280 Hog Cholera. 



Immunization. Practical results can be only hoped for from 

 a method of iiiiiiiiuiization which will afford effective protection 

 against prinmry infection with the hlterable cholera virus. After 

 the demonstration of the latest facts regarding the etiology of 

 the disease by establishing the virulence of the filtered tissue 

 fluids of affected animals, experiments were undertaken to work 

 out a suitable metliod of immunization, and they have already 

 led to valuable results. 



Purely practical obf^ervations showed years ago that animals recovering from 

 hog cholera were usually immune for their entire lives. This fact has been utilized 

 by Hungarian hog feeders, as they prefer to feed animals from herds in which 

 the disease has already caused ^onie losses. As a matter of fact they pay consid- 

 erably higher prices for such animals. 



The idea of using serum from hogs which recovered from cholera for immu- 

 nizing purposes, was first utilized by Preisz (1897). He obtained serum from a 

 hog which had been convalescent for three weeks after a severe attack of cholera, 

 and in which the autopsy revealed marked lesions of cholera in the intestines and 

 mesenteric lymph glands. The serum was injected into 30 pigs from 3 to 4 months 

 old, each animal being injected with 10 ce. of such serum. These 30 animals were 

 later placed in a stable with 30 healthy pigs, and with several affected hogs. In 

 the course of one month, 18 of the inoculated animals became sick, and 9 of them 

 died, while all of the control animals succumbed (the last one after 4 months). 



As a result of these findings immunization with blood serum from slaughtered 

 or recovered animals has been used extensively in Hungary. The results however 

 failed to come up to expectations, which probably was due to the fact that the 

 material was not always taken from recovered animals which had passed through a 

 severe form of the affection. 



After the presence of the causative factor of the disease had 

 been recognized in the filterable virus, the attempt was imme- 

 diately made to hyperimmunize hogs artificially, according to 

 the method of immunization used against rinderpest, and 

 thereby prepare a suitable serum for passive immunizati^on, and 

 by the simultaneous use of virulent blood to produce, if possible, 

 an active immunity. These expectations have been fulfilled, 

 insofar as satisfactory methods of immunization have been de- 

 veloped which are practical for both purposes. 



1. Immunization with Immune Serum. (Passive Immuniza- 

 tion.) According to the experiments of Dorset, McBryde & 

 Niles, Uhlenhuth, X^dander, Hiibener & Bolitz, Ostertag and 

 Stadie, as well as Hutyra & Wetzl, hogs which acquired an 

 immunity from a natural or artificial infection of hog cholera, 

 wdien injected by a single large dose, or by several small doses" 

 of virulent blood, produce a serum which protects susceptible 

 hogs for at least three weeks against artificial, as well as against 

 natural infection. This immunity is also effective during the 

 first six days of the incubation period (Ilutyra & Wetzl). The 

 results in practice proved satisfactory, as with the aid of this 

 method it is possible to considerably reduce the losses in herds 

 which have been affected only for a short time, and in many 

 cases to check the outbreak abruptly. Besides this, in animals 

 which are in the stage of incubation, or which have only been 

 affected for a few days, the serum possesses a curative action. 

 It was found further that in infected herds the animals which 



