Don't worry my chihuahua has this. It's not curable but treatable, it's not contagious from one dog to the other only from mom to offspring. The vet should give you a dip and shampoo to treat this. It works. I didn't know my dog had this because she's a rare blue chihuahua and they are prone to hairloss but she did. It's just faded. It's CRUCIAL that you spay or neuter the hormone change will cause him or her to have episodes. Let me know how if goes
wish you all the best.