Helpful references for traveling with pets can be found on the USDA website at https://www.aphis.usda.gov/aphis/pet-travel/helpful-references.
It says on that site that health certificates must be signed by a USDA-accredited veterinarian, and there is information about how to find one of those at https://www.aphis.usda.gov/aphis/pet-travel/find-a-vet.