Chapter 8 



Protozoa parasitic in the circulatory 

 system (continued) 



Sporozoa 

 Plasmodium 



THE SPOROZOAN parasites of the human blood are all 

 malarial organisms and placed in the genus Plas- 

 modium. Although there are certain morphological dif- 

 ferences which characterize the different species, the gen- 

 eral cycle of development is nearly identical. The malarial 

 organisms of man are transmitted by female mosquitoes 

 belonging to the genus Anopheles. Asexual and sexual re- 

 production takes place in man and mosquito respectively. 

 When an infected anopheline mosquito feeds on man 

 sporozoites are introduced (Fig. 21, 1). The immediate 

 change the sporozoites undergo is unknown. But during 

 about six days after the bite of an infected mosquito, no 

 parasites can be seen in the peripheral blood and quinine 

 has no effect. Judging by what has been observed in early 

 phase of Plasmodium infection in ])irds, it is now supposed 

 that there probably occurs exoerythrocvtic development 

 of the organism. Sooner or later, however, the organisms 

 enter erythrocvtes (Fig. 21, 2) and become schizonts (Fig. 

 21, 3). At the beginning the schizonts are ring-form. They 

 grow in size and finally divide into 12-24 or more mero- 

 zoites (Fig. 21, 4, 5) which are finallv set free in the plasma 

 (Fig. 21, 6). This schizogonv takes place in 48 to 72 hours. 



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