Etiology, Pathogenicity, Natural Infection. 853 



The virus is present in the blood, in the urine and in the 

 feces of the affected, also of the apparently recovered animals. 

 The saliva has no infectious properties (Ostertag). Whether 

 there exists any kind of a relation between infectious anemia 

 and horse pest has not been decided (see p. 286). 



Tenacity. The virus los-es its virulence entirely when heated to 58° C, dry- 

 ing at room temperature does not influence it; thus dry blood serum was found 

 harmless only after seven months (Carre & Vallee). In storing the blood without 

 drying it loses its infectiveness only after three months. The virus resists putre- 

 faction for a long time, even in strongly animoniacal substances (urine, manure). 

 Thus Carre & Vallee found urine of an infected horse, kept in a manure pit, virulent 

 even after 214 months. 



Pathogenicity. The disease may be produced artificially 

 in horses by intravenous or subcutaneous administrations of 

 virulent blood or blood serum, immaterially whether larger 

 quantities (up to 750 cc.) or very small quantities (1 cc.) 

 are injected (Carre and Vallee). The disease of the test 

 animals is indicated by a febrile rise of the temperature, which 

 according to Carre and Vallee always occurs within 5 to 9 

 days; in one of Marek's cases however the incubation lasted 

 for 18 days. The disease in test animals rarely develops with 

 the same characteristics as in animals from which the blood 

 has been procured. To produce a successful infection per os, 

 larger quantities (at least 15 cc.) of virulent blood or urine 

 are" necessary according to Ostertag, and in such cases the 

 incubation also extends over a longer time, 15 to 24 days. The 

 incubation period may however be shortened by the repeated 

 administration of great quantities of virulent material. Donkeys 

 cannot always be infected (Carre & Vallee, Marek), while other 

 domestic animals, also small test animals are entirely resistant 

 (Carre & Vallee, Ostertag, Marek). Man also resists the in- 

 fection. 



The experiments of Ostertag and Marek proved that, after an intestinal as 

 well as subcutaneous or intravenous infection, the disease in test horses not infre- 

 quently runs a chronic course, and aside from periodical rises in temperature, for 

 a long time causes no noticeable disturbances, a condition which deserves notice 

 in transmission tests. 



Natural infection may occur indirectly through the inges- 

 tion of food or drinking water contaminated by urine or with 

 feces of affected animals. As the urine and feces always con- 

 tain the virus, but especially during the febrile attack, and as 

 it is very resistant against outside influences, there is an ample 

 opportunity afforded for indirect infection. The virus is taken 

 up either with the bedding or with the grass in the pasture, 

 or the food may become contaminated by attendants or in 

 other ways, especially in insanitary stables. With the ichor, 

 or more directly with feces or urine, the virus may contaminate 

 the drinking water, for instance by draining from the manure 

 pit or in the pasture. On the other hand a direct transmission 

 does not appear to occur. Carre & Vallee failed in demonstrat- 



