I just bought 3 new chickens that are a year old. One has this big spot of missing feathers around its vent and the skin looks irritated. I sprayed the Vitrycin stuff on it just now but my main concern is that maybe its a disease that can spread to my other chickens? I isolated the 3 birds for 3 days and they all look fine except that one part on the chickens vent. See the picture. Can it be like that from being pecked? Is it a mite or bug? Please help me solve this and figure it out.