Roundworm infection can occur when a mother cat infected with the parasite nurses her kittens. The stress of pregnancy results in the mother cat becoming re-infested by roundworms. As the mother's immune system weakens, the larvae -- infective stage of a worm -- that were being held dormant in her muscle tissues can become active again or new larvae can be ingested. These are then passed through the milk to the nursing kittens.
In addition, adult cats that ingest infective eggs -- usually by cleaning their paws after stepping on the eggs -- will get roundworms. Outdoor cats that hunt may develop a roundworm infection if they eat prey that hosts the parasite. If infective roundworm eggs are picked up from the soil onto the paws, a cat can become infected by ingesting them while grooming.
