West Nile hit North America 1999 and was discovered in PA in 2002, it started killing crows and other birds in the Corvid family as well as horses. I am not sure they even know how long it has been killing grouse but you are correct that the big dip in the grouse population is a combination of death in grouse from the virus and the loss of good grouse habitat which is young regenerating forests. The Ruffed Grouse Society has been working closely with the Pa Game Commission in the planting of trees and shrubs in areas on game lands across the state in areas being managed for grouse. Pa does log on state game lands and other lands for both habitat and income. The double whammy of loss of habitat and the WN virus has been a kick in the teeth, we can do something about the habitat, controlling mosquitoes is a lot harder. Just one more problem caused by importing things from other countries and especially 3rd world countries.