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252 DISTRICT LABORATORY PRACTICE I N TROPICAL COUNTRIES

5.7

Plasmodium falciparum

Widespread in tropics. Often high parasitaemia. Only trophozoites and

gametocytes usually seen.

Trophozoites Small rings, occasionally larger

rings in heavy infections.* Often with double chromatin dot. May lie on red cell membrane

(accol forms).

* Parasites are difficult to recognize ifpatient has taken antimalarials.Trophozoites of resistant strains can appearthick and distorted.

Schizonts Only seen occasionally in severe

infections. Usually with 2 or 4 merozoites

and pigment.

Gametocytes Banana shaped. Rounded forms may be seen if

film dries slowly.

Host cell Often contains several parasites. Irregular mauve-red Maurers

dots (clefts) seen in cells withmature rings.

Plasmodium malariae Low prevalence in tropics and

subtropics. Rarely more than 1% of cells

infected (easily missed). Trophozoites, schizonts and

gametocytes usually seen.

Trophozoites Thick, neat, densely stained. Yellow-brown pigment in late

trophozoites. Band forms can be seen in thin

films. Occasionally birds-eye ring

form may be seen.

Schizonts Small with neatly arranged (up to

12) merozoites. Yellow-brown pigment.

Gametocytes Small, round or oval (can be

difficult to differentiatefrom late trophozoites).

Yellow-brown pigment.

Host cell No changes. Older cells parasitized.

Plate 5.43 P.falciparum. a Trophozoites and gametocytes in thin film.b Young schizont (rare), and trophozoites. c Many trophozoites, gametocyte,and white cells containing pigment in Fields stained thick film. d Thick filmfrom patient with sickle cell disease and falciparum malaria. Note, blue stipplingin background (reticulocytosis) and nucleated red cell nucleus (above trophozoite).

Plate 5.46 P.malariae. a Trophozoites (Birds eye and band forms, gametocyte,and schizont in thin film. b Schizont, trophozoite, and gametocyte in thin film.c Trophozoites, schizonts, and gametocyte in Fields stained thick film.

a b

c d

a b

c

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PARASITOLOGICAL TESTS 253

5.7

Plasmodium vivax Widespread in tropics and

temperate areas. Rarely more than 2% of cells

infected. Trophozoites, schizonts and

gametocytes, usually seen.

Trophozoites Large and amoeboid. Cytoplasm fragmented in thick

films. Fine pigment.

Schizonts Large, round or irregular in form. Contain up to 24 or more

merozoites and fine pigment.

Gametocytes Large, round or irregular in form

(small forms also). Scattered pigment.

Host cell

Enlarged, irregular in shape, palestaining.

Schuffners dots present (pH7.1). Seen indistinctly aroundparasites in thick films.

Several parasites in a cell withsome strains.

Plasmodium ovale Low prevalence, mainly in West

Africa (also elsewhere). Rarely more than 2% of cells

infected (young cellspreferentially parasitized).

Trophozoites, schizonts andgametocytes usually seen.

Trophozoites Small and compact (can resemble

P. malariae in thick films). Small amount of pigment.

Schizonts Small and compact. Contain up to 12 merozoites.

Gametocytes Small and round.

Difficult to differentiate from latetrophozoites.

Host cell About 2030% of cells may

become oval with fimbriated(ragged) ends.

Schuffners dots are prominent(pH 7.1). Seen indistinctlyaround parasites in thick film.

Plate 5.44 P.vivax. a Trophozoites, gametocytes, and schizonts in thin film.b Schizont (mature), gametocyte, and trophozoite in thin film. c Trophozoitesin Fields stained thick film.

Plate 5.45 P.ovale. a Trophozoite, schizont, and gametocyte in thin film.b Trophozoite, schizont, and gametocyte in thin film. c Trophozoite,gametocyte, and schizont in Fields stained thick film.

a b

c

a b

c