The Rhodesiense Life Cycle
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Trypanosoma brucei rhodesiense ("T.b.r") is a parasite called a trypanosome, that causes the East African variation of trypanosomiasis, better known as African sleeping sickness. The more prevalent type of trypanosomiasis is West African sleeping sickness caused by Trypanosoma brucei gambiense ("T.b.g."). This article focuses on T.b.r. and East African sleeping sickness, the more acute form of the disease. T.b.r sleeping sickness accounts for about 10 percent of all cases and occurs primarily in East and Southeast Africa. Severe sleep disturbances are one symptom of the disease, hence the term "sleeping sickness". If left untreated, the disease is fatal. Drug protocol is the only treatment method.
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The T.b.r. trypanosome lives in Africa, primarily in the vegetation next to large bodies of water or regions of scrub desert. The life cycle begins when an infected tse-tse fly bites an uninfected human being or animal. Only newly-hatched flies can carry the disease. As the young fly bites into the skin, the fly injects trypanosomes, specifically metacyclic trypomastigotes, into the skin tissue.
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The trypomastigotes travel through the bloodstream, developing into bloodstream trypomastigotes. As they travel, the trypomastigotes reproduce through binary fission, meaning each cells replicates its DNA nucleus inside its cell walls and then splits into two separate cells, each now with its own DNA nucleus.
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The host is now in the first stage of trypanosomiasis, the hemolymphatic stage. The increasing number of bloodstream trypomastigotes infects the skin tissue and blood fluids, such as lymph and spinal fluid. As the immune system fights off this invasion, the host will experience fever, weakness, joint pains, headaches and itching. Animals will suffer from appetite and weight loss.
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The host's immune system will kill many of the trypomastigotes. But through the process of antigenic variation, where each reproduction of the trypomastigotes allows for minor variations in the new parasitic cells that the host's immune system cannot identify and destroy and some trypomastigotes survive to cause the next stage of infection.
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In the second more serious stage of the disease, the trypomastigotes infect the host's central nervous system. Now the organs become distressed, causing cardiovascular, endocrine and kidney disorders, anemia, spontaneous abortions, infected fetuses and edema. Behavioral disorders also appear, such as confusion, torpor, poor coordination, mood swings and the sleep disturbances for which the disease is named. The disease is fatal if not treated at this stage.
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At this stage, the trypomastigotes are fully infective, meaning they can cause infection. An uninfected tse-tse fly bites the host and ingests the trypomastigotes.
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Inside the fly, the trypomastigotes travel through the bloodstream and settle in the intestines. Here they again reproduce using binary fission and the parasite becomes ready to infect another host. This process takes about 3 weeks.
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The infected tse-tse fly bites an uninfected human being and the cycle begins again. Infected flies remain infected for life, which means they can infect many people before they die.
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