42 



THE HEMOFLAGEUATES 



in that the undulating membrane lies in a 

 long reservoir which runs the whole length 

 of the body and opens at the anterior end, 

 whereas in Trypanosoina the reservoir is 

 very short and opens laterally near the 

 posterior end so that the undulating mem- 

 brane runs along the side of the body 

 (Clark, 1959). 



Members of the genus Phylomonas 

 are heteroxenous in the latex of plants and 

 hemipterous insects, passing thru lepto- 

 monad and leishmanial stages in their life 

 cycle. They are found in milkweeds and 

 related plants, and cause the normally 

 milky sap to become colorless. 



The only genera parasitic in domestic 

 animals and man are Trypanosoma and 

 Leishmania. Since, however, their 

 stages in the invertebrate vector are mor- 

 phologically similar to those of the genera 

 confined to invertebrates, one cannot be 

 positive, when he finds an infected inver- 

 tebrate, whether it is infected with a para- 

 site of vertebrates or with one of its own. 

 It is possible, too, that some of the forms 

 which we now think are confined to inverte- 

 brates may actually be normal parasites 

 of some wild vertebrates. 



make it practically impossible to raise 

 livestock in many parts of the tropics 

 which would otherwise be ideal. Accord- 

 ing to Hornby (1949), "Trypanosomiasis 

 is unique among diseases in that it is the 

 only one which by itself has denied vast 

 areas of land to all domestic animals 

 other than poultry. The areas of complete 

 denial are all in Africa and add up to per- 

 haps one quarter of the total land surface 

 of this continent. " Some, but not all, of 

 the African species are transmitted by 

 tsetse flies. These flies occupy almost 

 4 million square miles, an area larger 

 than the United States, and this whole re- 

 gion is under the threat of trypanosomosis. 



In a recent Hollywood epic on South 

 African history, there is a scene in which 

 a line of Boer covered wagons on the Great 

 Trek to the north is attacked by Zulus. 

 The warriors pour over the hills, the wag- 

 ons form a circle with the women and chil- 

 dren in the center, and the Boer men pre- 

 pare to fight. It is just like a scene from 

 the American Wild West, with the Indians 

 attacking a wagon train of pioneers. But 

 there is one difference- -the Zulus had no 

 horses, and made their attack on foot. 

 The reason? Trypanosomosis. 



Genus lITfPANOSOmA Gruby, 1843 



Members of this genus occur in all 

 classes of vertebrates. They are para- 

 sites of the circulatory system and tissue 

 fluids, but some, such as T. cruzi, may 

 actually invade cells. Almost all are 

 transmitted by blood-sucking invertebrates. 

 Most species are probably non-pathogenic, 

 but the remainder more than make up for 

 their fellows. 



Trypanosomosis is one of the world's 

 most important diseases of livestock and 

 man. Trypanosomes cause African sleep- 

 ing sickness and Chagas' disease in man 

 and a whole series of similar diseases in 

 domestic animals. They are relatively 

 unimportant in North America, but they 



A large number of species of Trypano- 

 soma has been named. At one time it 

 was customary, and still is to some extent, 

 to give different names to trypanosomes 

 from different hosts. Many of these names 

 are still valid, but as we learn more and 

 more about the host-parasite relations and 

 epidemiology of the trypanosomes, many 

 other names have fallen into synonymy. 

 No attempt will be made here to list all 

 the synonyms of each species, but the more 

 important ones will be mentioned. 



Trypanosomes are classified in groups 

 on the basis of their morphology, life cy- 

 cles and other biological characteristics. 

 The validity of this grouping is shown by 

 the fact that their metabolic characteris- 

 tics, which vary widely, fall into the same 

 groups. 



