Experimental plague in the California ground squirrel

Area of Science:

• Veterinary Medicine
• Infectious Diseases
• Ecology

Background:

• Plague, caused by Yersinia pestis, remains a significant zoonotic disease.
• Understanding host susceptibility is crucial for disease management and surveillance.
• California ground squirrels are a potential reservoir for plague in endemic regions.

Purpose of the Study:

• To determine the current susceptibility of California ground squirrels to a local Yersinia pestis strain.
• To evaluate the dose-response relationship for infection and mortality.
• To assess the implications for plague transmission in squirrel populations.

Main Methods:

• Experimental inoculation of California ground squirrels (Spermophilus beecheyi) with varying doses of Yersinia pestis.
• Determination of the 50% infectious dose (ID50) and 50% lethal dose (LD50).
• Monitoring of serologic response to the Yersinia pestis fraction 1 antigen and mortality rates.

Main Results:

• The ID50 was determined to be 256 Yersinia pestis, while the LD50 was 6,070 Yersinia pestis.
• A dose-dependent relationship was observed between Yersinia pestis challenge dose, serologic response, and mortality.
• Squirrels surviving high-dose challenges (≥60,700 Y. pestis) consistently showed seroconversion, though antibody titers remained low (≤1:64).

Conclusions:

• California ground squirrels demonstrate significant resistance to Yersinia pestis infection and mortality.
• The observed dose-response dynamics suggest a role for resistant squirrel populations in regulating plague's enzootic and epizootic cycles.
• Further research is needed to fully elucidate the ecological factors influencing plague transmission in these populations.