478 SHEEP POX 
toward the end of the 16th century. Its infectiousness was estab- 
lished by Bourgelait in 1763 at which time it was very widely dis- 
tributed in Europe. Its etiology has been studied, especially by 
Chaveau in 1866 and Borrée in 1902. 
Geographical distribution. Sheep pox is quite widely distributed 
in Europe, Asia and Africa. It is reported to have appeared for the 
first time in Great Britain in 1847, having been brought there from 
Denmark. The outbreak lasted for four years and caused heavy 
losses. It is stated by Hutyra and Marek to have been eradicated 
from Northern Europe but that it still exists in France and in the 
countries lying south and east where it is of considerable economic 
importance. 
Etiology. The cause is believed to be a virus which is able to pass 
through the Berkefeld filter but not through the Chamberland F. 
As in other variolas, it is contained within the vesicles, pustules and 
scabs. Nocard found it was restricted to these and that the blood 
was not virulent. Ostertag and others have found that the disease 
was transmissible by blood inoculation. According to Ostertag 
sheep are sometimes capable of transmitting the infection for three 
months after recovery. He believed the virus was retained in the 
wool. It is destroyed promptly by direct sunlight, high temperature 
and putrefaction. 
Duclert found that the virus was attenuated when kept in glycerin. 
A mixture of equal parts of glycerin and lymph from the vesicles 
became non-virulent in 12 days when kept at a temperature of 25° C. 
Its virulence is attenuated at a temperature of 48° C. 
Natural infection is supposed to take place through the respiratory 
tract, the virus passing into the circulation and carried by this means 
to the skin and mucous membrane. According to Nocard the disease 
can be invariably produced by injecting the virus into the trachea. 
Metastatic abscesses in the joints and meninges have been reported. 
Shedding of the hoofs has been observed. Suppuration of the 
lymphatic glands, subcutaneous abscesses, ulceration of the mucous 
membranes, septic pneumonia, ulceration and gangrene of the nasal 
bone and cartilage have been reported. 
The period of incubation is reported to be from 2 to 20 days. Oster- 
tag found it to be from 8 to 12 days. 
Symptoms. The first symptoms are a rise of temperature, catarrh, 
dullness, loss of appetite with acceleration of the pulse and respiration. 
