THE PARASITE OF MAL DE CADERAS 815 



precedes epizootics of Mai de caderas and that among rats which precedes epidemics 

 of plague. Lignieres has infected rats with Mai de caderas by inoculating them 

 with fleas crushed in salt solution (Nabarro's translation of Laveran and Mesnil's 

 " Trypanosomes ").] 



Morphology of the parasite. Trypanosoma equinum was discovered by 

 Elmassian [in Paraguay in 1901]. In fresh preparations it is morphologically 

 indistinguishable from T. brucei and T. evansi ; in stained preparations how- 

 ever the characters of the centrosome differentiate it clearly from allied 

 parasites. 



The centrosome is very small, and since it stains like the flagellum it is 

 difficult to distinguish. [In trypanosomes of the type T. evansi, on the other 

 hand, the centrosome is very obvious and measures about 0'5/>t and stains 

 deep purple (Laveran and Mesnil).] 



T. equinum measures 22-24/x long by about 1'5/* broad. It multiplies 

 like T. brucei by binary longitudinal fission. 



Agglomeration in the blood, which is favoured by the addition of normal 

 sheep, pig or horse serum and particularly of serum from bovines, sheep or 

 pigs infected with caderas, gives rise to rosette forms in which the posterior 

 ends are in apposition. 



The number of trypanosomes in the blood of infected Equidse varies at different 

 periods of the disease. In the early stages the parasites are very scanty but as 

 death approaches they become more numerous ; they are not however constantly 

 present in the blood in the course of the naturally contracted disease, and there are 

 times when no parasites can be found. Trypanosomes are found when the tem- 

 perature of the animal rises above 38 C. but disappear when it reaches 41 C. 

 (Elmassian and Migone). 



Vitality. In blood kept at the ordinary temperature Trypanosoma equinum 

 dies rapidly but if the blood be kept in the ice chest the parasite will live for 

 3 days. The addition of normal serum (fowl, horse, sheep, rat or bovine) to 

 the blood lengthens the life of the parasite by from 5-11 days. 



[Cultures. Laveran and Mesnil failed to grow T. equinum on blood-agar 

 at room temperature. Thomas and Breinl using a modification of Novy and 

 M'NeaPs medium chicken-broth-rabbit-blood agar grew a T. equinum 

 from rabbits' blood at 22 C. and infected a rat after 29 days' incubation : 

 sub-cultures failed.] 



Experimental inoculation. Horses, mules, asses, monkeys, mice, white 

 rats, guinea-pigs, rabbits and dogs are all susceptible to experimental infec- 

 tion. No symptoms are produced in sheep, cattle and pigs, but the blood of 

 these animals remains infective for mice for about 2 months after inoculation. 

 Birds are immune. 



Human serum has a specific action on animals infected with Caderas 

 (Laveran and Mesnil). Laveran was able to cure 10 per cent, of mice experi- 

 mentally infected by inoculating them with human serum. 



Sheep, goats, bovines and pigs which have recovered from an infection 

 with T. equinum are immune and their serum has for a short time some 

 slight prophylactic property. 



Specific nature of Mai de Caderas. Caderas can be differentiated from 

 other Trypanosome infections by a study of the immunity reactions. Dogs 

 which have recovered from an infection with the parasite of dourine and 

 which are therefore immune to that disease are as susceptible to Caderas as 

 normal dogs (Lignieres). A goat and a sheep cured of and immune to Nagana 

 were just as susceptible to Caderas as normal control animals. The serum 

 of animals cured of Nagana has no action on T. equinum (Laveran and 

 Mesnil). 



