524 BUREAU OF ANIMAL INDUSTRY. 



This disease was described b}^ the earl}^ Roman agricultural writers 

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

 portant 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 small- 

 pox, which led to the discovery of vaccination. Horsepox is also 

 frequently mistaken for the exanthemata attendin!,»- 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 anj^ 

 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 pro- 

 duces 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 stjibles, cars, 

 etc., acts as a predisposing cause, as in the other infectious diseases. 

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

 renders it peculiarl}' susceptible. 



Dupaul states that the infection is transmissible through the atmos- 

 phere for several hundred j-ards. The more common means of con- 

 tagion is by direct contact or b}" means of fomites. Feed boxes and 

 bridles previously used by horses affected with variola are probabl}' 

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

 majority of cases developed in the neighborhood of the lips Jind nostrils. 

 Coition is a frequent cause. A stallion suffering from this disease ma}^ 

 be the cause of a considerable epizootic, as he transmits it to a number 

 of brood m.ares and the}" in turn return to the farms where t\\e,j 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 spongt^. 

 Trasbot recites a case in which a set of hol)bles, 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 wound. 



