Make sure to keep him inside for a while. It is ideal to go tto a vet to get prescribed antibiotics and pain medication, because even if they don't show it, they are in pain, and antibiotics can realy help.
Wash him until they are gone.
Google it, and this is what I found
"Chicken and turkey parvovirus infections occur worldwide and primarily affect growing birds. The primary signs are related to production and include poor weight gain, poor feed conversion, and failure to thrive. Diarrhea and increased mortality can also occur."
If you think the heat is causing this, DO NOT blow-dry him. I do not think 50° could cause something like this, though. Go with your gut instinct, because chickens love blowdriers, and a happy chicken usualy feels better faster.