West Nile virus infection in tree squirrels (Rodentia: Sciuridae) in California, 2004-2005

Kerry A. Padgett, William K. Reisen, Nicole Kahl-Purcell, Ying Fang, Barbara Cahoon-Young, Ryan Carney, Nancy Anderson, Lynda Zucca, Leslie Woods, Stan Husted, Vicki L. Kramer

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


West Nile virus (WNV) transmission generally involves a mosquito vector and an avian reservoir host, with mammals as incidental hosts. Although most mammalian WNV infections cause low or no morbidity or mortality, tree squirrels are susceptible to WNV-associated neurologic disease with infection prevalence comparable to that in dead birds. Positive species included fox squirrel (Sciurus niger), western gray squirrel (S. griseus), and eastern gray squirrel (S. carolinensis). Kidney tissue (dissected and swabbed), and oropharyngeal (oral) swab samples from tree squirrels submitted by California vector control and rehabilitation agencies were tested by reverse transcription-polymerase chain reaction; cycle threshold values were similar for all three samples, ranging from 21.9 to 26.5. Kidney tissue was more sensitive than oral swabs for detecting WNV in squirrels. Three of 36 live neurologic tree squirrels had viremia approximately 5 log10 plaque-forming units/mL or greater, similar to WNV-infected birds. Tree squirrels are useful in WNV surveillance and provide localized evidence of WNV transmission to mammals.

Original languageEnglish (US)
Pages (from-to)810-813
Number of pages4
JournalAmerican Journal of Tropical Medicine and Hygiene
Issue number5
StatePublished - May 2007

ASJC Scopus subject areas

  • Parasitology
  • Infectious Diseases


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