Zoological gardens offer excellent habitat for squirrels and other rodents by providing food and water resources, shelter, and some protection from natural predators. Moreover, zoos are generally a safe haven from rodent poisons because of the risk posed to zoo animals. However, ground squirrels are often considered pests at zoos due to their disease transmission potential and destructive burrowing behaviors.1 In 2006, three non-human primates at Wildlife Safari were infected with tularemia; two died and one survived with treatment. In the summer of 2008, a disease surveillance and population control pilot program was initiated in the 600-acre drive-through zoo. This involved serosurveillance of California ground squirrels (Spermophilus beecheyi) plus population control measures using either vasectomy/hysterectomy or euthanasia. Our goals were to 1) determine the seroprevalence of tularemia, plague, leptospirosis, and toxoplasmosis and 2) compare the success of two methods of population control—sterilization and euthanasia.
Squirrels were seronegative for Yersinia pestis (n=45, cELISA) and Toxoplasma gondii (n=20, agglutination test); prevalence was low (2%) for Francisella tularensis (n=45, MAT test) and moderate (57%) for Leptospira spp. (n=42, MAT test). This study provides a baseline for further serosurveillance, which could be useful in predicting years in which tularemia may be a risk to zoo animals. Vaccination of high-risk animals against leptospirosis is judicious. Preliminary population control data suggest euthanasia will not result in long-term squirrel control. The efficacy of sterilization following a breeding season has yet to be determined.
We would like to thank Oregon State University, Department of Biomedical Sciences for funding, and Oregon Department of Fish and Wildlife for the use of squirrel traps. Also, thank you to all of the veterinary students and Wildlife Safari staff who provided assistance with the project.
1. Spelman, L.H. 1999. Vermin control. In: Fowler, M.E. and R.E. Miller (eds.). Zoo and Wild Animal Medicine: Current Therapy 4. WB Saunders; Philadelphia, Pennsylvania. 114–120.