Experimental Rabies in White Mice. Studies on Passive Immunization I. ∗

Abstract

The subject of passive immunization against rabies has received relatively little attention, even though Fermi, 1 Pfeiler 2 and others have reported striking experimental demonstrations of the efficacy of anti-rabic serums. In the current report, which summarizes 12 protection tests performed in the past 2 years, the protective properties of such serums have been studied using white mice as experimental animals.

A fixed virus strain, obtained through the courtesy of the Cutter Laboratories, was passed through rabbits and preserved at ice-box temperature, either fresh or in 50% glycerine, for periods which did not exceed 2 weeks. Details of preparation varied, but in effect the virus was ground to an initial dilution of 1/20 in normal saline and centrifuged 10 minutes at 2200 R.P.M. The supernatant fluid was then filtered through “Whatman No. 1′ paper and final dilutions of from 1/100 to 1/800 were made. The virus was injected intracerebrally, at first in amounts proportional to the body weights of the mice (0.005 cc./gm. or 0.001 cc./gm.), later in a constant dose of 0.02 cc.

The serums were prepared by hyperimmunizing rabbits and goats with either 1/10 fresh fixed virus or 1/20 fixed virus preserved with 1/2% phenol. Serums were developed which would neutralize equal volumes of 1/200 fixed virus prepared as above to a final titer of 1/256, when the mixtures were incubated at 37° C. for 2 hours and tested by intracerebral mouse injection. Corresponding normal serums showed no in vitro neutralizing properties. The serums were filtered and inactivated before use.

In the experiments reported the serums were injected intraperitoneally, the first dose being given at intervals ranging from 48 hours to 1 hour before the administration of virus. Doses for each serum injection varied from .05 cc./gm. body weight to .15 cc./gm. Serum was usually given only once, but at times as many as 2 subsequent injections were made, the maximum total of serum given to any mouse being .45 cc./gm. in a period of 5 days.