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Life Cycle of the Malaria
Parasite
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A female Anopheles
mosquito carrying malaria-causing parasites feeds on
a human and injects the parasites in the form of
sporozoites into the bloodstream. The sporozoites
travel to the liver and invade liver cells.
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Over 5-16 days*, the
sporozoites grow, divide, and produce tens of
thousands of haploid forms, called merozoites, per
liver cell. Some malaria parasite species remain
dormant for extended periods in the liver, causing
relapses weeks or months later.
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The merozoites exit the
liver cells and re-enter the bloodstream, beginning
a cycle of invasion of red blood cells, asexual
replication, and release of newly formed merozoites
from the red blood cells repeatedly over 1-3 days*.
This multiplication can result in thousands of
parasite-infected cells in the host bloodstream,
leading to illness and complications of malaria that
can last for months if not treated.
-
Some of the
merozoite-infected blood cells leave the cycle of
asexual multiplication. Instead of replicating, the
merozoites in these cells develop into sexual forms
of the parasite, called male and female gametocytes,
that circulate in the bloodstream.
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When a mosquito bites an
infected human, it ingests the gametocytes. In the
mosquito gut, the infected human blood cells burst,
releasing the gametocytes, which develop further
into mature sex cells called gametes. Male and
female gametes fuse to form diploid zygotes, which
develop into actively moving ookinetes that burrow
into the mosquito midgut wall and form oocysts.
-
Growth and division of
each oocyst produces thousands of active haploid
forms called sporozoites. After 8-15 days*, the
oocyst bursts, releasing sporozoites into the body
cavity of the mosquito, from which they travel to
and invade the mosquito salivary glands. The cycle
of human infection re-starts when the mosquito takes
a blood meal, injecting the sporozoites from its
salivary glands into the human bloodstream .
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