VIRULENCE OF TULAREMIA AS RELATED TO ANIMAL AND ARTHROPOD HOSTS1

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Abstract
In exptl. transmissions of tularemia directly from wild-life forms, tularemia transferred from naturally infected grouse to guinea pigs produced prolonged infections averaging 15 days before death. Guinea pigs injd. from infected rabbits died after an av.. duration of 6 days. A similar difference was evident in the disease produced by injn. of ticks from grouse and from rabbits. As the grouse strains of tularemia were passed through guinea pigs, the length of the infection decreased until it was identical with that of rabbit-strain infections. It therefore appears that Pasteurella tularensis naturally infecting grouse has lowered virulence for guinea pigs and that this virulence is increased by serial passage. The virulence of tularemia strains isolated from ticks found on rabbits and grouse appears to be detd. by the animal or bird host from which the arthropods obtained their infection.