Protective Action of Concentrated Antityphus Serum (Murine Type) Against European Typhus Virus

Abstract

Two of the writers 1 have described a method of producing concentrated suspensions of Rickettsiae from peritoneal washings of X-ray radiated rats infected with typhus virus of the murine (Mexican-American) type. Such vaccines have since been used for human vaccination and for the production of antityphus serum by horse immunization. The reactions in the horse, the Weil-Felix reactions and the prophylactic and experimental therapeutic action of the immune horse sera have been elsewhere described. 2 Therapeutic test in man, which is giving encouraging results in Mexico, was justified by preliminary experiments in guinea pigs. In these experiments, moderate doses of the serum appeared to confer complete protection against the murine virus upon guinea pigs infected after, together with, or even 3 or 4 days before the administration of the serum. In the case of similar protection experiments in which the classical European virus was employed, 3 protection was not absolute, but sufficiently definite to encourage further efforts. Our observations of the close antigenic overlapping of the 2 principal varieties of human typhus Rickettsiae led us to believe that our difficulties, in regard to protecting against the European “humanized” virus, might be quantitative and could be overcome by increased potency of the antityphus horse serum. The present note reports work by which we believe the difficulty has been overcome.

With the cooperation of the Massachusetts Antitoxin and Vaccine Laboratory, where our horse serum is produced, a method of concentration has ken developed which has furnished a product which in moderate dosage protects guinea pigs against powerful injections of the European virus.

The method of concentration is, briefly, as follows: Typhus horse serum, produced as previously described (Weil-Felix test complete usually at ablaut 1-320), is centrifuged in a Sharples centrifuge.