ETIOLOGY 



401 



of this country; being far more prevalent in those parts where 

 iioods and inundations occur than in the higher and dryer 

 portions" (Pease). If the identity of surra with tsetse- fly 

 disease proves to be true, which is still questioned, it has a 

 wide distribution in Central Africa. 



Surra does not exist in the United States, but because of 

 its prevalence and long standing in the Philippines it is liable 

 to be introduced into this country. For this reason its nature 

 should be understood by American veterinarians. 



§ 312. Etiology. There is little or no doubt that surra 

 is due to the presence in the blood of a flagellated infusorian, 

 Trypanosoma Evansi. 



"A motile trypanosoma 20 to 30 /( in length to i to 2 ;U in breadth, 

 somewhat blunt at the posterior end and gradually tapering at the 

 anterior end. The undulating membrane is well defined, beginning at 

 or near a small body (centroscme) in the posterior portion of the para- 

 site and extending forward as a free flagellum. It is provided with a. 

 nucleus and a granular protoplasm." 



This organism is invariably found during the paroxysms 

 of the disease in the blood of animals which have acquired 

 surra either naturally or experimentally. Although blood 

 containing these infusoria readily communicates the disease to 

 susceptible animals it entirely loses its virulence when it is 

 filtered through porcelain, so as to free it from the parasite. 

 The disease can be transmitted to healthy, susceptible animals 

 even of different species with the unfiltered blood of a diseased 

 animal. The microscope reveals the infusoria in vast numbers 

 moving with great activity in the blood. When this acute 

 stage has passed the organisms disappear, the temperature 

 falls, the severity of the symptoms abates, and there is an 

 intermission, during which, at the beginning of the attack, the 

 patient may appear in good health. Although the blood dur- 

 ing an intermission may appear under the microscope to be 

 absolutely free from the parasites, its inoculation into suscep- 

 tible animals will, as a rule, produce the disease. The blood 

 of surra affected horses loses its power of transmitting the dis- 

 ease by inoculation ia about eighteen hours after death. 



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