pathogen can only operate, can only go through its full life cycle in relatively warm conditions. It needs to be greater than 20 degrees Celsius, which is the same thing as 68 degrees Fahrenheit. We also know that it is spread through mosquitoes, in particular this mosquito right over here, the Anopheles mosquito.

Mosquitoes are unpleasant even when they aren't zoomed in like this, but this is actually quite frightening. We all know what mosquitoes like to do, at least to human beings; they drink our blood. You need an environment where both mosquitoes can thrive, and there are a lot of human hosts whose blood they can drink, and where they can spread the malaria pathogen from one host to another. Ideally, you'd like a high population density, and for the mosquito spread, you definitely want a hot and humid environment.

So you might guess that if you're looking for things that don't dip below this, because if you dip below this, the malaria pathogen is not going to be able to go through its life cycle, you're likely looking at regions in the equator. This map right over here confirms our intuition. What you see in these orange regions are where you see the highest prevalence of malaria. The yellow regions are where you might see malaria but not as high of a prevalence. The blue areas are where you don't see malaria.

As we guessed, if you look generally at where the equator is, that is where you're likely to see malaria because it is warmer there; you don't see temperatures dip. You also see hot, humid environments in Sub-Saharan Africa. The Sahara Desert is roughly right over there, and that is very dry—not good for mosquitoes. But if you look at Sub-Sahara right below this, you have a high prevalence of malaria.

Now, one not so comforting realization is as the Earth warms, you're going to have more regions that are not just tropical regions, not just equatorial regions, that are going to be suitable for the spread of malaria. So easily, you could have what are traditionally subtropical environments or even temperate environments that, if it gets warm and hot and humid enough, you might see the spread of malaria over time.

Malaria and the malaria pathogen aren't the only things that might spread. You have things like the Zika virus, which is a virus—not a protist in the case of malaria—but a virus that's also spread by mosquitoes. So it also thrives wherever mosquitoes might be able to thrive. The warming, more humid environment isn't just going to support the spread of mosquitoes; it could support the spread of other pathogens like bacteria, which could cause diseases like cholera, which is caused by infected water.

So I'll leave you there. I like to be a little bit more upbeat about things, but it's just good to realize that this is out there, and as our environment changes, it's not just the environment effect that it affects, but it could also affect the spread of disease.