432 VETERINARY BACTERIOLOGY 



The pig, sheep, goat, and ox may show transitory symptoms, but 

 are highly refractory. 



Character of Disease and Lesions. The disease differs from surra 

 and nagana in the almost complete absence of edema, and is charac- 

 terized by a paralysis of the hindquarters. There is a progressive 

 emaciation, fever, and the hindquarters become weak; the horse 

 in walking scarcely raises the hoof above the ground. Finally, 

 the animal supports itself by leaning, or falls to the ground. 

 There are no lesions upon the genital organs. 



Immunity. No method of practicable immunization against 

 the organism has been developed. 



Bacteriological Diagnosis. The organism may be found in the 

 blood, particularly during the fever paroxysms. 



Transmission. The disease is evidently endemic in certain 

 parts of South America in rodents or other animals. One of these, 

 the capybara (Hydrochcerus capybara), has been found to be in- 

 fected, and it is said that stockmen can sometimes foretell an out- 

 break of the mal de caderas by the death of many of these animals 

 in the vicinity. The method of transmission is not certainly 

 known. Flies have been supposed to act as carriers, but definite 

 proof is lacking. 



Trypanosoma dimorphon 



Diseases Produced. Gambian horse sickness, trypanosomiasis 

 in horses and other equines, cattle, sheep, and goats. 



Button and Todd, in 1902, reported the discovery of a specific 

 trypanosome in a disease of horses in Senegambia. The same, or 

 very similar trypanosome, has since that time been reported from 

 many African localities in other animals as well. 



Distribution. Various localities in Africa (French Guinea, 

 Zanzibar, Sierra Leone, Mozambique, Zululand). 



Morphology. The organism is characterized by the absence of a 

 free flagellum, the flagellum terminating with the undulating mem- 

 brane. It is dimorphic, some of the cells being 20 to 25 u in length, 

 others only about 12 /w. Transitional forms between these ex- 

 tremes may be found. The undulating membrane is not well 

 developed. Protoplasmic granules are very rare or are absent in 

 the cell. 



Pathogenesis. Experimental Evidence. The disease has been 



