Three ways canine herpes is transmitted:
Direct Contact
Transmission occurs through direct contact between the infected and uninfected dog. The herpes virus cannot live outside its host for long. Transfer of this disease usually occurs through direct contact with the infected host or fresh secretion.
Puppies and Mothers
Herpes virus mainly affects puppies, causing death of one or all of the liter. Puppies are only in danger if the mother has become infected during the pregnancy. If the mother was infected previously, she will have produced enough antibodies against the virus. Subsequent pregnancies should not be affected.
The virus can infect the puppies while they are still within the uterus. They may also be exposed to the virus from vaginal secretions during birth. Nasal secretions by the mother may infect the puppies when they inhale while breathing. Puppies may easily spread the virus from one to another; however, if one is infected it doesn't mean the other puppies are as well.
Orally
Another way for dogs to become infected is by eating infected materials.