CCWR ACTION ALERT: 2006 West Nile Virus Surveillance: Tree Squirrels

TO: CALIFORNIA MOSQUITO AND VECTOR CONTROL AGENCIES
FROM: KERRY PADGETT, Ph.D., VECTOR-BORNE DISEASE SECTION
SUBJECT: 2006 WEST NILE VIRUS SURVEILLANCE: TREE SQUIRRELS
DATE: January 18, 2006


In 2006, the California Department of Health Services, Vector-Borne Disease Section (DHS) will support tree squirrel testing for West Nile virus (WNV) surveillance throughout California. Between June 2004 and November 2005, 42% (97/ 230) dead tree squirrels tested by RT-PCR were positive for WNV in California, similar to the prevalence in dead birds. Samples from the following tree squirrel species were WNV positive: Fox Squirrel (n = 68), Western Gray Squirrel (n = 23), Eastern Gray Squirrel (n = 3), and 3 unspecified squirrels. Based on these findings it is clear that tree squirrels are susceptible to WNV and, due to their small home range, are excellent surveillance animals in peridomestic settings.

Beginning in 2006, tree squirrel WNV test results will be posted on the State of California WNV website (www.westnile.ca.gov). This site has been updated with educational information on WNV and tree squirrels. With expanded reporting, DHS anticipates additional interest on the part of the public to submit dead tree squirrels. Due to zoonotic disease potential of mammals, the public will NOT be directed to drop off dead squirrels at local mosquito and vector control agencies. It will be the responsibility of agencies to pick up and submit dead mammals. As with dead bird surveillance, participation is at the discretion of the local agency. Those agencies that prefer not to submit tree squirrels should contact Ryan Carney (rcarney@dhs.ca.gov).

The protocol for tree squirrel submission will remain unchanged in 2006 (i.e., squirrels should be dead no longer than 24 hours, no maggots…). The following tree squirrel species will be accepted for testing: Fox Squirrel (Sciurus niger), Western Gray Squirrel (S. griseus), Eastern Gray Squirrel (S. carolinensis), and Douglas’s squirrel (Tamiasciurus douglasii). In addition to tree squirrels, a limited number of lagomorphs (rabbits and hares) will be accepted for WNV testing. Ground squirrels will NOT be accepted – any suspicious die-off of ground squirrels should be referred to county health departments for plague testing. All dead mammals should be handled using gloves, plastic bags, or a shovel and shipped to CAHFS following the same protocol used for dead birds.

Any questions that pertain to tree squirrels and WNV testing can be directed to Colleen Barclay (cbarclay@dhs.ca.gov) at (510) 412-06251 or Ryan Carney (rcarney@dhs.ca.gov) at (510) 412-6254.