Malaria is caused by a parasite that is transmitted from
one human to another by the bite of infected Anopheles
mosquitoes. In humans, the parasites (called sporozoites)
migrate to the liver where they mature and release
another form, the merozoites. These enter the bloodstream
and infect the red blood cells.
The parasites multiply
inside the red blood cells, which then rupture within 48
to 72 hours, infecting more red blood cells. The first
symptoms usually occur 10 days to 4 weeks after
infection, though they can appear as early as 8 days or
as long as a year later. Then the symptoms occur in cycles of 48
to 72 hours.
The majority of symptoms are caused by
the massive release of merozoites into the bloodstream, the anaemia
resulting from the destruction of the red blood cells, and the problems
caused by large amounts of free haemoglobin released into the
circulation after red blood cells rupture.
Malaria can also be
transmitted congenitally (from a mother to her unborn
baby) and by blood transfusions. Malaria can be carried by
mosquitoes in temperate climates, but the parasite disappears over the
winter.
The disease is a major health problem in
much of the tropics and subtropics.
The CDC estimates
that there are 300 to 500 million cases of malaria each
year, and more than one million people die. It presents the
greatest disease hazard for travellers to warm climates.
In some areas of
the world, mosquitoes that carry malaria have developed
resistance to insecticides, while the parasites have
developed resistance to antibiotics. This has led to difficulty in
controlling both the rate of infection and spread of this disease.
Falciparum malaria,
one of four different types, affects a greater proportion
of the red blood cells than the other types and is much
more serious. It can be fatal within a few hours of the
first symptoms.
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