Experimental infection of ground squirrels (Citellus pygmaeus Pallas) with Yersinia pestis during hibernation

Objectives: In this study, we investigated the capability remain latent infection of Yersinia pestis in ground squirrels (Citellus pygmaeus Pallas) after their challenge with Y. pestis over the hibernation period. Methods: Ground squirrels were challenged with Y. pestis by either subcutaneous injection (n = 106 animals) or by infected fleabite (n = 33 rodents). The development of plague in hibernating rodents was monitored daily for the signs of illness; if the animal died, the spleen, liver, lung, lymph nodes, bone brain, kidney and blood were taken for bacteriological and histopathologic examinations. Results: In 35.8% (38 of 106) of the ground squirrels the plague has been developed after the challenge with Y. pestis via the s.c. injection within eight months, i.e. winter, spring and summer the periods of the observation. Overall, in 48.5% (16 of 33) of the animals the plague was developed during three months after the challenge with infected fleabite. The infection with Y. pestis was confirmed by bacteriologically and histopathological changes, e.g. pneumonia and necrosis in tissues of the ground squirrels. Conclusions: The results support the hypothesis that Y. pestis can remain latent in winter-sleeping ground squirrels during their hibernation and this phenomenon plays an important role in the epizootics of rodents after reawakening in the spring. (C) 2006 The British Infection Society. Published by Elsevier Ltd. All rights reserved.