In Animals: There are 4 modes of transmission in pets:
1) Congenital: kittens or puppies may be born with hookworms. Hookworm larvae are tiny enough to migrate through the placental blood supply to the fetal lungs. Soon after birth, the juvenile hookworms are coughed up and swallowed. They then mature in the small intestine; attach to the intestinal wall and begin sucking blood and laying eggs.
2) Transmammary: infection may occur through mother's milk. Hookworm larvae can gain entry into the mammary glands and be passed to the puppies or kittens as they nurse. The larva then mature in the intestine to form blood sucking adults.
3) Ingestion: The dog or cat could swallow a hookworm larvae found in the environment (like on a blade of grass, a toy, water or food dish),
4) Skin Penetration : dogs or cats could lie down on top of hookworm larvae that use proteases to penetrate the animals' skin.
In Humans: Humans are accidental hosts, and are infected by skin penetration.