What happens in sleeping sickness, exactly?

What is it?

Sleeping sickness, also known as African trypanosomiasis, is a parasitic disease caused by protozoa of a species called Trypanosoma brucei.

The first symptoms appear 1-3 weeks after infection. These include fever, headache, itchiness, and joint pain. Weeks to months later the second phase of the disease sets in, and now patients experience things like confusion, poor coordination, numbness, and trouble sleeping. The disease gets its name from these distinct sleeping difficulties – patients often fall asleep during the day, and can’t sleep normally during the night. Without treatment, the disease leads to irreversible neurological damage, then coma, and finally death.

95% of sleeping sickness cases occur in Tanzania, Uganda, Malawi, and Zambia. In 2010, the disease caused 9000 deaths. About 30 000 people are thought to be currently infected, with  7000 new cases per year.

What causes it?

Protozoa are little organisms composed of just one cell. Unlike viruses and bacteria, they have a nucleus, and they resemble animal cells quite a lot.

Humans and other animals acquire sleeping sickness, when they are infected with the protozoan Trypanosoma brucei. This species is transmitted through the bite of a tsetse fly, which acts both as a host and a transmitter of the species. The fly sucks blood from mammals, and while doing so, the parasite gains access to the animal´s tissues.

What happens during it?

When the protozoa enter the body, they first start to divide in the bloodstream and the lymphatic system. The body’s immune system uses the surface proteins of pathogens to identify them and to eventually destroy them, but in Trypanosoma brucei, these proteins mutate to other forms so fast, that the immune system isn’t able to keep up – whenever the body thinks it knows how to kill the invaders, its measures prove useless as the surface proteins are already different. The non-specific first-stage symptoms including fever and headache occur mostly because the body realizes that there’s something wrong. It starts an immune reaction, including things like inflammation, with the aim of killing the pathogens.

The brain and spinal cord are protected from infection with the blood-brain-barrier, but if  sleeping sickness isn’t treated, the protozoa will eventually pass it. In the central nervous system the parasites can cause a number of symptoms as they do their damage and as the immune reaction also damages the brain. The characteristic sleeping problems arise, when the protozoa produce a compound called tryptophol, which induces sleep in humans. It is thought to function in approximately the same way as sleep-related neurotransmitters and hormones normally do in the brain.

How can it be treated?

If the disease is noticed during the first stage, certain antiparasitic drugs can be injected to the bloodstream of the patient in the hope that it kills the protozoa. If the disease has progressed to the second stage and hence invaded the central nervous system, other intravenous drugs should be used. There are two subtypes of sleeping sickness, and for the other one there only exists one treatment option for the second stage, and this medication kills 5% of its users.


Sources: https://en.wikipedia.org/wiki/African_trypanosomiasis, http://emedicine.medscape.com/article/228613-overview#a5, https://en.wikipedia.org/wiki/Protozoa, https://en.wikipedia.org/wiki/Tryptophol, http://www.cdc.gov/parasites/sleepingsickness/biology.html, http://www.cdc.gov/parasites/sleepingsickness/treatment.html, http://dna.kdna.ucla.edu/parasite_course-old/african%20tryps%20new_files/subchapters/Pathogenesis.htm, http://www.merckmanuals.com/professional/infectious-diseases/extraintestinal-protozoa/african-trypanosomiasis, http://www.wikidoc.org/index.php/African_trypanosomiasis_pathophysiology


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