I don't have any personal experience of zappers or any of this but I guess it's important you now help his immune system as much as possible and help him detox.
Lots of Vitamin C and vitamin/mineral supplements, probiotics suitable for pets (Primal Defense is a good one).
Does Dr Clark give any advice on how to strengthen the immune system and detox? Maybe a herbal detox?
Maybe look into quickly finding a holistic veterinarian.