TRYPANOSOMA BRUCEI 



93 



second rat, in whose mouth infective flea faeces were placed, became 

 infected in six days. 



When infective forms of T. lewisi have been developed within the 

 gut of a rat flea, they may enter and infect the vertebrate host 

 by 1 (a) being crushed and eaten by the rodent ; (b) the rat may lick 

 its fur on which an infected flea has just passed infective excrement ; 

 or (c) the rat may lick, and infect with flea excrement, the wound 

 produced by the bite of the flea. 



The time taken for the full development of T. lewisi in the flea 

 is about six days. The intracellular phase is at its height about 

 the end of the first day ; the crithidial phase, in the flea's rectum, 

 begins during the second day; the stumpy, infective trypanosomes 

 are developed in the rectum about the end of the fifth day. 



Wenyon 2 writes that, " the fleas, when once infected with T. lewisi, 

 remain infected for long periods, for though many small infective 

 trypanosomes are washed out of the gut at each feed, those that 

 remain behind multiply to re-establish the infection of the hind gut. 

 Further, the infection is still maintained even if the flea is nourished 

 on a human being, so that fresh human blood does not appear to be 

 destructive to the infective forms in the flea." 



The best method of controlling fleas during experiments is that 

 due to Noller. He adopted the method of showmen who exhibit 

 performing fleas, and secure them on very fine silver wire. 



Of fleas fed on an infected rat only about 20 per cent, become 

 infective. About 80 per cent, are immune. If fleas are examined 

 twenty-four hours after feeding, trypanosomes will be found in all, so 

 that many of the parasites are destined to degenerate. 



It may be of interest to note that Gonder 3 (1911) has shown that 

 a strain of T. lewisi resistant to arsenophenylglycin loses its resistance 

 after passage through the rat-louse, Hcematopinus spinulosus. These 

 experiments suggest that physiological " acquired characters " may 

 be lost by passage through an invertebrate host. 



Trypanosoma brucei, Plimmer and Bradford, 1899. 



Trypauosoma brucei was discovered by Sir D. Bruce in 1894 in 

 cattle in Zululand and was named T. brucei by Plimmer and Bradford 

 in 1899 in honour of its discoverer. This trypanosome is of con- 

 siderable economic importance, as it is responsible for the fatal 

 tsetse fly disease, or " nagana," in cattle, horses and dogs. The 

 disease is widely distributed in Africa and is transmitted from host to 

 host by the tsetse, Glossina tnorsitans, and other species of Glossina. 



1 Nuttall, Parasitology , v, p. 275. 



2 Report to Advis. Comm. Trop. Dis. Research Fund, October, 1912, p. 91. See also 

 foiirn. Lond. Sch. Trop. Med., ii, p. 119. 



3 Centralbl. f. BakL> Orig., Ixi, p. 102. 



