Plasmodium vivax, mosaic of forms; 900x.
Plasmodium vivax, sporozoite
in culture; 900x.
Apicomplexans
We continue with apicomplexans, but now we focus on Plasmodium and allies.
Eucoccidiorida: Plasmodium
Now we examine the protozoan responsible for malaria: Plasmodium.
This bug shows all of the stages noted for coccidian parasites (merogony, gametogony,
sporogony). It has also been extensively studied, due to its global distribution
and pathogenicity in tropical systems. The life cycle begins with sporozoites
injected into the blood by mosquitos.
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They then enter the liver for the first-generation schizogony. Merozoites are then released into the blood to infect red blood cells (erythrocytes). Then the merozoites begin a cycle of reinfection: merozoites become trophozoites, which then undergo schizogony to become more merozoites.
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 Plasmodium vivax, trophozoite in blood; 900x. |
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Some trophozoites become gametocytes by gametogony. These gametocytes then await consumption by a mosquito to undergo sporogony and complete the cycle.
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 Plasmodium vivax, gametocyte in blood; 900x. |
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Plasmodium falciparum:
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 Plasmodium falciparum, gametocyte in blood; 900x. |
Plasmodium malariae:
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 Plasmodium malariae, gametocyte in blood; 900x. |
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 Plasmodium malariae, schizonts in blood; 900x. The big cell is a white blood cell. |
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 Plasmodium malariae, trophozoite in blood; 900x. |
Cell components: To distinguish Plasmodium stages from normal blood components, here are a couple of white blood cells.
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 White blood cells in blood: neutrophil; 450x. |
Piroplasmasina: Babesia bigemina
This piroplasm is recognized by its pyriform shape in the erythrocyte. Transmitted
by the tick Boophilus annulatus, it was responsible for Texas red-water
fever. A related piroplasm may be responsible for Nantucket Island fever.
Babesia bigemina in blood: eosinophil; 900x.
Ciliophorate parasites
There aren't that many parasitic ciliates when compared to other protozoa,
though there are many commensals and beneficial symbionts. One, Balantidium
coli, has similar pathologies to Entamoeba histolytica. Balantadium
is thought to have originally derived from pig symbionts.
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 Balantidium coli in fecal smear; 450x. The cilia can be seen more clearly here. |
Some commensals become opportunistic pathogens, including Pneumocystis carinii. This critter takes advantage of those with an impaired immune system. Note that we're not quite sure if Pneumocystis is a fungus or a ciliate.
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 Pneumocystis carinii cysts in lung tissue; 900x. |
