Reaction of the Rabbit to Vaccine Virus

Little information is available regarding the clinical reaction of the rabbit to cutaneous inoculation of dermo-vaccine virus except as regards the local reaction at the site of injection. Furthermore, factors which presumably might affect the response as, for example, age, have not generally been considered. Our interest in the matter arose from the results obtained in the vaccination of the rabbits of a large breeding colony. The experiments are still in progress but enough has been learned to show that the clinical reaction of the rabbit to vaccination is extremely variable and that these variations are associated with a number of factors which concern the host.

Approximately 1800 rabbits were vaccinated in December, 1933, and January, 1934, with culture dermo-vaccine virus obtained through the kindness of Dr. T. M. Rivers. The injections were made intracutaneously with dilutions ranging from 1:50 to 1:40,000. Previous tests had shown that the virus was active in a titre of 1:100,000 to 1:1,000,000 injected intradermally. Certain outstanding results of the experiments may be briefly summarized as follows.

A typical local reaction developed in the adult non-immune stock of both sexes but it was much more severe in bucks than in does, and more pronounced in resting than in pregnant and nursing does. Generalized manifestations consisting in particular of a cutaneous maculo-papular eruption in areas remote from the injection site, as for example, the ears, were not infrequent. A lymph adenitis was also observed and an orchitis in male animals developed in many instances. There were a few cases of pronounced illness and prostration but only 3 fatalities.

The results were quite different in the younger stock, all of which were presumably susceptible. In the first place, a local reaction did not develop in a large proportion of these rabbits and the incidence of negative results was inversely proportional to age.