Transmission of this parasite occurs most often from the bite of a tsetse fly in endemic areas. Due to the natural restriction of the tsetse fly to Africa, the term Afican sleeping sickness is a suitable name for this disease. First, it describes where T. brucei can be contracted. Secondly, sleeping sickness is an excellent descriptor of the symptoms of disease progression. Without treatment people will begin to experience extreme lethargy and experience a variety of symptoms including changes in personality. Eventually, they will succumb to the disease and slip into a coma.
For African sleeping sickness there are two major forms of disease progression based on where the parasites are located. The initial phase is found in the blood and peripheral tissue spaces where the parasites will readily grow and divide. The patient’s immune system will keep up with the parasites as best it can. The attack of the immune system triggers a phenomenon in the parasite known as antigenic variation in which the parasites will adapt to the immune system as a population. This causes a wave of parasite numbers that will increase and decrease as the parasites and the immune system adapt to each other. At some point during all of this, parasites will cross the blood-brain barrier. At this point the disease has turned for the worse and the patient may have reached a point of no return.
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