Comparative account of four species of human infecting malarial parasite:
1. P. Vivax:
i. Geographical distribution:
In tropical, subtropical and warmer temperate regions.
ii. Duration of pre-erythrocytic schizogony:
10-14 days
iii. No. of crypto- zoites formed per schizont:
10,000-12,000 (approx.)
iv. Incubation period:
14 days
v. Duration of erythrocytic schizogony:
2 days
vi. Form in peripheral blood during erythrocytic schizogony:
Trophozoites, schizonts, and game- tocytes.
Trophozoites:
a. Ring form:
Size, 2.5 µm. Cytoplasm opposite the nucleus is thicker.
b. Growing form:
Irregular shape with a vacuole and actively amoeboid in nature.
Schizont:
Size, 9-12 f/m. Regular, almost completely fills an enlarged RBC.
Merozoite:
12-24; arranged in the form of a ‘rosette’ (usually in 2 rows).
Malarial pigments (haemozoin):
Yellowish brown; fine granules and rodlets.
Infected host RBC:
Enlarged, red Schuffner’s dots present.
Gametocytes RBC:
Spherical or globular. Much larger than a RBC. Pigment granules evenly distributed. Host cell enlarged with Schuffner’s dots.
Duration of sexual cycle:
10-14 days.
Type and effects of malarial fever:
Benign tertian. Death rate low.
2. P. Falciparum:
i. Geographical distribution:
In tropical, subtropical and warmer temperate regions.
ii. Duration of pre-erythrocytic schizogony:
5-6 days
iii. No. of crypto- zoites formed per schizont:
40,000 (approx.)
iv. Incubation period:
12 days
v. Duration of erythrocytic schizogony:
1 ½ -2 days
vi. Form in peripheral blood during erythrocytic schizogony:
Ring and crescents only. Growing trophozoites and schizonts rarely.
Trophozoites:
a. Ring form:
Size, 1.25-1.5 µm. Cytoplasm fine and regular in outline, often with two nuclei.
b. Growing form:
Compact form consisting of dark brown or black pigment granules and collect into a single mass at an early stage.
Schizont:
Size 4.5-5 µm. Fills 20/3 of a RBC.
Merozoite:
8-18, arranged in a grape-like cluster.
Malarial pigments (haemozoin):
Dark brown or blackish. Coarse granules in a compact mass.
Infected host RBC:
Not enlarged, creation, reddish violet colour and Maurer’s dots seen.
Gametocytes RBC:
Saucer or crescentic in outline. Larger than a RBC. Host cell hardly recognisable. Pigment granules around nucleus.
Duration of sexual cycle:
10-12 days.
Type and effects of malarial fever:
Malignant tertian. Death rate high.
3. P. Malariae:
i. Geographical distribution:
In tropical and subtropical regions.
ii. Duration of pre-erythrocytic schizogony:
7-12 days
iii. No. of crypto- zoites formed per schizont:
2,000 (approx.)
iv. Incubation period:
18-24 days
v. Duration of erythrocytic schizogony:
3 days
vi. Form in peripheral blood during erythrocytic schizogony:
Trophozoites, schizonts and gametocytes.
Trophozoites:
a. Ring form:
Same as P. vivax.
b. Growing form:
Assumes a band like appearance but slightly amoeboid. Vacuole disappears at an early stage.
Schizont:
Size 6.5-7 µm. Regular, almost fills a normal sized RBC.
Merozoite:
6-12; arranged around a central mass of pigment and giving the appearance of a “daisy head”.
Malarial pigments (haemozoin):
Dark brown to black. Abundant as coarse granules.
Infected host RBC:
Not enlarged, Ziemann’s dots on prolonged staining seen.
Gametocytes RBC:
Round or ovoid. Host cell not enlarged. Pigment granules at center and periphery.
Duration of sexual cycle:
25-28 days.
Type and effects of malarial fever:
Quartan.
Severe.
4. P. Ovale:
i. Geographical distribution:
Tropical Africa.
ii. Duration of pre-erythrocytic schizogony:
9 days
iii. No. of crypto- zoites formed per schizont:
15,000 (approx.)
iv. Incubation period:
14 days
v. Duration of erythrocytic schizogony:
2 days
vi. Form in peripheral blood during erythrocytic schizogony:
Same as P. malariae.
Trophozoites:
a. Ring form:
Same as P. vivax.
b. Growing form:
Same as P. malariae.
The pigment granules are coarse and dark brown in colour.
Schizont:
Size, 6.2 µm. Fills about three quarters of a RBC.
Merozoite:
6-12; irregularly arranged.
Malarial pigments (haemozoin):
Dark yellowish brown; less abundant and coarse granules.
Infected host RBC:
Slightly enlarged, oval shape, fimbriated. Schuffner’s dots seen.
Gametocytes RBC:
Round or ovoid. Host cell slightly enlarged with James dots. Pigment granules evenly distributed.
Duration of sexual cycle:
16 days.
Type and effects of malarial fever:
Ovale/mild tertian Severe.