DISEASES OF THE HORSE. 547 



METHOD OF INFECTION. 



All evidence now available .seems to indicate that surra is strictl}' a 

 wound disease, nanieh^ that the parasite ma}^ enter the bod}'^ only 

 through a wound of some kind. Apparently by far the most common 

 method is through wounds produced by biting flies, whose mouth 

 parts are moist with the infected blood of some animal bitten by the 

 same flies immediately previous to biting the healthy animal. Crows 

 may also transmit the infection by pecking at sores on a diseased 

 anim.al, soiling their beaks with blood, and transferring this infected 

 bloo4 to a healthy animal. Likewise, if a scratch is made on a horse 

 and then infected blood is rubbed on the scratch, the horse will 

 become diseased. If, in experiment, infected blood is fed to a healthy 

 animal, the latter may contract surra in case it has an abraded or 

 wounded spot in its mouth; but if no part of the lining of the alimen- 

 tary canal is wounded, infection does not take place. Thus dogs and 

 cats may contract the disease b}^ wounding the lining of the mouth (as 

 with splinters of bone) while feeding on the carcasses of surra sub- 

 jects. All available evidence indicates that under normal conditions 

 of pregnancy the disease is not transmitted from mother to fetus. 



There is a popular view that surra may be contracted by drinking 

 stagnant water and hy eating grass and other vegetation grown upon 

 land subject to inundation, but there is no good experimental evidence 

 to support this view. Probably the correct interpretation of the facts 

 cited in support of this theory is that biting flies are numerous around 

 bodies of stagnant water and in inundated pastures, hence that a great 

 number of possible transmitters of the disease are present in these 

 places. 



SYMPTOMS. " 



Symiytoins of the disease as ohserved lohen contracted naturally. — The 

 invasion of this disease is usuall}^ marked b}" symptoms of a trivial 

 character; the skin feels hot, and there may be more or less fever; 

 there is also slight loss of appetite, and the animal appears dull and 

 stumbles during action; early a symptom sometimes appears which 

 ma}' be the first intimation received of the animal's indisposition, and 

 which, as a guide to diagnosis, is of great importance; it is the pres- 

 ence of a general or localized urticarial eruption. If the blood be 

 examined microscopicall}', it may be found to present a normal appear- 

 ance; but in the majority of cases a few small, rapidly moving organ- 

 isms will be observed, giving to the blood, as it passes among the 

 corpuscles, a peculiar vibrating movement, which if once observed 

 will not easily be forgotten. If the parasite has not Ijeen discovered 

 in the blood for some days, the symptoms mentioned above may be 



«iyiis summary of symptoms is based upon work by Lingard, as summarized in 

 the Emergency Report. 



