Chapter 7 malaria study guide

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20 Mar 2011

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Chapter 7: Malaria, Another Fever Plague
A Look Back
Records of malaria have been found in the Ebers papyrus, clay tablets
from the library of king Ashurbanipal and in Chinese medical text.
Records describe, enlarged spleens, periodic fevers, headache, chills
and fever.
Malaria came to Europe from Africa via the Nile valley or by close
contact between Europeans and the Asia Minor.
Hippocrates describes two types of malaria, the benign tertian with
recurrent fevers every third day and the quartan with fevers on the
fourth day. He also noted that people living near marshes had
enlarged spleens.
Hippocrates did not describe the malignant tertian malaria in Greece,
even though it was present in the Roman republic by 200 BC.
Spread across Europe reaching Spain and Russia by the 12th century
and England in the 14th century. By the 1800s it was found worldwide.
On 20 October 1880, Laveran examined blood from a soldier with
malaria and found transparent globules containing black-brown
malaria pigment within the red blood cells. He also found mobile
filaments emerging from the clear spherical bodies, a process he called
Laveran also discovered that some patients had blood cells shaped like
crescents. It wasnt until 1884 that Laverns work was confirmed.
Rosss mentor Manson encouraged him to study mosquito
He went on studying various mosquitoes but it wasnt until 1897 that
he studied the anopheles mosquito, which can carry the malaria
In 1898 Ross was able to determine that malaria was not conveyed by
dust or bad air but that it had infectious stages in the mosquito to the
salivary glands
Grassi recognized that he had to identify the mosquito that
transmitted human malaria and then demonstrated the mosquito cycle
for human malaria.
Grassi demonstrated that the mosquito that bites a malaria suffer,
could give malaria to a healthy individual.
Malaria is induced in a host by the introduction of sporozoits through
an infectious female mosquito, but the parasites do not immediately
appear in the blood.
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The infected female anopheline mosquito injects sporozoits that go to
the liver
The Disease Malaria
There are four plasmodiums that are specific for humans: P.
falciparum, P. vivax, P. ovale, and p. malariae. They are transmitted
through the bite of an infected anopheline mosquito, which injects
sporozoits from her salivary glands when feeding.
The number of sporozoits inoculated is usually less than 25.
The sporozoits travel via the bloodstream to the liver cells.
The entire process takes less than 1 hour.
The parasite multiples asexually to produce 10000 or more infective
They then invade erythrocytes.
They reproduce asexually producing merozoites, which are the
pathogenesis of the disease.
Merozoites released from the erythrocytes invade other red cells and
continue the cycle of 10-fold parasite multiplication with extensive red
blood cell destruction.
Some of the merozoits do not divide; instead they differentiate into
male or female gametocytes.
When injected by a female mosquito, the male gametocyte divides into
eight-flagellated microgametes which escape from the red cells this
process is called exflagellation. They swim to the macrogamete and
one fertilizes it.
The motile zygote, called the ookinete moves either between or through
the cells of the stomach wall
The encysted zygote on the outside of the mosquitos stomach is an
oocyst and multiplies and produces threadlike sporozoits
The oocyst bursts releasing its sporozoits into the body cavity.
The sporozoits find their way to the salivary glands.
When the female feeds again, the transmission cycle has been
In P. vivax, P. ovale and P. falciparum the period between fever bursts
is 48 hours, and for P. malariae it is 72 hours.
The fever may reach up to 41 degrees and corresponds to the rupture of
the red cell as merozoites are released from the infected red cell.
During the first few weeks of infection the spleen is palpable because it
is swollen from the accumulation of the parasitized red cells and the
proliferation of white cells.
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