2i6 Arthropods as Essential Hosts of Pathogenic Protozoa 



While the disease is peculiarly African there are a number of 

 instances of its accidental introduction into temperate regions. 

 Slaves suffering from it were occasionally brought to America in 

 the early part of the last century and cases have sometimes been 

 imported into England. In none of the cases did the disease gain a 

 foothold or spread at all to other individuals. 



In 1902 Button described a trypanosome, T. gambiense, which he 

 and Forde had found the year before in the blood of a patient suffer- 

 ing from a peculair type of fever in Gambia. In 1902-1903 Castel- 

 lan! found the same parasite in the cerebro-spinal fluid of sleeping- 

 sickness patients and definitely reported it as the causative organism . 

 of the disease. His work soon found abundant confirmation, and 

 it was discovered that the sleeping sickness was but the ultimate 

 phase of the fever discovered by Button and Forde. 



When Castellani made known his discovery of the trypanosome 

 of sleeping sickness, Brumpt, in France, and Sambon, in England, 

 independently advanced the theory that the disease was transmitted 

 by the tsetse-fly, Glossina palpalis. This theory was based upon the 

 geographical distribution and epidemiology of the disease. Since 

 then it has been abundantly verified by experimental evidence. 



Fortunately for the elucidation of problems relating to the methods 

 of transfer of sleeping sickness, Trypanosoma gambiense is patho- 

 genic for many species of animals. In monkeys it produces symptoms 

 very similar to those caused in man. Bruce early showed that 

 Glossina palpalis "fed on healthy monkeys eight, twelve, twenty-four 

 and forty-eight hours after having fed on a native suffering from 

 trypanosomiasis, invariabty transmitted the disease. After three 

 days the flies failed to transmit it." In his summary in Osier's 

 Modem Medicine, he continues "But this is not the only proof that 

 these flies can carry the infective agent. On the lake shore there 

 was a large native population among whom we had found about 

 one-third to be harboring trypanosomes in their blood. The tsetse- 

 flies caught on this lake shore, brought to the laboratory in cages, 

 and placed straightway on healthy monkeys, gave them the disease 

 in every instance, and furnished a startling proof of the danger of 

 loitering along the lake shore among those infected flies." 



As in the case of nagana, Bruce and most of the earlier investi- 

 ' gators supposed the transmission of the sleeping sickness trypano- 

 some by Glossina palpalis to be purely mechanical. The work of 

 Kleine (1909) clearly showed that for Trypanosoma gambiense as 



