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Dr. H. L. Duke. Antelope as a [Apr. 20, 



dismissed, owing to the fact that other species of trypanosomes can produce 

 similar symptoms in these animals. The point of practical importance to be 

 established is whether these trypanosomes are pathogenic to man, and this is 

 obviously very difficult to prove. 



In a recent paper I have discussed the differential diagnosis of trypanosomes 

 recovered from the Lake-shore and T. hrucei. The recent discovery that 

 T. rhodesiense is susceptible to the action of human serum is of great interest 

 in this connection, since on theoretical grounds alone a trypanosome which 

 succumbed to human serum in vitro and in laboratory animals might well 

 be judged non-pathogenic to man. In the present instance it must be borne 

 in mind that, although these Lake-shore trypanosomes, whether found in wild 

 flies or in wild antelope, may have been originally derived from human beings 

 during the recent epidemic, it is possible that the prolonged sojourn in other 

 hosts may have materially modified the reactions of the original " Uganda " 

 strain. 



Apart from its pathogenicity to man, there is little in the behaviour of 

 T. rhodesiense to suggest close affinity to T. gamhiense. Its recently discovered 

 susceptibility to the action of human serum, together with many of its 

 animal reactions, suggest rather resemblances to T. brucei. This latter 

 trypanosome has up to the present time been generally considered to be non- 

 pathogenic to man. The mere fact, however, that T. rhodesiense was originally 

 recovered from man is sufficient to account for the controversy which has 

 arisen over the attempt to separate this trypanosome from T. gamhiense. 



In the same way with these Lake-shore trypanosomes. Whatever be the 

 scale of virulence established, the final diagnosis will always depend upon the 

 behaviour of the organism in the human subject. 



In reviewing the above experiments it will be seen that these antelope are 

 apparently very slowly losing their infectivity for T. gamhiense. The animals 

 are all in excellent health, and in two out of four cases the most recent 

 evidence has been afforded by positive laboratory-bred G. palpalis. It would 

 thus seem that the adaptation of T. gamhiense in these antelope approaches 

 very nearly the biological ideal, i.e., a compromise between the trypanosome 

 and its host, whereby, without injuring the latter, the parasite becomes 

 peculiarly well equipped to survive in the insect carrier. 



Time alone can show whether this balance between parasite and antelope 

 host can be maintained indefinitely. Judging from the case of Bushbuck 2371 

 it is quite reasonable to expect evidence of infectivity to crop up occasionally 

 at long intervals in these laboratory animals. Surrounded by wild flies in 

 nature such an antelope as 2371 might well prove a far greater danger than 

 would appear from the long intervals occurring between positive experiments 



