A Failure to Find Virus III Infection in Rabbit Breeding Stocks

Abstract

Rivers and Tillett 1 , 2 and Miller, Andrewes and Swift 3 , 4 had no difficulty in recovering Virus III by serial testicular passage in presumably normal laboratory-stock rabbits. The disease occurred in the 3d, 4th, 5th, or 6th passage in over 30% of trials. Fifteen to 20% of stock rabbits were either refractory to infection or contained neutralizing antibodies in their serum. No other record of the isolation of Virus III has been found. Recently, for use in some contemplated studies on this disease, it seemed desirable to obtain a new strain of the virus from spontaneous cases. The following report deals with that attempt.

Two groups of 8 rabbits of varying age were selected. The initial inoculum consisted of an emulsion of a spontaneous mammary rabbit-tumor. This was injected in 0.4 cc amounts in each testis of the first rabbit of each series. The rabbits were killed at intervals of 4 days, their testes excised under aseptic conditions, ground with sand and sterile salt solution, and injected in 0.5 to 1 cc amounts into the testes of the next of each series. In no instance was there any clinical or histological evidence of Virus III infection. It seemed probable that failure was due to the absence of the virus in the animals used in this laboratory, all of which come from the breeding stock developed by Dr. Wade H. Brown of The Rockefeller Institute. This supposition was confirmed by the fact that of a group of 90 from the same source which were inoculated at various times with Virus III, no rabbit failed to develop either clinical or histological evidence of infection.

Therefore a search was instituted for an infected stock. This was done by testing the sera of sample rabbits for neutralizing antibodies by their ability to inhibit growth of Virus III in tissue-cultures. The occurrence of the typical Virus II inclusion-bodies in the nuclei of the proliferating cells was used as a criterion for the presence of virus.