Protection of Rabbits Against Naturally Acquired Infectious Myxomatosis by Previous Infection with Fibroma Virus

Abstract

It is generally agreed that the viruses of rabbit fibroma and rabbit myxoma are closely related immunologically and that infection with the benign fibroma virus usually protects rabbits against fatal infection with the myxoma virus. This suggested that the fibroma virus might make a satisfactory immunizing agent for practical use in the control of infectious myxomatosis. The possibility was tested by McKenney and Shillinger with discouraging results, and they concluded that the infection of rabbits with fibroma virus did not constitute a satisfactory or practical means of immunizing against infectious myxomatosis. However, careful consideration of the experiments of McKenney and Shillinger suggests that their difficulties lay more in the maintenance of a potent infective fibroma virus for use in their experiments than in an actual failure of fibroma virus to enhance the resistance of rabbits to myxomatosis. Partly because of McKenney and Shillinger's adverse report on the practicability of using fibroma virus prophylactically and partly to determine whether fibroma-recovered rabbits would prove as resistant when exposed to cases of infectious myxomatosis as they had when inoculated with myxoma virus, the experiment to be reported in this paper was conducted. The testicles from a rabbit inoculated intratesticularly 7 days earlier with strain A fibroma virus were removed aseptically and stored for one month in 50% glycerol in the refrigerator. (The period of storage in glycerol is not important providing it does not exceed 2 months.) At the end of this time they were washed in 3 changes of physiological saline, ground with sterile sand and suspended in physiological saline to make a 5% suspension. After the suspension had stood for 10 minutes in a tall glass graduate, the supernatant fluid was decanted for use as fibroma virus.