370 EQUINE MALARIA 



§ 282. History. The disease appears to have been first 

 described by Wiltshire in 1883. Guglielmi discovered the 

 parasite of this affection in 1899, and Rickmann found it in a 

 large number of horses that died of "horse sickness." A 

 good description of this affection was given by Theiler in 1901. 



§ 283. Geographical distribution. This disease 

 appears to be very largely restricted to Southern Africa and 

 Europe. The disease known as malarial fever in the United 

 States has not been demonstrated to be due to a piroplasma. 

 Peters describes this disease in horses in the. West but he did 

 not find its specific parasite. 



§ 284. Etiology. Laveran who has studied this affection 

 states that its cause is Piroplasma equi. It is closely related 

 to P. bigeminum. It measures from 0.5 to 2.0 )x. During the 

 invasion and multiplication of the parasites there is a high 

 temperature. In the blood corpuscle the parasite is single, in 

 pairs or in rosette form. The disease was believed not to be 

 transmitted directly with the blood containing the parasite. 

 Theiler, however, succeeded in proving that equine piroplas- 

 mosis is inoculable with the blood of immune horses into sus- 

 ceptible ones. The natural method of infection is not known, 

 but it is believed by many to be by means of a tick. 



Theiler's conclusions relative to the transmissibility of 

 this parasite are as follows : 



(i) The piroplasma found in the mule and the donkey 

 is identical with the piroplasma equi first found in the horse. 



(2) The disease caused by this piroplasma is inoculable 

 with blood of immune animals into susceptible ones belonging 

 to the domesticated species of the genus equus. 



(3) The horse shows the greatest susceptibility for this 

 piroplasma ; the donkey is less, and the mule the least, 

 susceptible. 



(4) The possibility of a practicable inoculation against 

 the piroplasmosis stands in the reverse order of the suscepti- 

 bility. The mule may be safely inoculated with immune 



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