336 PARASITES OF THE DOMESTIC ANIMALS 



paralysis of the hind limbs starts to appear, it usually progresses rapidly, 

 the horse goes down, is unable to rise, and dies in a short time from 

 nervous exhaustion." 



Control. — As dourine is transmitted and spread only by copulation, 

 its eradication is a less difficult problem than in trypanosomiases which 

 may be carried by flies. So little benefit is to be derived from medicinal 

 treatment that in this country, where the disease has appeared only 

 in restricted areas, it is not advisable. While cure may b,e possible, 

 an apparently cured animal may carry the trypanosomes for months 

 in the sexual organs, and relapses are likely to occur. In areas where 

 the disease appears measures of eradication must be based upon the 

 prevention of infected animals from breeding. 



To confine the losses to the minimum, therefore, the prompt castration 

 of affected stallions and the destruction of diseased mares is essential. 

 Spaying of such mares is not a sufficient precaution from the fact that 

 they may be sold and an attempt made to breed them, thus infecting 

 the stallion and through this source spreading the disease. Restrictions 

 in the movement of horses in infected districts and frequent reinspection 

 are further state and federal measures for confining an outbreak so far 

 as possible to its original limits. 



Trypanosoma americanum. — This trypanosome is found in cultures 

 of blood from healthy American cattle. It deserves mention here on 

 account of its common occurrence, though it appears to be harmless. 

 A report by Crawley upon his extended study of this organism will be 

 found in Bureau of Animal Industry Bulletin No. 145 (1912). 



Class III. Sporozoa 



Protozoa (p. 311). — The Sporozoa are all parasitic. Though without 

 motile organs, they are capable of moving from place to place, in some 

 cases by means of pseudopodia. Reproduction is mainly by spore 

 formation, either asexual or sexual. There are a number of forms, 

 however, in which simple reproduction occurs, and the group comprises 

 organisms with life histories as yet not fully known. The Sporozoa, 

 therefore, is a division to be regarded as provisional, containing at pres- 

 ent organisms which when their life histories are fully made out may 

 be more accurately placed with other divisions of the Protozoa. 



Based upon the belief that the Sporozoa are polyphyletic; that is that 

 all have not the same ancestral history, they have been placed in two 

 divisions, — Telosporidia and Neosporidia, the former regarded as 

 descended from the flagellates, the latter from the rhizopods. Of the 

 Telosporidia but two orders are to be considered here, — Coccidia and 

 Hemosporidia. The Neosporidia has one order, — Sarcosporidia, con- 

 taining parasites of domestic animals. 



