Action of PF on humans
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Back to Malaria as an Infectious DiseaseAction of PF on humansThe first event in catching malaria is to be bitten by a mosquito that is carrying PF (above left). Some PF cells are injected into the bloodstream by the mosquito and these PF cells burrow into a cell in the person's liver (above right). Inside this cell the PF grows until there are many hundreds of cells (below left) and then the liver cell bursts releasing the PF cells into the bloodstream (below right).
( http://www.tigr.org/tdb/edb/pfdb/images.html These cells are different to the ones injected by the mosquito and they enter red blood cells where they will grow until there are about 20 cells (below left). The red blood cell bursts and the PF cells each enter a new red blood cell (below right). The infection of red blood cells occurs in regular waves and the periodic fevers are caused by the contents of the burst red blood cells.
(http://www.tigr.org/tdb/edb/pfdb/images.html The diagnosis for malaria still depends on seeing PF in red blood cells (as in the photos above). If the PF is picked up by a feeding mosquito then the mosquito can become infected and transmit the PF to another person. PF protects itself from a person's antibodies by hiding inside cells. Why do some diseases persist and others disappear?The reasons are rarely simply but we can look at any disease and try and understand by using the idea of 'transmission index' (R)
So, if R > 1 then the number of people with the infectious disease will increase and if R < 1 the number will decrease and will eventually die out: What happened in Britain in the 1880's?
What do you think happened to the transmission index of malaria in Britain in the 1880s? What factors do you think might have caused this?
R < 1. No one knows what caused the decrease in transmission index but some people believe that the appearance of very cheap sheet glass for windows that occurred in the 1880s resulted in less mosquito bites! In sub-Saharan Africa PF is endemic and transmission is stable - R > 1 Without human intervention, is the transmission index always the same for any one disease? With human intervention, how could hte transmission index of malaria be reduced in Africa? |