A gram-negative, bipolar-staining rod, isolated from a snowshoe hare in Alaska, was identified as Pasteurella pestis. This identification was of particular importance since plague is under international quarantine and has never been reported from Alaska. Subsequent work has established that the organism is a strain of P. pseudotuberculosis type I B which possesses an antigenic substance very closely related to the Fraction I antigen of the plague bacterium. The presence of this antigen resulted in the fluorescent-antibody test yielding a false-positive finding, and has raised the question as to the current emphasis in differentiating between these two bacterial species on the basis of the presence or absence of Fraction I. The determination of P. pestis must include other testing procedures, such as the isolation of the organism or the demonstration of its presence in tissues of test animals.
Communicable Disease Center, Public Health Service, U. S. Department of Health, Education, and Welfare, Technology Branch, San Francisco Field Station, San Francisco, California 94118. (Address for reprints.)
Institute of Hygiene and Medical Microbiology, University of Bern, Bern, Switzerland.
U. S. Army Chemical Corps Laboratories, Fort Detrick, Frederick, Maryland.
George Williams Hooper Foundation, University of California, San Francisco, California.