Sleeping sickness (African trypanosomiasis) in humans is caused by infection with which one of the following protozoan parasites?

Introduction:
Sleeping sickness, more correctly called African trypanosomiasis, is a serious tropical disease affecting humans and other animals in parts of Africa. It is transmitted by the bite of infected tsetse flies and can cause severe neurological symptoms and even death if untreated. This question asks you to identify the protozoan parasite responsible for causing this disease from among several well known protozoa that cause human infections.

Given Data / Assumptions:
- The disease mentioned is sleeping sickness in humans. - The options are Plasmodium, Entamoeba, Giardia and Trypanosoma. - We assume knowledge of common protozoan diseases such as malaria, amoebiasis and giardiasis. - The question focuses on matching the correct pathogen to sleeping sickness.

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 by tsetse flies and invade the blood and central nervous system, leading to fever, lymph node enlargement and later disturbances of sleep and consciousness. Plasmodium species cause malaria, Entamoeba histolytica causes amoebic dysentery and Giardia lamblia causes giardiasis, a diarrhoeal disease. Therefore, among the options given, Trypanosoma is the correct parasite responsible for sleeping sickness.

Step-by-Step Solution:
Step 1: Associate the term sleeping sickness with African trypanosomiasis, a vector borne protozoan disease. Step 2: Recall that trypanosomes are elongated flagellated protozoa transmitted by tsetse flies. Step 3: Recognise that Plasmodium species are transmitted by female Anopheles mosquitoes and cause malaria, not sleeping sickness. Step 4: Remember that Entamoeba histolytica is an amoeba causing amoebic dysentery and liver abscess, transmitted through contaminated food and water. Step 5: Note that Giardia lamblia is a flagellated protozoan that infects the small intestine and causes diarrhoea, known as giardiasis. Step 6: Conclude that Trypanosoma is the only option correctly associated with sleeping sickness.

Verification / Alternative check:
Parasitology and tropical medicine textbooks clearly state that African sleeping sickness is caused by Trypanosoma brucei subspecies. They detail the life cycle involving tsetse flies as vectors and note the progression of disease from haemolymphatic stage to neurological involvement. Malaria sections list Plasmodium species such as P. vivax and P. falciparum, while amoebiasis and giardiasis chapters attribute these diseases to Entamoeba and Giardia respectively. These independent sources confirm that Trypanosoma is the correct answer for sleeping sickness.

Why Other Options Are Wrong:
Plasmodium: Causes malaria, characterised by periodic fever, chills and anaemia, not primarily by sleep disturbances associated with trypanosomiasis. Entamoeba: Refers mainly to Entamoeba histolytica, responsible for amoebic dysentery and liver abscess, not sleeping sickness. Giardia: Specifically Giardia lamblia (also called G. intestinalis), which causes intestinal infection and diarrhoea, not a vector borne neurological disease.

Common Pitfalls:
Students may sometimes pick Plasmodium because it is the most famous protozoan parasite, or they may confuse the names of diseases and parasites due to similar sounding Latin terms. Another issue is mixing up sleeping sickness with other tropical diseases like malaria or dengue. A helpful memory device is to link trypanosomiasis, tsetse fly and Trypanosoma together, reinforcing that these three Ts go with sleeping sickness.

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