On the Specificity of Epidemic and Murine Typhus.
The specificity of epidemic and murine typhus has been shown by active immunization of mice with killed rickettsial suspensions and subsequent challenge with heterologous and homologoustoxic substance. During the preparation of this manuscript, Fitzpatrick published findings showing that 3 of 8 mice immunized with murine typhus vaccine were protected against 3 MLD of epidemic toxic substance administered intravenously and that 8 of 16 mice immunized with epidemic vaccine were protected against < 1 MLD of murine typhus rickettsiae administered intraperitoneally (2). These results suggested to Fitzpatrick that the toxic factor in the two strains is identical. Although there are antigens common to both strains, our findings do not support the suggestion that the two toxic substances are identical.
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