SWINE FEVER '843 



SECTION XL THE VIRUS OF SWINE FEVER OR HOG-CHOLERA. 



The role which a filter-passing virus is believed to play, according to recent 

 research, in the aetiology of hog cholera has already been adverted to when 

 discussing the bacillus known as Bacillus aertrycke (p. 438). [The conclusion 

 is that Hog-cholera or swine fever is due to a filtrable virus present in the 

 blood of the sick animals and that the hog cholera bacillus (bacillus cholera; 

 suis of Salmon and Theobald Smith) is a secondary infection, which is com- 

 monly present, and which may increase the mortality among infected animals. 



[These facts established first by Dorset and M'Bryde in America have been fully 

 confirmed by MTadyean and Stockman in England, by Uhlenhuth in Germany 

 and by many other observers in countries where swine fever is prevalent. 



[The virus of swine fever will pass through a Chamberland F porcelain 

 bougie : if the blood of a sick animal be diluted ten times it will, after filtra- 

 tion through this bougie, on inoculation in suitable dose into a young pig 

 (10-20 c.c.) give rise to a typical attack of swine fever ; and healthy pigs 

 kept in contact with an infected animal will contract the disease (Stockman). 



[Pigs are the only susceptible animals and after recovery from the disease 

 are immune to further infection. This natural immunity after a natural 

 attack of the disease is an important fact in establishing that the filtrable 

 virus and not the hog cholera bacillus is the cause of the disease. Animals 

 immunized against this bacillus are not immune to swine fever. 



[The virus is present in the blood and in all the internal organs of animals suffer- 

 ing from swine fever. It is also found in the urine, secretions from the eyes and 

 nose and in the pustular eruption on the skin (Uhlenhuth). The excreta do not 

 appear to be infective or to be more precise, are not an important source of 

 infection. Some animals appear to retain the virus for some time after the acute 

 symptoms have subsided. 



[Healthy animals can be infected through the mouth, skin or the mucous mem- 

 branes. The disease can also be transmitted by inhalation. 



[The virus is highly resistant to external influences. It can be preserved 

 in animal tissues or fluids for many months either at room temperature 

 or in the ice chest. Desiccation appears to have no effect upon the virulence 

 of infected material, nor does heating at 58 C. for 2 hours : but heating at 

 72 C. for 1 hour destroys the virus. The virus is more resistant to the 

 action of antiformin than the hog-cholera bacillus. 



[Certain cell inclusions are found in smear preparations from the conjunctivae of 

 almost every animal suffering from swine fever. These are similar to the cell inclu- 

 sions (Chlamydozoa) described by Prowazek and Halberstadter in trachoma which 

 they were inclined to regard as the cause of this disease. No evidence has yet been 

 adduced in favour of the parasitic nature of these cell inclusions (cf. Negri bodies 

 in Rabies). 



Artificial immunization. [Starting from the well established fact that pigs 

 which have recovered from swine fever are immune to the disease attempts 

 have been made to induce an artificial immunity by inoculating susceptible 

 animals with the serum of hyper-immunized animals. 



[Pigs which have recovered from an attack of the naturally-acquired 

 disease are hyper-immunized by inoculating them sub-cutaneously, intra- 

 venously or intra-abdominally with the filtered serum or defibrinated blood 

 of infected animals. 



[The serum is prophylactic rather than curative, and therefore if it is to 

 be utilized to the greatest advantage in an outbreak it should be used at 

 the earliest possible moment after the appearance of the disease. A dose 

 of about 20 c.c. should be inoculated sub-cutaneously as a prophylactic 

 measure. 



