title: Experimental plague in the California ground squirrel.
abstract: In experiments to determine the current susceptibility to plague, it was demonstrated that 256 Yersinia pestis (a local strain of high virulence) were required to produce a 50% infectious dose (ID50) in California ground squirrels (Spermophilus beecheyi) that had been collected in southeastern Monterey County, California; 6,070 Y. pestis were required to produce a 50% lethal dose (LD50). (The LD50 was about 24 times the ID50.) The frequency of serologic response to the specific fraction 1 antigen of Y. pestis and mortality were dose-related. Approximately half of the squirrels inoculated with six to 6,070 Y. pestis survived without seroconversion, whereas antibody to specific fraction 1 antigen was always observed in squirrels that survived challenges of greater than or equal to 60,700 Y. pestis. However, titers never exceeded 1:64. The implications of these data for enzootic and epizootic transmission of plague in resistant squirrel populations are examined.
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000032:analysis; D004197:Disease Reservoirs / Q000662:veterinary; D007113:Immunity, Innate; D010930:Plague / Q000276:immunology* / Q000635:transmission; D012377:Rodentia / Q000276:immunology*; D012589:Sciuridae / Q000276:immunology*; D015010:Yersinia pestis / Q000276:immunology
chemical_list: D000907:Antibodies, Bacterial