890 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



ILEMOSPORIDIA (Danilewsky emend. Schaudinn) 



The most important parasites of this order are those, belonging to 

 the Genus Plasmodium, which cause malaria in man. Organisms 

 similar to these are parasitic in the red blood cells of apes, bats and 

 antelopes. Proteosoma and Hamoproteus are two genera parasitic 

 in the red blood cells of birds. It was the study of these avian 

 parasites which led to the discovery of the way in which malaria is 

 transmitted by the bite of the mosquito. 



PLASMODIUM (Marchiafava and Celli, 1885) 



At least three species of this genus are parasitic in man: Plasmodium 

 vivax (Grassi and Feletti), the cause of tertian malaria, Plasmodium mal- 

 aria (Laveran), causing quartan malaria, and Plasmodium falciparum 

 (Welsh), which causes aestivo-autumnal malarial fever. 



MALARIA 



Malaria is a disease caused by an amoeboid parasite of the red blood 

 corpuscles. It is transmitted by the bite of anopheline mosquitoes 

 in which the parasite has completed the sexual cycle of its development. 



It exists in all parts of the tropical and subtropical world (Fig. 189). 



A young malarial parasite or sporozoit, derived from the mosquito enters a red cell 

 and supports itself by living upon the cell's substance. The parasite grows, proceeds 

 to multiply asexually and divides into a number of merozoites which are set free 

 by the rupture of the red cell. Those of the merozoites which escape ingestion by 

 the white cells of the blood enter red cells where they may again multiply asexually, or 

 they may develop into sexual forms. When blood, containing malarial parasites, is in- 

 gested by a suitable mosquito, all the parasites, except the adult sexual ones, are di- 

 gested and die. Soon after they are ingested, the macrogametocyte extrudes polar 

 bodies and becomes a macrogamete and the microgametocyte produces several micro- 

 gametes, one of which enters and fertilizes the macrogamete. Through the fusion of 

 macrogamete and microgamete a copula is formed, which since it is motile is called an 

 ookinet. This makes its way until it comes to lie just beneath the outer surface of 

 the mosquito's stomach. There it develops, as an oocyst, until it reaches several 

 times its original size. It divides into a number of areas, or sporoblasts, each of 

 which subdivides to form many very small, hair-like sporozoites. When the oocy?t 

 bursts, some of the sporozoites pass forward to find their way into the salivary 

 glands of the mosquito, and, when it bites, they are extruded, with the saliva, into the 



