Dogs get worms through several common routes involving ingestion or skin contact with parasite eggs, larvae, or intermediate hosts:

• Fecal-oral infection: Dogs ingest worm eggs or larvae from contaminated feces or soil. This is the most frequent way dogs acquire roundworms, hookworms, whipworms, and other intestinal parasites. Eggs shed in infected dog feces contaminate soil and can remain viable for long periods, infecting dogs who sniff, lick, or eat dirt or grass

• Transplacental and transmammary infection: Puppies can be infected before birth through the placenta or after birth through their mother's milk. Roundworms often pass this way in utero, and hookworms can be transmitted through nursing

• Transdermal infection: Hookworm larvae can penetrate the dog's skin when walking on or contacting contaminated soil, entering through paws or belly skin

• Eating infected intermediate hosts: Dogs can get worms by eating infected wild game, small mammals (like rodents), raw meat, or carcasses. Tapeworms often require an intermediate host such as fleas; dogs become infected by ingesting fleas during grooming

• Fleas: Tapeworms are transmitted to dogs primarily through ingestion of infected fleas, which carry tapeworm larvae

• Mosquito bites: Heartworm disease is spread to dogs through mosquito bites, which transmit heartworm larvae

In summary, dogs commonly get worms by ingesting worm eggs or larvae from contaminated feces or soil, through their mother's infection before or after birth, by skin penetration of larvae, by eating infected animals or fleas, and through mosquito vectors for heartworms