STUDIES ON THE ETIOLOGY OF RABBIT POX III. TESTS OF THE RELATION OF RABBIT POX VIRUS TO OTHER VIRUSES BY CROSSED INOCULATION AND EXPOSURE EXPERIMENTS

Experiments are reported in which it was shown that rabbits which had recovered from experimental or spontaneous rabbit pox were refractory to inoculation of pox virus injected by various routes, and in addition did not develop clinical manifestations of the disease under conditions of exposure to florid cases of pox. It was found that pox recovered rabbits were susceptible to inoculation with the virus of virus III disease of rabbits and that virus III recovered rabbits could be successfully inoculated with pox virus. Furthermore, virus III recovered rabbits developed pox when subjected to room exposure in the same manner as did normal rabbits. It thus appears that there is no specific relationship between the two viruses. Rabbits which had recovered from experimental or spontaneous pox were found to be just as susceptible to inoculation with the virus of infectious myxoma of rabbits as were normal rabbits, a result which demonstrates that there is no specific relationship between these viruses. Rabbits which had recovered from experimental or spontaneous pox were refractory to inoculation with culture dermovaccine virus, but vaccine recovered rabbits were not completely refractory to inoculation with pox virus. Under conditions of exposure to clinical cases of pox, adult vaccine immune rabbits did not develop clinical manifestations of pox, but young, recently weaned vaccinated rabbits did contract mild but definite clinical pox. Experimental pox recovered rabbits were partially refractory to inoculation with neurovaccine virus and neurovaccine recovered rabbits were partially refractory to inoculation with pox virus. The refractory condition of the pox immune rabbits appeared to be more pronounced than that of the neurovaccine immunes. The cutaneous lesions which developed from the intradermal injection of pox, neurovaccine, and culture vaccine viruses showed definite differences with respect to the rate and persistence of active growth, amount of edema, hemorrhage, and necrosis, and the degree of tissue destructiveness. These features were most pronounced in the lesions of pox virus and were least marked in the lesions of culture vaccine virus. The differences were particularly apparent in normal rabbits, but they were also present in the lesions which developed in immune animals. It was found that the calf was susceptible to inoculation with pox virus applied to a scarified skin area. There were many similarities in the appearance and course of the pox lesions to those resulting from culture vaccine virus, the New York Board of Health vaccine, and neurovaccine virus similarly inoculated. But the pox lesions were most numerous, much the largest and most destructive, and by far the most persistent while next in order were those of the Board of Health dermovaccine. The results of these various experiments showed that a close relationship obtains between pox virus, on the one hand, and vaccine virus and neurovaccine virus, on the other, but it cannot be said that pox virus is identical in all respects with either one of these viruses. The findings indicated that the relationship between pox and neurovaccine viruses is closer than that between pox and culture vaccine viruses. Upon the basis of the results observed in culture (dermo) vaccine immune rabbits inoculated with or exposed to pox, it appeared that vaccination with vaccine virus offered a method of protection against rabbit pox.