Ask a Vet: So My Cat Threw Up a Baseball-Sized Mass of Worms. Um, Help?


Hi Dr. Barchas,

Two Siamese cats showed up at our yard and I managed to eventually get them to come in. One of them threw up a baseball-sized ball of worms – roundworms and tapeworms – all wound up together. She seems to have a vision problem, could that be from the worm infestation? I gave her a Drontal pill in hopes that it would help although I don’t know her weight. Should I give her another Drontal in a month? Thanks much.


A baseball-sized ball of worms is not only disgusting. It is an awful lot of worms. But, given the background of the cats you have adopted (or have they adopted you?), intestinal worm infestation is not surprising. In fact, for cats with the background you describe intestinal worm infestation is inevitable.

You have listed two types of worms, and you seem to know the difference between them. For those readers who aren’t completly caught up on feline parasitology, here is a brief explanation of each worm type. Tapeworms are segmented intestinal parasites that involve intermediate hosts (that means that tapeworms must develop for a time in an animal other than a cat). The most common feline tapeworm uses fleas as the intermediate host. Homeless cats are likely to be flea-infested, and they swallow tapeworm-carrying fleas when they groom themselves. This can lead to significant tapeworm infestation. Less common feline tapeworms involve prey animals as intermediate hosts. Cats with good homes don’t consume many prey animals, but a previously homeless cat has the potential to be infested with out-of-the-ordinary tapeworms.

Tapeworms rob cats of nutrients, and they can rarely cause gastrointestinal inflammation or issues with motility of the gut. Fortunately, tapeworms do not frequently cause serious illness in cats. However, segments of tapeworms can crawl out of cats’ anuses and onto bedding where they can cause significant contamination.

Roundworms also are ubiquitous. Huge numbers of cats, especially homeless cats, catch roundworms from their mothers when they nurse (roundworm larvae can pass through the mammary glands and into milk). Roundworms also may be contracted by eating infected intermediate host, or by ingesting eggs directly from the environment.

Roundworms have significant potential to cause serious illness in humans. People who are exposed to infective roundworm eggs (which happens most often to children in gardens and sand boxes) can suffer significant medical harm. Roundworm larvae can migrate through various tissues, causing damage as they travel. Visceral larva migrans involves roundworm larva migrating through internal organs such as the liver or heart, leading to inflammation and potentially failure of the affected organ(s). Cerebral larva migrans involves roundworm (most commonly from raccoons, but also potentially from cats or dogs) larva migrating through the brain. Cerebral larva migrans can lead to seizures, paralysis, and death. Finally, ocular larva migrans involves roundworm larva traveling through the eye. This can lead to vision deficits.

In other words, roundworms can lead to vision problems. However, this is much more likely to happen in a human than in a cat, where abberrant larval migration is much less common.

Ginny, there are plenty of potential reasons other than worm infestation that might explain your cat’s vision problems. These might include hereditary issues, eye problems (such as glaucoma) unrelated to worms, and systemic body problems like high blood pressure.

Although the worms aren’t necessarily linked to the vision problems, they still need to be eliminated. Drontal is an effective treatment for both tapeworms and roundworms, but it must be dosed properly and should be used (and by law in the United States only can be used) under the supervision of a veterinarian. Your cats also need veterinary examinations (with special emphasis on the eyes), stool tests (to confirm that parasites other than roundworms and tapeworms aren’t present), tests for leukemia and FIV, and probably vaccines.

As Hamlet might have said, get thee to a veterinarian.

Got a question about cats? Ask Dr. Barchas in the comments section below.

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