Can heartworm larvae in an infected mother dog spread to the puppies through her bloodstream?
answer Yes, however these infections are of little consequence to the puppies. The stage of heartworm circulating in the mother’s blood are the microfilaria, the first larval stage of heartworms. The microfilaria can not develop into adult heartworms until they first pass through the mosquito. Only through the mosquito bite can a pet become infected with heartworms. Any microfilaria transmitted to the unborn puppy will be eliminated when the puppy is placed on heartworm prevention.