PATHOGENESIS 



It is not the purpose here to deal with variations in 

 susceptibilities or methods of spread of disease or any other factors 

 which presuppose pathogenesis, as these will be dealt with in the next 

 section. This section will serve as an introduction to the section 

 that follows. 



Besides being pathogenic to members of the Salmonidae and other 

 fish in nature, B. salmonicida has been shown experimentally to be 

 infective, by various routes, to a number of other fish and cold-blooded 

 vertebrates. ViTilliamson (1928) showed that infection could be set up 

 in frogs, minnows, and goldfish ( Carassius auratus ) . Intraperitoneal 

 injection vn.th a large inoculum of B. salmonicida was necessary to kill 

 frogs, which suggests that it is unlikely that they would be infected 

 in natiore. She also succeeded in infecting a blenny by intraperitoneal 

 injection of l/lO of an agar slope of B. salmonicida . The organism of 

 furunculosis cannot establish itself in the tissues of warm-blooded 

 animals (Marsh 1902, Williamson 1928). Although susceptible by injection, 

 eels do not readily contract the disease, as attempts to infect them by 

 feeding contaminated food or contact with diseased fish have been 

 unsuccessful (Furunculosis Committee 1933). 



Results of e25)erim8nt clearly show that healthy ova from infected 

 parents are not invaded by the organism and that the organism is not 

 transmitted from parent to progeny through either ova or sperm 

 (Furunculosis Committee 1935). 



It is concluded by the Furunculosis Committee (1935) that the 

 bacterium may invade a new host from water ty the gills, alimentary 

 tract, or in some cases a surface injury, though it proved impossible 

 to state definitely the common natural route. 



DETERMINDIG FACTORS 



Susceptibility of Various Fish to the Disease in Nature 



The Salmonidae 



The disease in natui^e is limited to fish living in fresh water 

 and it has been recorded mainly among members of the family Salmonidae 

 (Furunculosis Committee 1930). As has been shown experimentally, other 

 fish and cold-blooded animals can also be infected (see above). 



Vari ation Among Species an d. I ndividual s 



Table 10 svunmarizes the comparative susceptibilities of various 

 members of the Salmonida e as suggested and found by a number of workers, 

 7dth the least susceptible shown at the bottom of the table. Table 10 

 shows that there is general agreement amongst various workers that 

 rainbovj- trout ( Salmo gairdnerii ) are least susceptible. 



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