Protists are single-celled organisms that spread disease, either through direct infection or via toxins excreted into food and water supplies. Protist infections cause gastrointestinal and nervous system diseases, as well as skin and lung conditions.
Amoebas are protists that cause a range of human diseases. They are responsible for amoebic dysentery, which causes serious diarrhea, and for a fatal form of encephalitis. Amoebas can also form lesions on the eyes and skin, leading to further infection or blindness.
Dinoflagellates are protists that cause Red Tide, a form of water pollution. They deplete ocean water of oxygen, creating dead zones that cannot sustain animal life. Dinoflagellates also release a toxin that kills fish. The fish that do survive accumulate the toxin in their flesh, causing nausea, vomiting and neurological symptoms in humans who consume them. Dinoflagellate toxicity in humans is referred to as ciguatera or shellfish poisoning.
Protists also cause African sleeping sickness and Chagas disease, two related illnesses that occur on different continents. These protists are both from the genus Trypanosoma and spread to humans through insect bites. African sleeping sickness is endemic to the western and central parts of Africa, while Chagas disease occurs in Central and South America.