Infectious Diseases of Animals. 23T 



Sheep-Pox. 



On the first appearance of this disease in England its true nature was not 

 immediately recognised, although Professor tSimonds, who inspected the 

 diseased sheep at Datchet in 1847, remarked a considerable resemblance 

 between the eruption which he observed on the skins of the diseased animals 

 and that of small-pox as it occurs in man. The matter was considered of sO' 

 much im]X)rtance that an investigation was immediately imdertaken bjr 

 Professor Simonds, Mr. Ceely, INIr. Erasmus Wilson, and Mr. Marson. After 

 considerable inquiry and numerous experiments the following conclusions- 

 were arrived at. 



Sheep-pox is so far allied to small-pox in man as to deserve the title of 

 ovine small-pox. The affection is communicated by inoculation or association, 

 from the diseased to healthy sheep. Experiments which were made to test 

 the communicability of sheep-pox to other farm stock, including horses, cattle, 

 and pigs, gave negative results, as did also inoculation of the human subject. 

 An attack of sheep-pox gives the animal protection against subsequent attacks 

 of the disease, but vaccination is found to have no preservative influence. In 

 fact the vaccine vesicle was not perfectly developed in the sheep in any one 

 instance. 



When sheep-pox is allowed to run its course without interference it passes 

 through a definite number of stages, each of which occupies a certain period. 

 The time of incubation varies from 7 to 14 days, and is followed by the febrile 

 stage of invasion, and this by the development of hard red pimples, which are 

 called papulaa, and which appear from the fourteenth to the sixteenth day 

 after infection. Vesication takes place from the seventeenth to the nineteenth 

 day. Pustules are develojjed from the twentieth to the twenty-second day, 

 and from the twenty-second to the twenty-eighth day the surface of the 

 pustule becomes covered with a brown scab. During the latter part of the 

 period of incubation and the period of invasion considerable fever is present, 

 which is indicated as usual by a rise of the internal temperature. The con- 

 stitutional symptoms which are apparent vary according to the stage of the 

 disease, but they generally 'resemble those which are present in ordinary 

 febrile catarrh. There is discharge from the nostrils, quick breathing, height- 

 ened colour of the mucous membranes, discharge of tears from the eyes, loss of 

 appetite, cessation of rumination, general dulness of aspect, and a tendency, 

 which is always observed among sick animals, to avoid association with others. 

 When the disease assumes a malignant form the discharges become extremely 

 fetid, diarrhoea occurs, and sometimes extensive ulceration of the surface of 

 the skin. These cases usually terminate fatally. 



As in the small-pox of man the virulence of the disease varies considerably 

 in different seasons without any sensible cause. Sheen- pox, when it first 

 appeared in this country, was remarkable for its gi'eat fatalitj'-, the deaths 

 sometimes amoimting to 75 per cent. The outbreak which occuiTed in Che- 

 shire some years afterwards was attended with comparatively insignificant 

 mortality, the deaths sometimes not amounting to five per cent, of the animals- 

 attacked. Sheep-pox is not indigenous to this country. In 1847 the malady 

 was introduced for the first time in this generation along with 56 Merino 

 sheep which were purchased in Smithfield Market on the 20th July, and 

 taken to Datchet near Windsor, The disease shortly appeared among the 

 Merinos, and quickly extended to the Downs with which they had been 

 placed. From this centre of infection sheep-piox rapidly spread until it ex- 

 tended over a considerable part of the country, and its ravages did not cease 

 imtil 1850. From this time England remained free from the disease imtil 

 ] 862, in the summer of which year it appeared at Allington near Devizes. 

 In this case the origin of the outbreak was never satisfactorily ascertained, 

 but it was presumed that the disease had been brought to the district with. 



