70 



COLLEGE ZOOLOGY 



succeed in making their way to the mos- 

 quito's sahvary glands. The next time the 

 mosquito takes a blood meal, sporozoites 

 are injected into the human body. 



Adequate control of human malaria in- 

 volves at least three approaches: 



1. Treatment of infected humans by use of 

 appropriate antimalarial drugs. 



2. Protection of uninfected individuals by use 

 of screens, nets, gloves, and the application 

 of solutions to the skin which are capable 

 of repelling the mosquito. 



3. Elimination of the mosquito, either by use 

 of insecticides such as DDT, or by drainage 

 and other engineering operations calculated 

 to destroy its breeding places. 



Because of control measures, malaria is 

 no longer an endemic disease in the United 

 States. In 1951 the National Malaria Society 

 went out of existence because its goal had 

 been attained. This was certainly a remark- 

 able achievement in public health history. 



Other blood and 

 tissue parasites 



Blood- and tissue-inhabiting forms are 

 found among the flagellates. Two important 

 types are ( 1 ) the trypanosomes and ( 2 ) the 

 leishmanias. 



The genus Trypanosoma is widespread in 

 nature and may be found in the blood of 



Figure 34. Trypanosoma gambiense, the parasitic flagellate of African sleeping sickness in man. 

 Form on left, stage in man; and form on right, stage in the tsetse fly. Highly magnified. 



many common mammals, birds, reptiles, 

 fishes, and amphibians. Man is host to three 

 well-known species: Try^panosoma gam- 

 biense (Fig. 34); Trypanosoma rhodesiense, 

 which causes two forms of African sleeping 

 sickness; and Trypanosoma cruzi, the causa- 

 tive agent of Chagas' disease, which occurs 

 in Central and South America. 



African sleeping sickness is transmitted by 

 the bite of both sexes of the tsetse fly. When 

 an infected insect takes its blood meal, the 

 slender, flagellated trypanosomes pass by 

 way of the fly's proboscis into the human 

 host. Early stages of the disease are charac- 

 terized by fever and swelling of the lymph 

 glands in the neck. Involvement of the nerv- 

 ous system results progressively in drowsi- 

 ness, coma, emaciation (through inability 



to take food), and finally death. Treatment 

 with naphuride, tr}'parsamide, or pentami- 

 dine is fairly successful, especially if the pa- 

 tient is reached early in the course of the 

 disease. Recent experiments with antrycide 

 give promise of dramatic results in the treat- 

 ment of tr}'panosomiasis in Africa. The 

 prevalence of sleeping sickness has greatly 

 hindered the development of natural re- 

 sources in many of Africa's richest tropical 

 areas. In rare instances the infection has 

 been known to be transmitted by sexual 

 contact. 



South American trypanosomiasis or 

 Chagas' disease behaves quite differently. 

 Only the acute stages are serious, and gen- 

 eral involvement of the nervous system does 

 not take place. The trypanosomes are trans- 



