Fox Encephalitis and Canine Distemper.

A virus disease of dogs has been clearly defined by Laidlaw and Dunkin 1 as “canine distemper”. A virus disease of foxes has also been defined by Green and co-workers, 2 , 3 which, previously described as fox distemper, has been called “epizootic fox encephalitis”. Through the kindness of Laidlaw and Dunkin, the viruses identified in the 2 investigations have been exchanged for comparative study.

While various methods of comparison have shown the 2 viruses to be distinct, the susceptibility of the ferret to the one and not to the other proves conclusively that epizootic fox encephalitis and the canine distemper described by Laidlaw and Dunkin are distinct entities. For the experiments here reported, young foxes and ferrets raised in careful quarantine were available. The fox encephalitis virus was a brain and spinal cord emulsion prepared from the pooled brains of 20 foxes dying of the experimental infection. The dosage used for both foxes and ferrets was 1 cc. of a 5% emulsion. This dosage was, then, enormously greater, in proportion to body weight, for the ferrets than for the foxes. Five fox pups 5 months old and 5 ferrets 2 1/2 months old were injected subcutaneously with the same preparation of virus. The foxes showed a typical experimental infection of encephalitis, one dying on the fourth day, one on the fifth day, and 2 on the sixth. One fox showed grave symptoms on the fourth and fifth days but recovered. The 5 ferrets, during the same period, showed no signs of infection. Their condition was carefully noted from the eighth to the fifteenth day after injection, this being the period during which ferrets die from the virus of Laidlaw and Dunkin. At no time were any symptoms of disease noted.