Sleeping sickness Flashcards
What is sleeping sickness?
human African trypanosomiasis
What are the two forms of sleeping sickness?
- Trypanosoma brucei gambiense - chronic infection lasting years (West Africa)
- Trypanosoma brucei rhodesiense - acute illness lasting several weeks (East and South Africa)
what transmits sleeping sickness?
Tsetse fly
How many people suffer from African trypanosomiasis
66M exposed
300,000 new cases/year
What does the African trypanosomiasis parasite look like?
thin, flagellated parasites
bigger than RBCs
What are the main forms of trypanosomes
Slender and stumpy forms
the stumpy forms survive in tstse and undergo a series of differentiation multiplication events in the fly, ending in the salivary gland. Metacyclic
What happens to the trypanosome once inside a human?
- they change to long slender form
- mulitply by binary fission
What is a characteristic of chronic African trypanosomiasis infection?
regular fluctuations in the numbers of parasites present in the blood
What is the reason for the fluctuations in chronic African trypanosomiasis infection?
- The surface molecule variable surface glycoprotein (VSG)
- a thick surface coat, each different enough to be encoded by a different gene
What happens when the immune system recognises a VSG?
- it makes antibodies (few days)
- kills 99.9%
- those not killed divide and grow
- repeat
how do trypanosomes change their VSG?
- A single VSG gene out of the total repetoire is expressed when it is duplicated and translocated to an expression site near a telomere
- the switch from one to another is effected by the degradation of one such copy and replacement by a copy of another gene
How does the trypanosomes express express one VSG at a time
An extra copy of some VSG genes that are expressed are also present in the genome
known as an EXPRESSION LINKED COPY
what is the site of VSG expression
telomeres. they have highly repetitive stretches of DNA such as short tandem repeats, so more variation can be generated
What is an expression site body
It is a special place within the trypanosome nucleus where all the VSG information is handled. And all the necessary molecules required for expression are sequestered there.
What is quorum sensing
A way of trypanosome parasites to sense the number of healthy slender forms present, and the inflammatory status of the host. They can then shift to the stumpy form so this can be transmitted to new tstse fly.
