Malaria 611 



The invaded corpuscle is not enlarged and usually retains its normal 

 shape, color, and staining reaction. 



The cytoplasm of the mature microgametocyte stains a light blue to 

 pale lavender (Wright's stain); that of the macrogametocyte, a fairly 

 deep blue. The nuclear material of the microgametocyte stains a light 

 pink and may occupy half the diameter of the parasite; that of the 

 macrogametocyte is more compact and is usually stained a bright red or 

 purple. The dark brown, or greenish brown, pigment granules are usually 

 scattered through the cytoplasm in the microgametocyte; more or less 

 restricted to the peripheral cytoplasm in the macrogametocyte. Each 

 gametocyte almost fills the unenlarged corpuscle. 



Erythrocytic phase in P. ovale (Fig. 13.5). The small ring stages (108) 

 are usually coarser and stain more deeply than those of P. falciparum. 

 Both young and later growth stages resemble those of P. malariae in their 

 compact form, but are larger and contain slightly lighter, finer, and less 

 abimdant pigment granules. The corpuscle is somewhat enlarged and is 

 sometimes oval, occasionally rounded at one end and tapering at the 

 other, or often irregular or ragged in outline. Schriffner's dots are often 

 distinct and numerous, may be present even with early growth stages, 

 and may stain more intensely than in P. vivax infections. The mature 

 schizont is usually rather rounded and measures about three-fourths the 

 diameter of the corpuscle. Merogony often produces 8-10, but sometimes 

 as many as 14 merozoites. 



The gametocytes are similar to those of P. vivax and P. malariae and 

 are usually not foimd in oval corpuscles. Enlargement of the corpuscle 

 and the presence of Schiiffner's dots distinguish the gametocytes of P. 

 ovale from those of P. malariae. Since they fill only about three-fourths of 

 the corpuscle, they are distinctly smaller than the gametocytes of P. vivax. 



The mosquito phase'' (Fig. 13.6) 



Although gametocytes establish infections only in the natural 

 hosts, maturation will take place even in vitro. Maturation of the micro- 

 gametocyte (exflagellation) involves nuclear division and budding to 

 form uniflagellate microgametes, the number of which is small — 4-8 in 

 P. vivax (84), 4-8 in P. jalciparum and 2-5 in P. malariae (124), accord- 

 ing to various reports. Exflagellation in vitro can usually be seen within 

 5-20 minutes after withdrawal of blood from a patient. The macrogame- 

 tocyte merely ruptures the enclosing corpuscle and then rounds up. The 

 possible occurrence of meiosis at this stage is suggested by observations 

 of MacDougall (62a). Fertilization is accomplished when a microgamete 

 penetrates the rounded macrogamete. 



The zygote soon becomes an active ookinete which passes through 



^Recent descriptions of the mosquito phase have been published for P. malariae 

 (65) and for P. vivax and P. jalciparum (64). 



