I’m going to leave the medical part of your question to our vets, but I do have an observation regarding what makes a reputable, ethical breeder.
Unless the person from whom you purchased your puppy titles (as in, they earn titles through showing, obedience trials, etc…not just AKC registration) and fully health tests per the Chihuahua Club of America, they aren’t what I would consider ethical or reputable. Here’s a lot more information: http://www.chihuahuaclubofamerica.org/health-committee-mission/
Read through the links on the right sidebar. And maybe look into an insurance policy to cover potential health issues. Petplan and Truepanion seem to be two of the best…avoid VPI like the plague, they’ll just take your money.
A washcloth with warm soapy water should be used to clean the wound. Some diseases are transmitted by mice and could be problematic please contact your vet.