280 VETERINARY HYGIENE 



the way for the streptococcus of strangles, which is in part at least 

 responsible for the lesions and for such sequelae as pneumonia or 

 pleurisy which occasionally follow an attack of influenza. Schiitz 

 considered influenza to be due to a diplococcus, which by other 

 observers (Lignieres, &c.) was considered to be at least closely 

 related to the streptococcus of strangles. Inasmuch, however, 

 as it has been shown that the disease can be transmitted experi- 

 mentally to healthy horses by means of blood which has been passed 

 through a bacterial filter, it seems likely that the cause is an ultra- 

 visible one. 



Though influenza is a widespread disease a larger proportion 

 of outbreaks is seen in cities, and especially in such places as horse 

 repositories, dealers' stables, &c. 



Outbreaks are usually of an enzootic nature, and once intro- 

 duced into a stable the disease spreads very rapidly. Isolated cases 

 do, however, occur. The disease has no predilection for young 

 horses except so far that such when brought in from the country 

 undergo a sudden and complete change of life which would in itself 

 render them more receptive to pathogenic organisms. The disease is 

 spread through the agency of the secretions and excretions, and 

 these are said to be especially infectious during the early stages 

 and at the height of the attack. Infection may occur by ingestion 

 of contaminated food, drinking water, &c., though the possibility 

 that it may occur via the respiratory organs cannot be excluded. 

 Infection may thus be direct as from horse to horse or by any of the 

 indirect means described under strangles such as by feeding utensils, 

 broken fodder, grooming tools, water-troughs, and stable attendants. 

 It is also spread by contaminated horse boxes' on railways and by 

 ships. An animal which is convalescent has also to be looked upon 

 as dangerous. A fact conclusively established by clinical and other 

 evidence is that apparently healthy stallions, though not dangerous 

 in the usual sense of the term, are at times capable of transmitting 

 the disease by coitus. They may thus act as " carriers " of the infec- 

 tion for months. Instances of this method of transmission have 

 been noted by Pottie,* Caulton Reeks, j &c. In some of these 

 cases the semen was found to be virulent on inoculation even after 

 it had been passed through a bacterial filter. Mares infected in 

 this way may transmit the disease to other equines by contact. 



The period of incubation is from 3 to 7 days. Most cases 

 recover quickly, but sequelae may supervene and the mortality may 

 reach 15 per cent. (Dieckerhoff). Whether one attack confers any 



* Pottie, Journ. Comp. Path., 1888, Vol. I. 

 t Caulton Reeks, Journ. Comp. Path., 1901, Vol. XIV. 



