HORSEPOX. 525 



This disease was described by the early Roman agricultural writers 

 and by the veterinarians of the eighteenth century. It received its 

 first important notice from the great Jenner, who confounded it with 

 grease in horses, since animals with this disease are very apt to have 

 the eruption of variola appear on the fetlocks. 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. Horsepox 

 is also 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 any other animal 

 transmissible to the horse. Cattle and men, if inoculated from a case 

 of horsepox, develop vaccinia, but vaccinia from the latter animals 

 is not so readily reinoculated into the horse with success. If it does 

 develop, it produces the original disease. 



Causes. — The direct cause of horsepox is infection. A large num- 

 ber of predisposing causes favor the development of the disease, as 

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

 diseases, renders the animal which has had one attack immune. The 

 chief predisposing cause is young age. Old horses which have not 

 been affected are less apt to become infected when exposed than 

 younger ones. The exposure incident to shipment, through public 

 stables, cars, etc., acts as a predisposing cause, as in the other infec- 

 tious diseases. The period of final dentition is a time of the animal's 

 life which renders it peculiarly susceptible. 



Dupaul states that the infection is transmissible through the at- 

 mosphere for several hundred yards. The more common means of 

 contagion is by direct contact or by means of fomites. Feed boxes 

 and bridles previously used by horses affected with variola are proba- 

 bly the most frequent carriers of the virus, and we find the lesions in 

 the majority of cases developed in the neighborhood of the lips and 

 nostrils. Coition is a frequent cause. A stallion suffering from this 

 disease may be the cause of a considerable epizootic, as he transmits 

 it to a number of brood mares and they in turn return to the farms 

 where they are surrounded by young animals to whom they convey 

 the contagion. The saddle and croup straps are frequent agents of 

 infection. The presence of a wound greatly favors the inoculation of 

 the disease, which is also sometimes carried by surgical instruments 

 or sponges. Trasbot recites a case in which a set of hobbles, which 

 had been used on an animal suffering from variola, were used on a 

 horse for a quittor operation and transmitted the disease, which 

 developed on the edges of the woimd. 



