SURRA. 549 



METHOD OF INFECTION. 



All evidence nov\' available seems to indicate that surra is strictly a 

 wound disease, namely, that the parasite may enter the body 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 

 animal, soiling their beaks with blood, and transferring this infected 

 blood 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 be- 

 come 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 the mouth ; but if no part of the lining of the 

 alimentary canal is wounded, infection does not take place. Thus 

 dogs and cats may contract the disease by wounding the lining of the 

 mouth (as with splinters of bone) while feeding on the carcasses of 

 surra subjects. 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 by 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." 



Sym.pto7ns of the disease as observed when contracted naturally. — 

 The invasion of this disease is usually marked by 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 may be the first intimation received of the animal's indisposi- 

 tion, and which, as a guide to diagnosis, is of great importance; it 

 is the presence of a general or localized urticarial eruption. If the 

 blood be examined microscopically, it may be found to present a 

 normal appearance; but in the majority of cases a few small, rapidly 

 moving organisms will be observed, giving to the blood, as it passes 

 among the corpuscles, a peculiar vibrating movement, which if once 



o This summary of symptoms is based upon work by Lingard, as summarized in 



tbe Emergency Report. (See footnote on page 548.) 



