St. Louis Missouri, Michigan, or Oklahoma? No need to say here; but though to share that in St. Louis MO West Nile Virus was confirmed in mosquitoes. This virus presents with lethargic symptoms, being especially common to find in areas that WNV is present in young squirrels yet to get their full pelage.
Were any of these symptoms noted in this article present before the one squirrel expired?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1939863/