Sleeping sickness in humans (African trypanosomiasis) is caused by infection with which protozoan organism?

Introduction:
Sleeping sickness, or African trypanosomiasis, is a serious disease found in certain parts of Africa. It affects humans and other animals and can lead to severe neurological symptoms and death if untreated. Understanding which parasite causes this disease is important in basic parasitology and general knowledge. This question asks you to identify the correct protozoan genus responsible for sleeping sickness from among several well known parasites that cause other human diseases.

Given Data / Assumptions:
- The disease mentioned is sleeping sickness in humans. - Options include Plasmodium, Entamoeba, Giardia and Trypanosoma. - We assume standard definitions of common protozoan diseases. - The question focuses on the causal organism rather than the vector.

Concept / Approach:
Sleeping sickness is caused by protozoan parasites of the genus Trypanosoma, mainly Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense. These parasites are transmitted to humans through the bite of infected tsetse flies. Once in the bloodstream, they can invade the central nervous system, causing disturbances of sleep and consciousness. Plasmodium species cause malaria, Entamoeba histolytica causes amoebic dysentery and liver abscess, and Giardia lamblia causes giardiasis (intestinal infection). Therefore, only Trypanosoma corresponds to sleeping sickness.

Step-by-Step Solution:
Step 1: Associate the term sleeping sickness or African trypanosomiasis with Africa and tsetse flies as vectors. Step 2: Recall that the protozoan genus linked with tsetse flies and sleeping sickness is Trypanosoma. Step 3: Recognise that Plasmodium species are transmitted by Anopheles mosquitoes and cause malaria, characterised by fever and chills. Step 4: Remember that Entamoeba histolytica is an amoeba causing amoebic dysentery and liver abscess through contaminated food and water. Step 5: Note that Giardia lamblia infects the small intestine and causes diarrhoea, often linked with contaminated water, but not sleeping sickness. Step 6: Conclude that Trypanosoma is the only option that correctly matches sleeping sickness in humans.

Verification / Alternative check:
Parasitology references clearly list African sleeping sickness under trypanosomiasis and give the scientific names Trypanosoma brucei gambiense and T. brucei rhodesiense. They describe the life cycle involving tsetse flies and the progression of symptoms from fever to central nervous system involvement and disturbed sleep. Malaria chapters attribute that disease to Plasmodium species, amoebiasis chapters to Entamoeba histolytica and giardiasis chapters to Giardia lamblia. This consistent information across sources confirms that Trypanosoma is responsible for sleeping sickness.

Why Other Options Are Wrong:
Plasmodium: Causes malaria, which presents with periodic fever, chills and anaemia, not the distinctive sleep disturbances of sleeping sickness. Entamoeba: Specifically Entamoeba histolytica causes amoebic dysentery and liver abscess, mainly affecting the intestine and liver. Giardia: Giardia lamblia causes intestinal infection and diarrhoea, often leading to malabsorption, but not a neurological sleep related disease.

Common Pitfalls:
Students may be tempted to choose Plasmodium because malaria is the most widely known protozoan disease. Others may mix up the names of parasites because they all sound similar. A useful memory aid is to link the letter T in Trypanosoma, tsetse fly and trypanosomiasis with sleeping sickness, reinforcing that they belong together. Plasmodium, on the other hand, should be firmly linked with malaria.

Final Answer:
Sleeping sickness in humans is caused by infection with the protozoan parasite Trypanosoma.