AFRICAN TRYPANOSOMIASIS 133 



Carriers. 



The Glossina palpalis. It inhabits wooded shores of rivers and 

 lakes. 



Although the shores of Lake Victoria Nyanza, the banks of the 

 Nile and other rivers swarmed with these tsetses before 1898, they only 

 became infected with trypanosomes about this time. Consequently 

 one concludes that the infection was brought by Emir Pasha's men 

 from the Belgian Congo. 



Thirty per cent, of the natives working for the Government (one 

 month yearly, at Entebbe in Ugand^ in lieu of hut tax) were infected 

 with these trypanosomes in 1903. The hut-tax labourers were removed 

 from the lake shores, and one year later the flies infected with this 

 parasite fell from 11 '2 per 1,000 to i'2 per 1,000. 



In 191 2, as the lake shores became more deserted, it had fallen to 

 o'i4 per 1,000. Hence man in the A'icinity means more flies infected. 

 A fly may remain infective for several months. 

 Man is bv no means the only source of the virus. 

 Tsetses can convey the infection for some fifty days after the fly 

 has fed on an infected animal (Kleine). 



An infected flv mav and does infect susceptible creatures bitten on 

 the first bite. 



Cycle of Development. 



The cvcle of development of the T. gambiense in the G. palpalis 

 is as follows : — 



Laboratory flies when fed on infected animals become infective in 

 an average of thirty-six days, extremes twenty-seven to fifty-three days. 

 Of those tsetses allowed to feed on infective animals, only o'5o per 

 cent, become infective. 



When in test-tubes the trypanosomes seem to die off, but after 

 twenty davs a resistant strain appears which soon multiplies by 

 myriads. 



Manv flies become infected, but few become infective, e.g., try- 

 panosomes partially develop in many, but go on to completion in but 

 few tsetses. It was found that 2 per cent, became infected, but only 

 o"5 per cent, infective. 



For the first three to four days after the Glossina^ have fed on 

 infected blood, trypanosomes are found in all, these being the try- 

 panosomes originally ingested with the blood. In six to seven days, 

 when digestion is completed, most have disappeared from the tsetse, 

 except in from 2 per cent, to 8 per cent, of those infected. In the 

 remainder, say about 5 per cent., the trypanosomes develop, increase, 

 and fill the whole of the gut, fore, mid and hind gut, with swarms of 

 multiplication forms. 



