I 



OJI 



CHAPTER 7 



Relations of 



Protozoa 



to Man 



-T is obvious to anyone that the larger ani- 

 mals, such as cattle, pigs, horses, and dogs, 

 are important to the human economy and 

 health, but the relation of the minute Pro- 

 tozoa to the well-being of man is not so 

 evident. Nevertheless, protozoans play an 

 important role. They exist in large numbers, 

 but of greatest interest to us are those that 

 live as parasites in the bodies of man and 

 other animals; those that render water unfit 

 to drink, fertilize the soil; and those that 

 have built up large parts of the earth's crust 

 with their skeletons. 



PROTOZOA PARASITIC 

 IN MAN 



Approximately 15 different species of 

 Protozoa have been found living as parasites 

 within the human body. While the majority 

 of these have relatively little effect upon 

 their hosts, certain species cause some of the 

 worst diseases in man. This is especially true 

 in tropical areas where millions of people 

 die each year as a result of protozoan infec- 

 tions. As a matter of convenience, the proto- 

 zoan parasites of man may be divided into 

 two general groups: (1) those which inhabit 

 blood and tissue and (2) those found in the 

 digestive tract and related cavities and pas- 

 sages. 



Blood and tissue Protozoa 



Of the blood and tissue parasites, the 

 human malarial organism is by far the most 

 important. Large numbers of people die 

 from malaria each year, and the enfeebled 

 condition of those chronically ill from the 

 disease represents a tremendous economic 

 loss where malaria control is neglected or 

 haphazardly carried out. 



Although malaria is probably the most 

 devastating disease, with regard to preva- 

 lence, mortality, sickness, and economic loss, 

 it appears to be coming under control. If 

 malaria were finally licked, it would be due 



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