Awww - poor Chewy, I am sorry but at least you know what it is now. I have no experience but found this information.
Giardia canis in Dogs
It does appear to be contagious and there is even speculation that it can be transmitted to humans tho it has not been proven. Hopefully someone with actual experience or insight will be here soon to help you.
Good luck and I hope that Chewy is better soon.