Both kittens and adult cats may become infected by swallowing eggs that contain infective roundworm larvae. These eggs may come from the feces of infected cats or from the tissues of paratenic hosts (an accidental host). In a paratenic host, the roundworm eggs do not mature into adults, but are just transported.

How does my indoor cat get roundworms?

Roundworm eggs can be brought indoors on shoes or clothes, and if they're accidentally eaten by your cat, your cat may become infected. Roundworms can also be passed to kittens through their mother's milk, so a young cat might already have worms before they arrive at your home.

How do common house cats get worms?

How Do Cats Get Worms? Cats most commonly contract worms after coming into contact with parasite eggs or infected feces. A cat may walk through an area with eggs or infected feces, and since cats are often such fastidious groomers, they will then ingest the eggs or fecal particles as they clean their fur and feet.