506 



nORSEPOX — EQUINE VARIOLA. 



Synonyms: Variola equina — Pustular Grease— PJily ctenoid Rerpes. 



Bejinition. — The liorsepox is a specific infectious fever of the liorse 

 attended by an eruption of pustules or pocks over any part of the sliin 

 or on the mucous membraues lining the various cavities in the body. 

 When the eruption takes place on the mucous membrane of th.e re- 

 spiratory tract it produces an irritation and discharge of matter which 

 greatly resembles that of strangles. This disease was for a long time 

 confounded with the latter disease, and there is no doubt that many 

 light cases in which the eruption is not well marked are still mistaken 

 for distemper. 



The horsepox was described by the early Eoman agricultural writers 

 and by the veterinarians of the last century. It received its first im- 

 portant notice from the great Jenuer, who confounded it with grease in 

 horses, as animals with this disease are very apt to have the eruption 

 of variola appear on the inflamed fetlocks if they are affected with 

 grease at the same time. He saw these cases transmit the disease to 

 cattle in the byres and to the stablemen and milkmaids who attended 

 them, and furnish. the latter with immunity from smallpox, which led 

 to the discovery of vaccination. The horsepox is again frequently 

 mistaken for the exanthemata attending some forms of venereal disease 

 in horses. 



Variola in the horse, while it is identical in principle, general course, 

 complications, and lesions with variola in other animals, is a disease of 

 the horse itself, and is not transmissible in the form of variola to any 

 other animal; nor is the variola of an^' other animal transmissible to 

 the horse. Cattle and men, if inoculated from a case of horsepox, de- 

 velop vaccinia, but vaccinia from the latter animals is not so readily 

 reinoculated into the horse with success. If it does develop, it pro- 

 duces the original disease. 



Etiology. — The direct cause of the horsepox is infection. A large 

 number of predisposing causes favor the development of the disease 

 as in the case of strangles, for this trouble, like almost all contagious 

 diseases, renders the anima^l which has had one attack immune from 

 future ones. The causes are, young age, for then the animal is still 

 susceptible to contract the disease, but old horses which have not been 

 affected are less apt to become infected when exposed than younger 

 ones. The exposure incident to shi])ment through public stables, cars, 

 etc., again acts as a i^redisposing cause as in the other infectious dis- 

 eases. The period of final dentition is a moment of the animal's life 

 which renders it peculiarly susceptible. 



Dupaul states that the infection is transmissible through the atmos- 

 phere for several hundred yards. The more common means of conta- 

 gion is by direct contact or by means of fomites. Feed boxes and 

 bridles previously used by horses affected with variola are probably the 



