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| [Plasmodium
falciparum] [Plasmodium malariae] [Plasmodium ovale] [Plasmodium vivax] |
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Causal Agents:
Blood parasites of the genus Plasmodium. There are approximately 156 named species of Plasmodium which infect
various species of vertebrates. Four are known to infect humans: P. falciparum,
P. vivax, P. ovale, and P. malariae.
The malaria parasite life cycle involves two hosts.
During a blood meal, a malaria-infected female Anopheles mosquito inoculates sporozoites into the human host
.
Sporozoites infect liver cells
and mature into schizonts
, which rupture and release merozoites
.
(Of note, in P. vivax and P. ovale a dormant stage
[hypnozoites] can persist in the liver and cause relapses by invading the bloodstream weeks, or even years later.)
After this initial replication in the liver (exo-erythrocytic schizogony
), the parasites undergo asexual multiplication in the erythrocytes (erythrocytic schizogony
).
Merozoites infect red blood cells
.
The ring stage trophozoites mature into schizonts, which rupture releasing merozoites
.
Some parasites differentiate into sexual erythrocytic stages (gametocytes)
.
Blood stage parasites are responsible for the clinical manifestations of the disease.
The gametocytes, male (microgametocytes) and female (macrogametocytes), are ingested by an
Anopheles mosquito during a blood meal
.
The parasites’ multiplication in the mosquito is known as the sporogonic cycle
.
While in the mosquito's stomach, the microgametes penetrate the macrogametes generating zygotes
.
The zygotes in turn become motile and elongated
(ookinetes)
which invade the midgut wall of the mosquito where they develop into oocysts
.
The oocysts grow, rupture, and release sporozoites
, which make their way to the mosquito's salivary glands.
Inoculation of the sporozoites into a new human host perpetuates the malaria life cycle
.
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