L36 INFECTIOUS DISEASES DUE TO PROTOZOA 



disease is transmissible by inoculation to nearly all mammals, rats 

 and mice being the most susceptible. 



Tr. evansi is a motile trypanosome 20-30 fi in length, including 

 the flagellum, by one to two /x in breadth, somewhat blunt at the 

 posterior end and tapering gradually at the anterior end. The 

 undulating membrane is well defined, beginning at or near the 

 centrosome (blepharoplast) in the posterior 

 portion of the parasite and ending anteriorly 

 in a long, free flagellum. 



The parasites are transmitted by flies, 

 Tabanus tropicus (Rogers), Stomxys calcit- 

 rans, (Curry), possibly other flies and by 

 fleas (Musgrave and Clegg). 



In the majority of cases the parasites are 

 easily found in the peripheral blood. They 

 are usually seen during the febrile periods; 

 but decrease in numbers during the afebrile 

 periods so that a prolonged search may be 

 required or the microscopical examination 

 may even fail to reveal the trypanosomes. 

 The periods during which the parasites are 

 scarce or are not found on microscopical 

 examination vary from one to six days 

 (Lingard); but the blood is virulent as 

 shown by inoculation into susceptible ani- 

 mals. Mice, rats and dogs are the most 

 suitable for inoculation. In mice and rats 

 the parasites are present in the peripheral 

 blood, two to three days after subcutaneous inoculation, 24 hours 

 after intraperitoneal inoculation and increase in numbers till death, 

 which occurs three and one-half to five days after subcutaneous 

 and two and one-half to three days after intraperitoneal inocu- 

 lation. 



Changes in the blood. — There is a progressive diminution in 

 the number of red corpuscles and in the amount of hemoglobin. 

 Smith and Kinyoun state that in a horse sick seven days there 

 were 3,500,000 red corpuscles and 14,500 leucocytes, and in an- 

 other, sick six weeks, 3,200,000 red corpuscles and I :>,!)()() leu- 

 cocytes per cmm. The hemoglobin was slightly diminished, 



Fig. 16. Trypanosoma 

 evansi, rat's blood {Nocht 

 and Mayer). 



