582 The Blood Flagellates 



Sandflies are found throughout the year in the tropics. In the cooler 

 climates, the adults apparently do not live through the winter. Instead, 

 hibernation presumably occurs in the last larval instar. The control of 

 sandflies by widespread attacks on breeding places is not, for obvious 

 reasons, a practical method of control. However, the use of residual DDT 

 sprays on suspected shelters and breeding places has produced striking 

 results on a limited scale (27). Similar treatment of buildings with DDT 

 is an effective protection (28). In addition, sleeping nets, fine-mesh screen- 

 ing and insect repellents are useful in preventing contact of sandflies 

 with human beings. 



The importance of animal reservoirs is uncertain. Natural infections 

 with flagellates resembling L. donovani have been reported in dogs, cats, 

 horses, and sheep. L. tropica also occurs naturally in dogs, and the canine 

 strain is infective for man (6). Certain rodents (gerbils, sousliks), found 

 infected in Middle Asia (U.S.S.R.), also may serve as reservoirs (32). Al- 

 though these lower mammals obviously are reservoirs, it is not known 

 how extensive a part they play in the maintenance of endemic leish- 

 maniasis. 



TRYPANOSOMIASIS 



Species of Trypanosoyna are found in fishes, amphibia, reptiles, 

 birds, and mammals, and the great majority appear to be non-pathogenic 

 in their natural hosts. The trypanosomes of mammals include a few 

 pathogens, such as T. briicei of nagana, T. equinum of mal de caderas, 

 T. eqiiiperdum of dourine, T. evansi of surra, and the types which attack 

 man — T. cruzi of Chagas' disease, and T. gambiense and T. rhodesiense 

 of sleeping sickness. Life cycles and methods of transfer differ within this 

 small group. Metacyclic, or infective, stages of T. cruzi develop in the 

 hindgut ("posterior station") of the vector and are deposited on the skin 

 of the vertebrate by a visiting insect. The flagellates may become estab- 

 lished in the vertebrate if they reach a mucous membrane or a break in 

 the skin. Such species as T. cruzi and the non-pathogenic T. lewisi are 

 probably the most primitive of the mammalian trypanosomes, since the 

 invertebrate phase of the cycle resembles that of the presumably ancestral 

 herpetomonad flagellates. Metacyclic stages of T. gambiense, T. rhode- 

 siense, and T. brucei develop in the salivary glands of the vector and are 

 transferred to the mammalian host by inoculation. On such bases, these 

 species are believed to be more highly evolved than the T. lewisi group. 

 Mechanical transfer by tabanid and stomoxid flies is characteristic of T. 

 evansi and T. equinum, which are apparently related to the T. brucei 

 group. Differentiation of these species may have followed their introduc- 

 tion into regions free from their natural vectors. Such a possibility is not 

 too remote, because mechanical transfer of T. gambiense is considered 

 possible for a short time after the flagellates are ingested by the insect 



