found this article...
West Nile Virus and Tree Squirrels
In some regions of California, tree squirrels have tested positive for West Nile virus.
Tree squirrels with West Nile virus may display neurological signs such as uncoordinated movement, paralysis, shaking, or circling. It should not be assumed that every squirrel with neurological signs has West Nile virus, as there are other factors that cause these symptoms. Do not handle a sick squirrel as they are wild animals and may bite. Tree squirrels are classified as game mammals by the California Fish and Game Code and can be controlled only as provided by hunting regulations.
Maybe this is a possibility, the paralysis...lots of skeeters out here now,