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Human Parasites: Survival strategy of the Trypanosoma brucei

written by: Sonal Panse•edited by: Paul Arnold•updated: 3/31/2011

The human parasite Trypanosoma brucei has a unique survival strategy. Every time the host immune system detects it, it changes its appearance.

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    Trypanosoma brucei

    Trypanosoma brucei is a parasite that causes the disease known as sleeping sickness. This disease mostly occurs on the African continent and is spread by the Tsetse fly. It can infect humans and other mammals.

    The Trypanosoma brucei enters the bloodstream of the infected person or animal and starts to replicate. It remains in the bloodstream; it does not enter the cells. It moves around in the bloodstream, infects the brain and attacks the central nervous system.

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    The Survival Strategy of the Trypanosoma brucei

    The most dreadful part is that once the parasite Trypanosoma brucei invades a body it can be a particularly tough customer to get rid of. It routinely defeats the attempts of the body's immune system to get rid of it. This long baffled the medical community; one would think, given the Trypanosoma brucei's penchant for extracellular activities, that the immune system would be able to detect and decimate it. But, no, the parasite still reappears like a bad penny. What gives? Well, scientists have now discovered how the survival strategy of the Trypanosoma brucei works.

    The Trypanosoma brucei, it seems, is the escape artist of the parasite world. It is capable of rearranging its DNA and changing its exterior surface, and thereby changing its whole appearance. It pulls this trick just as the immune system has detected it and is starting to destroy the infection. With the DNA and surface coat changed, the immune system fails to detect the Trypanosoma brucei and this helps it to escape destruction.

    The surviving Trypanosoma brucei now initiates a new infection. The body's immune system once more swings into action. Then, guess what? - the Trypanosoma brucei changes itself yet again. This goes on and on and finally the infected person is too weakened to continue resisting and may die.

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    Variant Surface Glycoprotein (VSG)

    What makes the bacteria so insidious? The surface of the Trypanosoma brucei is made of one variant surface glycoprotein (VSG). Each Trypanosoma brucei has around a thousand VSG genes. It can also create many new variations of VSG genes.

    Each single VSG gene transcription occurs in an expression site located in the telomeres or ends of specific chromosomes. Each trypanosome parasite has 20 bloodstream forms of VSG expression sites (BESs). Only one BES can be active at a time, expressing only one VSG. A new one is activated only after the first one is silenced.

    VSG switching is carried out during an infection to outwit the host immune system. The Trypanosoma brucei can activate different VSG genes for different hosts.