Insects and Disease 



Trypanosoma lewisi, a parasite of rats, is per- 

 haps the best known as it is always common where- 

 ever rats are found. Sometimes as many as 30% or 

 40% of the rats of certain districts are infected. 

 It is thought that these are transmitted from rat to 

 rat by the common rat-louse which serves as an 

 intermediate host. Fleas may also act as dissem- 

 inating agents. 



A few other kinds cause serious disease of ani- 

 mals, but we are more interested just now in the 

 particular one that is causing so much trouble in 

 Africa. This parasite was discovered in 1902 and 

 was named Trypanosoma gambiensi (Fig. 111). 

 Since then it has been found to be widely dis- 

 tributed. Although the natives have doubtless long 

 been subject to the disease caused by this parasite, 

 the recent influx of whites to these regions and 

 the consequent movements of the natives have 

 caused a great spread of the disease so that whole 

 regions are now made desolate, the inhabitants 

 dying or fleeing to escape the uncanny death. 



The disease may run its course in a few months 

 or it may take years. The symptoms are various, 

 but infection is usually soon followed by fevers, 

 sometimes mild, sometimes severe, which recur at 

 irregular intervals. Certain glands or other parts 

 of the body may become swollen. More or less 



