Pets can be infected with worms in a variety of ways:

1. Oral Ingestion: Pets are infected in this fashion when they ingest a parasite egg or larvae from a contaminated environment. These eggs then either mature into an adult worm in the intestinal tract or go into a state of dormancy.
2. Transcutaneous: In this case, pets are infected when parasite larvae penetrate the skin of a host and migrate through the bloodstream.
3. Transmammary: Puppies and kittens often become infected with parasites when they nurse. This is because dormant larvae living in the muscles of mature pets become activated hormonally during pregnancy, migrating through the mammary system to the nursing puppies or kittens.
4. Transplacental: Puppies can become infected with intestinal parasites in the womb when the mother transfers dormant larvae into her unborn young.
5. By Ingesting Fleas: One kind of tapeworm is transmitted when a pet ingests a flea hosting the embryo. These embryos then mature in the pet during the digestive process.
6. By Ingesting Other Hosts: Rodents, ruminants, birds and rabbits can serve as secondary hosts for many worms. Pets become infected when they consume these secondary hosts.