Protozoans are members of Kingdom Protista which exhibit animal-like characteristics. For instance protozoans are heterotrophs, which means they are unable to produce their own food, and they are all typically mobile using cilia, flagella, or pseudopodia. Of course, the main reason we are so interested in protozoans is because so many of them cause diseases in humans, especially in tropical environments.
Amebic dysentery is caused by the familiar genus Amoeba and is a result of the microorganism getting into the digestive tract from drinking water in which the organism is found. A person with amebic dysentery suffers from abdominal pain with diarrhea with blood and mucus. Another typically tropical disease is African sleeping sickness, which is caused by members of the genus Trypanosoma. The protozoan is usually transmitted by some insect, such as a tsetse fly, and lives in the blood stream of humans and many animals. In its advanced stages, the disease involves the central nervous system resulting in lethargy, convulsions, coma, and eventually death.
Of course, the most famous, or infamous, of all tropical diseases in malaria, which is caused by the genus Plasmodium. This organism, which is carried by the Anopheles mosquito, infects the blood stream and ruptures red blood cells. This causes cycles of chills and fever occurring at intervals that depend on the time required for development of the new generation of parasites. Throughout history, malaria was a major cause of death in humans. Until the summer of 1999, the United Nations’ World Health Organization (WHO) listed it as the disease that kills more humans than any other. Since that time, WHO has listed AIDS as the leading killer in the world. |
2002 McGraw-Hill Higher Education