GENERAL ZOOLOGY 



Merogony— merozoites are released, 



infect additional liver cells, and 

 appear for first time in erythrocytes 



Sporozoites enter liver cells 

 or reticulo- endothelial cells 



Repeated merogonic generations in 

 erythrocytes— with release of each 



new generation of merozoites, 

 patient sufifers malarial paroxysm 



Repeated merogonic 



generations in liver and 



reticulo -endothelial cells 



Some merozoites eventually 



become male or female 



gametocytes 



Sporozoites are injected into 



human bloodstream as 



mosquito feeds 



Sporozoites, released from cysts, 



migrate through hemocoel 



to salivary glands 



Gametocytes are ingested 

 by feeding mosquito 



In stomach of mosquito, gametocytes 



become gametes, unite in syngamy 



to form ookinetes 



Ookinetes pass through wall 



of stomach, encyst, and 



undergo sporogony 



Fig. 8.15. Sequence of events in the life cycle of the malaria parasite. 



Malaria and the Malaria Parasite. The disease called malaria has 

 been known since ancient times. Some investigators have regarded it as 

 largely responsible for the decline of ancient Rome. It is certain that both 

 Romans and Greeks, and probably other peoples, suffered greatly from this 

 pestilence. Early explorers of the Americas found it established in the 

 tropical regions of both continents and brought back to Europe the South 

 American Indians' remedy, "peruvian bark" of the cinchona tree, from which 

 quinine was later extracted. Intensive research, stemming largely from the 

 shortage of this natural remedy during the years of World War II, has led to 

 the production of new and more effective synthetic malaricides. The disease 

 is still prevalent and serious, however, in all the warmer parts of the world. 



The word malaria ("bad air") was originally applied to a group of fevers 

 associated with swampy regions. The idea that the air of such a region acts 

 as a causative agent is still prevalent among the ignorant. If there are no 

 mosquitoes to act as intermediate hosts for the parasite, however, there is 

 no malaria. The agents of infection in this instance are Sporozoa, various 

 species of the genus Plasmodium; Plasmodium malariae, for example, produces 

 one form of malaria in man. In the vertebrate host, the parasite lives intra- 

 cellularly in the red blood cells and other cells, where asexual reproduction 



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