Abstract

Plague (Yersinia pestis) causes periodic and dramatic die-offs of prairie dogs. Plague may thus adversely affect black-footed ferret (Mustela nigripes) reintroduction efforts both by reducing ferret prey populations and by killing ferrets, a species also susceptible to plague. The development of a standard model for plaque pathogenesis using a well-characterized virulent Y. pestis strain is essential for vaccine testing. The Siberian polecat (M. eversmanii) is the closest living relative of the black-footed ferret and is indigenous to the old world, where plague originated and was endemic. To determine if this species would offer a suitable model for plague pathogenesis and prevention in the black-footed ferret, we assessed plague susceptibility and pathogenesis in pure defined-strain Siberian polecats (M. eversmanii dauricus). We exposed 33 individually housed polecats to 103 (n=7), 107 (n=7), or 1010 (n=7) Y. pestis organisms by SQ injection, or by feeding an intact, freshly plague-killed mouse (n=12). An additional group of seven unexposed animals given otherwise identical care and housing served as controls. Plague exposure led to an 88% mortality overall in polecats (71% mortality in the 103 group, 100% mortality in the 107 and 1010 groups, and 83% mortality in the mouse-fed group). None of the controls died or showed signs of illness during the 21-day trial period. Within the challenged group, mean survival time post-challenge ranged from 3.6–12.6 days. Animals that received the lowest parenteral dose survived significantly longer than those receiving higher parenteral doses. The survival time of polecats ingesting plague-killed mice was intermediate between that of low and that of high parenteral dose groups. Age, gender, pedigree, and baseline weight were not significantly related to survival status. Within the challenged group, mean survival time was lower in animals presenting with significant weight loss by day 3, lethargy, and low fecal output; onset of lethargy and other signs was also inversely related to risk of dying and/or plague dose. The results of this study confirm that the Siberian polecat is susceptible to plague and suggest that this species will offer an appropriate surrogate for black-footed ferrets in future plaque studies and related vaccine trials.