Harmful Protists: Definition, Effects & Examples

Harmful Protists: Definition, Effects & Examples
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  • 0:02 What Are Protists?
  • 0:43 Examples of Hamful Protists
  • 4:26 Lesson Summary
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Lesson Transcript
Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Protists are tiny organisms that are found all around us, even if we aren't aware they are there. Complete this lesson to learn about some of the harmful protists that exist and the effects they can have on humans.

What Are Protists?

Before we dive into the world of harmful protists, let's look at the group as a whole. Although protists are a pretty diverse set of organisms, all are eukaryotic, meaning they have a defined nucleus enclosed within a membrane. Most are microscopic and live in aquatic or damp environments, and there are more unicellular protists than multicellular ones.

We can further classify protists based on their characteristics: plant-like, animal-like, or fungi-like. Some protists are autotrophs, which means they are capable of making their own food, while others are heterotrophs, which means they have to eat other organisms to survive.

Examples of Harmful Protists

Don't let the title of the lesson mislead you: Protists provide many benefits. They produce almost half of the world's oxygen supply; they are an important part of the food web; and they have been used in medical and industrial research.

But, like any other organism, they can also inflict harm, particularly to humans. Most harmful protists are classified as animal-like protists that act as parasites, or organisms that benefit from causing harm to other organisms. Let's take a look at some examples.

Malaria is caused by plasmodium, a protist that uses mosquitoes as an intermittent host before infecting humans. Once a human is infected with malaria, common symptoms include fever, chills, sweating, headaches, nausea, vomiting, and body aches. Very severe cases of this disease can cause organ failure and blood abnormalities. There is no cure for malaria, although there are vaccinations that can be given before exposure.

African sleeping sickness is caused by trypanosoma protists. As the name implies, this disease is most common in Africa as a result of the continent's abundance of tsetse flies that transmit the disease. Both humans and domestic animals can be infected, and early stages of infection cause fever, headaches, joint pain, and itching. As the infection progresses and becomes more severe, additional symptoms develop, including confusion, poor coordination, sleep disturbances, and unusual behavior. Most cases are fatal, although in a few instances, non-symptomatic carriers have been identified.

Giardiasis is caused by giardia protists. Humans consume them by eating or drinking food or water contaminated by fecal material. Giardia can survive common disinfection methods, and infected humans might experience diarrhea, gas, stomach cramping, nausea, vomiting, and dehydration. Sometimes symptoms also include eye and skin irritation. Medication is available to treat giardiasis.

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