Vaccination of Monkeys with Agar-Tissue Cultures of European Rickettsiae

In a previous paper, we reported the successful vaccination of guinea pigs against European typhus, using agar-slant tissue cultures. 1 Since guinea pigs do not give a Weil-Felix reaction, and since they show very little other than a temperature during the course of a typhus infection, it seemed desirable to test our vaccine on animals which more nearly resemble man in their reactions. Three Macacus rhesus monkeys of approximately the same size were selected. One was reserved as a control, the other 2 were vaccinated with formolized vaccine prepared in the following manner: Rickett-siae of classical typhus were grown with minced mouse embryo tissue on agar slants for 7 to 9 days. The tissue was removed from the slants and ground in a small mortar, after which 3 cc of 0.2% formolized saline were added for each slant. (For human use, we recommend a light centrifugation at this point.) After being cultured for sterility, the vaccine was allowed to stand in the ice box for a week before use to insure the death of the rickettsiae. The vaccine was administered subcutaneously at 5-day intervals. Monkey No. 1 was given a total of 4 cc, the equivalent of 1 1/3 agar slant cultures, the amount used in the guinea pig experiments previously reported. Two weeks after the last dose, the Weil-Felix reaction was negative, the agglutination for European Rickettsiae 1/20++, 1/40++, 1/80++, 1/160+. Monkey No. 2 was given a total of 6 cc of vaccine, representing 2 agar slant cultures, in doses of 1, 1, 2, and 2 cc. Three weeks after the last dose this monkey's serum showed an agglutination with B. proteus O × 19, of 1/20 and a Rickettsia agglutination of 1/20+++, 1/40+++, 1/80++, 1/160++, 1/320+.