Etiology, Pathogenicity. 



793 



Pathogenicity. The disease may easily.be transmitted to 

 healthy dogs by subcutaneous or intramuscular inoculation of 

 blood containing parasites. These appear in the blood after 2 

 or 5-6 days, and the infected animals usually die in from 3-5 or 

 9-11 days, sometimes however the disease may extend even to 60 

 days, or exceptionally recovery may take place. Other animals 

 are not susceptible to the infection. 



Tenacity. Blood containing piroplasma remains infective for 25 days 

 when kept in a cool and dark place. At summer temperature, however, it becomes 

 inactive after 14 days; the parasites die at 44° C, in I14 hours, at 50° in a half 

 hour. 



In France the natural infection is according to Nocard & 

 Motas transmitted by the Dermatocentor reticulatus (possibly 

 also by the Ixodes ricinus). 

 In South Africa, according 

 to Lounsbury & Eobert- 

 son, by the Haemophysalis 

 Leachi, in India according 

 to Christophers and Nuttall 

 by the Rhipicephalus san- 

 guineus. The two last 

 named species of ticks pass 

 their development as larvae 

 and nymphs on three hosts, 

 possibly also on other ani- 

 mals than dogs. Females 

 which have sucked the blood 

 of healthy dogs transmit the 

 virus by their eggs to the 

 larvae, in which, as well as 

 in the nymphs it remains 

 latent, and only the sexually 

 mature ticks are capable of 

 again transmitting the piro- 

 plasma to dogs (Lounsbury, 

 Theiler), whereas the infec- 

 tion does not succeed with 

 mature ticks taken from affected dogs. Ticks capable of infec- 

 tion may carry virulent piroplasma in their bodies even for 

 seven months, and transmit them in the meantime to dogs 

 (Nuttall). 



Young dogs are much more susceptible to the infection than 

 adults. 



It is questionable whether the piroplasma of dogs are identical in different 

 parts of the world. MacPadyean and Nuttall found dogs, which had recovered from 

 the piroplasmosis of India, to be still susceptible to infection with the African para- 

 sites. 



Anatomical Changes. The autopsy of dogs dead with the 

 disease shows pronounced acute swelling of the spleen, with a 

 dark, bluish-red, somewhat soft pulp, hyperemia of the liver, 



Fig. 139. Fever curve in piroplasmosis of 

 dogs. After subcutaneous injection of viru- 

 lent blood ; two-months-old dog ; fatal termi- 

 nation. (After Wetzl. ) 



