Diseases Caused by Protists

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  • 0:00 Definition of Protists
  • 1:31 Malaria
  • 2:22 African Sleeping Sickness
  • 2:55 Chagas Disease
  • 3:18 Giardiasis
  • 3:45 Lesson Summary
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Lesson Transcript
Instructor: Terry Dunn

Terry has a master's degree in environmental communications and has taught in a variety of settings.

Protists cause some truly devastating human diseases, which is saying a lot for a microscopic, simple organism that often needs help from other organisms to reach its human targets. Here, you will learn about protists and the diseases they cause.

What are Protists?

Anyone who has gone, say, camping at Acadia National Park or hiking in the Everglades knows that there are plenty of dangers in the wild. Venomous snakes, large cats, and big insects come to mind. But really, it's the microscopic things that you have to watch out for--you can't see them coming and, if they get you, they can bring you to your knees. Protists are specialists at doing just that.

Protists fall into an odd category of the living world: not quite animals, plants, or fungi. Instead, they comprise a kingdom of their own called Protista. Protists are eukaryotes, which are single- or multi-celled living organisms, each of which contains a nucleus surrounded by a membrane. They look like something you might find on another planet. But it's their tiny size and simple physique that actually make protists stealthy enough to bring down a human.

The diseases that protists inflict on humans are caused by those that are parasitic--they feed on another organism, causing harm without benefiting their host. Often, parasites use another organism as a vehicle to gain access to the host. The go-betweens linking parasites and hosts are called vectors. The vector may not be harmful to the host, but it does help the parasite reach its target. Examples of common vectors for protists include mosquitoes, flies, and drinking water.

In the following sections, we'll discuss some of the more well-known diseases that protists cause, from malaria to giardia.


Probably one of the most feared protists in the world is the Plasmodium, and it causes malaria in Africa and South America. Each year, there are 300 to 500 million new cases of malaria, and the World Health Organization reports that this number could increase by 60% by 2050, in which case the number of malaria deaths would rise to as much as 5 million per year.

When a person is bitten by a mosquito (the vector), the protist first makes its way to the liver, then infects the red blood cells. That would be enough to harm a person, but there is one more step--the protist bursts from the red blood cells. This action destroys up to half of the body's red blood cells, causing anemia, followed by a high fever as the body tries to fight off the effects. Headache, vomiting, fatigue, and joint pain are also part of the package.

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