Acquired Resistance to Tuberculosis Induced in Red Mice (Clethrionomys G. Glareolus Schreb.) by Vaccination With Living BCG

Abstract

In order to find a method for evaluation of the acquired resistance induced by a BCG vaccine, using red mice as experimental animals, a study was carried out previously to examine the effect of various doses of BCG on a challenge with a relatively small dose of bovine tubercle bacilli ( 5 ) . Doses from 10-1 to 10-5 mg of BCG caused prolongation of the survival time of the animals after challenge as compared to non-vaccinated animals. The interval between vaccination and challenge was seven weeks.The aim of the present work was to determine the dosage range for challenge which can be used to demonstrate acquired resistance in BCG vaccinated red mice. Both the dose of vaccine and the challenge dose were varied within wide limits. Groups of red mice were vaccinated with doses of BCG ranging from 1-2 units to 1.2 X 10O units and subsequently challenged with doscs of tubercle bacilli ranging from 30 to 30 x lo6. E X P E R I M E N T A LFour groups of red mice, each containing 100 animals, were vaccinated with 0.2 ml suspension containing 10-7, 10.0. 10-5, 10-3 or 10-1 mg of living BCG. Each dose was injected subcutancously into 20 animals from each group. After a vaccination period of three months, the four groups and non-vaccinated control groups, were challenged intravenously with virulent bovine tubercle bacilli. The challenge dose was 0.2 ml of dilutions 100, 10-2, 10-4 and 10-6 of tubercle bacilli grown in Dubos' fluid medium with Tween and exposed to ultrasonics. The animals were observed until death occurred spontaneously and the survival time in days after challenge was used as indication of the acquired resistance. In order to control the ability of the mice to survive, the experiment included also a group of 20 animals which were neither vaccinated with BCG nor challenged with tubercle bacilli.This work was carried out with the aid of a grant from " P . Carl Petersens Fond". 383