try to gently clean it and have some one hold him for you , but you should look very closely at the skin on the swolen area and see if you can find a small puncture mark, that be a spidder bite . here we get spiders that like to over winter in our dog houses , im not sure what kind they are but a few years ago that hapened to one of my dogs. large swollen area/chills/fever/tenderness. if you see a small hole that could be what happend. we just kept it very clean and aplied topical antibiotics to it and it went away