Such diseases as African sleeping sickness and Chagas disease are caused by members of the genus Trypanosoma.
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In an older system of classification, the genus Trypanosoma belonged to the phylum Protozoa and the class Flagellata. They were protozoans because they were one-celled animals; they were flagellates because of a whip-like structure called a flagellum, which they used for locomotion.
Trypanosoma brucei is the pathogen responsible for African sleeping sickness. At the onset of this disease, the patient may suffer such symptoms as fever, headache, and swelling of the lymph nodes. Eventually, when the pathogen enters the nervous system, the patient does exactly what the name of the disease implies. He sleeps a lot, eventually becoming comatose.
The internal anatomy of Trypanosoma resembles other cells in many ways. It has a nucleus, Golgi apparatus, endoplasmic reticulum, and a basal body at the foot of the flagellum. Trypanosomes also have a special structure: a large elongated mitochondrion associated with a kinetoplast.. The kinetoplast is a portion of the mitochondrion that has many rings of DNA linked together. This unusual structure replicates independent of the nucleus.
Another unusual structure of Trypanosoma brucei is the glycosome. These are tiny bodies in which a respiratory process called glycolysis takes place. Glycolysis is the breakdown of glucose with the production of energy that the organism can use for its life processes.
Along the length of its body, Trypanosoma brucei has an undulating membrane which the trypanosome uses to move about. The single flagellum is attached to this undulating membrane for most of its length.
Trypanosoma brucei is polymorphic. This means that as it goes through its life cycle, its shape changes somewhat. When the pathogen first enters the bloodstream of a human or animal body, it has a long and slender form. But toward the end of its sojourn in a human or animal body, it becomes short and fat. When it then enters the tsetse fly, it again undergoes development. It develops in the gut, and winds up in the saliva, where it can easily be transferred to a human being or animal.
Most of the time, Trypanosoma brucei is called a trypomastigote. This means that the basal body at the foot of its flagellum is behind the nucleus. But in the tsetse fly, it develops into an epimastigote, in which the basal body is in front of the nucleus.
Chagas disease is caused by another species called Trypanosoma cruzi. Patients exhibit various symptoms, such as diarrhea and vomiting. In severe cases, heart damage results.
Chagas disease occurs in Central and South America. The reduviid bug is responsible for spreading this disease. However, unlike the tsetse fly, it does not transmit the disease by its bite, but by its feces. If reduviid fecal material somehow gets into contact with the mucus membranes of the nose or eyes, infection will occur. Or someone may rub the fecal material into the insect bite and so get infected.
Trypanosoma equiperdum is the pathogen that causes dourine, a venereal disease of horses.
Other species of Trypanosoma cause nagana, an animal disease in Africa. Like the sleeping sickness, it is transmitted by the bite of the tsetse fly.
De Duve Institute: Trypanosoma brucei
The Free Dictionary by Farlex: Sleeping Sickness
“Animal Parasites: Their Life Cycle and Ecology” by Oliver Olsen
“RNA Processing: a Practical Approach” by Higgens and Hames
DHPE: Chagas Disease