32 



Insects and Disease 



probably identical with Texas fever, occur in other 

 parts of the world where the losses are sometimes 

 appalling. Horses, sheep, dogs, and other animals 

 are also affected with diseases caused by the same 

 group of Protozoan parasites. Most of them have 

 been shown to be transmitted by various species of 

 ticks (Fig. 17) so that from an economical stand- 

 point these little pests are becoming of prime im- 

 portance. Not only do they transmit the disease 

 germs that infect domestic animals but they are 

 known to be responsible for at least two diseases 

 of men, Rocky Mountain spotted fever and the 

 relapsing fevers. 



Spotted Fever. The first of these is a disease that 

 for some years has been puzzling the physicians in 

 Idaho and Montana and other mountainous states. 

 A few years ago certain observers recorded finding 

 Protozoan parasites in the blood of those suffering 

 from the disease, and although more recent in- 

 vestigations have failed to confirm these particular 

 observations it is now quite generally believed that 

 the disease is caused by some such parasite and that 

 the organism is transferred from one host to an- 

 other by certain species of ticks that live on wild 

 mammals of the region where the disease exists. 

 Dr. H. T. Ricketts, who has made a special study 

 of the disease, has shown : 



