810 



ANIMALS AND THEIR ENVIRONMENT 



dant. The result was a terrible epidemic ol sleeping sickness that killed 

 two thirds ot the population and rendered hirge areas ol land unin- 

 habitable. Today a major activity ol the Uganda government is the 

 gradual reclamation ol its land by systematically killing off all ol 

 tiie large mammals that carry the disease and iniect the tsetse Hies. 



Alrican sleeping sickness begins with lever and headache, loUowed 

 by weakness and anemia. The patient may then recover partially or 

 completely. Olten, however, the trypanosomes reach the central nervous 

 system and then the host becomes progressively less active, repeatedly 

 lalling asleep and abhorring exertion. Emaciation, coma and death 

 ioUow alter several weeks. In South America trypanosomes cause a dis- 

 ease involving lever, anemia and mental disturbances. The parasites 

 are normally lound in small mammals and are transmitted to man by 

 a bloodsucking bug (order Hemiptera). 



Blood Flukes. Blood flukes belong to the lamily Schistosomatidae 

 and iniect birds and mammals. Two characteristics distinguish them 

 from other trematodes: the sexes are separate, and the cercariae pene- 

 trate directly through the skin ol the final host rather than being eaten. 

 Man may be inlected by three species ol the genus Schistosoma (Fig. 

 39.11). Two species live in blood vessels near the digestive tract and 

 their eggs appear in the feces; the third lives in vessels near the bladder 



IN FECES •• 

 S. TT-iansonl S. ja ponicum> 



Eggs 

 in -water 



Miracidia 



Sna.ll hosts 

 IfCercaria -^ 



IN URINE: 

 S. "haematobium 



in. I -water 



Miracidium. 

 i 



Snaiil host 



Figure 39.11. Three species of Schistosotna that infect man. In severe cases (top 

 figure) the body is emaciated and the feet edematous while the spleen is greatly 

 enlarged. Eggs hatch on contact with water and each species enters its own par- 

 ticular kind of snail host. Emerging cercariae penetrate directly into the human skin. 

 In regions where these parasites are prevalent, children usually become infected as 

 soon as they start playing in water. 



