PARASITIC PROTOZOA 355 



regions where it occurs, is caused by Trypanosoma evansi and 

 is probably transmitted by the bites of stable-flies (Stomoxys) 

 and horse-flies (Tabanida). 



In 1906 some cattle that had been imported into America 

 from India for experimental purposes were found to be in- 

 fected by the parasite which causes this disease. Fortunately 

 this discovery was made while the cattle were still in quaran- 

 tine. All those infected were destroyed and the disease thus 

 stamped out before it had a chance to spread. A disease 

 similar to both nagana and surra, and known as murrina, has 

 recently been found affecting horses and mules in Panamas. 

 It is caused by Trypanosoma hippicum. It is believed that the 

 parasite is carried mechanically from one host to another by 

 flies that visit the sores due to wounds of various kinds on the 

 animals. 



Dourine, or mal du coit, is a serious disease of horses that 

 has been introduced into North America, where it appears from 

 time to time in widely separated parts of the west. It is caused 

 by Trypanosoma equiperdum, and is transmitted during breed- 

 ing, perhaps rarely by bites of flies or fleas. As soon as infect- 

 ed animals are discovered they are destroyed, and the disease 

 is now almost or quite stamped out. Trypanosoma equinum 

 causes a deadly disease of horses, known as mal de caderas, in 

 Brazil and other parts of South America. 



Several other species of trypanosomes are found in wild and 

 domestic animals. Almost any of these may at any time be- 

 come of more or less economic importance when susceptible, 

 non-immune animals are brought into the regions where the 

 parasites occur, or when the parasites by some means are 

 introduced into new regions. 



RELAPSING FEVERS AND OTHER DISEASES CAUSED BY 

 SPIROCH,ETES 



The spirochsetes are very minute, thread-like parasites 

 closely related to the trypanosomes. They occur in shellfish 

 and in the alimentary canal or blood of certain fish, birds and 

 mammals where they apparently do no harm, but some 



