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Ask a Vet: Why Did My Kitten Vomit a Roundworm?

Roundworms are extremely common in kittens, and they can even infect humans. Here are signs that you should visit your vet.

Dr. Eric Barchas  |  Aug 18th 2015

I recently received the following question from a reader on my professional website.

Hi, I just read your article on roundworms. I have an 8-week-old kitten who pooped a worm two days ago. I gave him dewormer and today he vomited up a dead worm. He is eating and drinking regularly but this worries me. He has lost some weight. He was given to me by a friend, and I can’t take him to the vet for another three weeks because of financial reasons. The dewormer I gave him is Pro-sense Round Worm Liquid de-wormer. The instructions say treat once and then again in 14 days. Can he be treated sooner?

Thank you,

Roundworms are extremely common in kittens. In fact, their prevalence may well approach 100 percent in kittens (I’m going to go out on a limb here) such as Allynda’s, who were not the result of purposeful breeding.

Adult roundworms resemble spaghetti noodles. They live in the intestines of cats and kittens, and they produce eggs that pass through the feces. Once in the environment the eggs undergo a process called embryonation, in which they become infective to cats and to other species.


Roundworm by Shutterstock

Cats can be exposed to roundworms by consuming an infective roundworm egg (for instance, by walking through a litter area and then grooming the feet). However, other means of exposure also occur. The roundworm eggs might be consumed by birds, rodents, or earthworms (which in turn might be eaten by a bird or rodent); these hosts might disperse the eggs. A cat might become infected by consuming one of these hosts.

How then, you might ask, are roundworms so common in young kittens? Kittens might not ever leave the house, and they consume milk, not prey.

The answer lies in something called transmammary transmission. Roundworm larvae can pass through a mother’s milk and infect the kittens. Transmammary transmission can be prevented by aggressive deworming of the mother, but let’s face it: The sort of cat who gets pregnant (without purposeful breeding) is most likely to be feral or to be owned by the sort of person who is not going to aggressively deworm her.


Cat and kitten by Shutterstock

Cats, birds, rodents, and earthworms are not the only potential hosts for roundworms. Human beings, especially children, can become infected when they are exposed to the infective eggs. When that happens, serious illness can occur. Roundworm larvae can migrate through vital organs, the eye, or even the brain, wreaking havoc as they do so.

The good news is that it generally is safe for people to live with cats. Plenty of kids are exposed to kittens without going blind from roundworm migration. However, it is extremely important for all cats and kittens to be dewormed.

The Companion Animal Parasite Council (CAPC), a group of experts in veterinary parasitology, has issued guidelines for deworming of kittens. CAPC recommends deworming all kittens every two weeks, beginning at two weeks of age and concluding when the kitten is old enough to begin regular broad spectrum heartworm and intestinal worm prevention.

Allynda, the dewormer you used contains piperazine as its active ingredient. Piperazine is an old-school dewormer that has a lower safety margin and efficacy than many other products.


Kitten at the vet by Shutterstock

However, with that said, there is a chance that the dewormer worked. Kittens with heavy worm burdens often vomit worms as the parasites die. In such instances, it also is common for a large number of dead worms to pass into the feces.

Even if the dewormer did work, it is likely that some worms survived. And Allynda mentioned something that always raises a red flag in my mind: Her kitten is losing weight.

Healthy kittens should gain weight continuously. An 8-week-old kitten never should lose weight. Severe worm burdens can cause weight loss. However, other more serious problems (including very dangerous infectious diseases such as panleukopenia) also can cause kittens to lose weight.

What’s more, by the time Allynda states that she can get the kitten to the vet he will be 11 weeks old. Kittens should receive their first vaccine (which helps protect against panleukopenia) between six and eight weeks of age. Eleven weeks is dangerously late.

Allynda, your kitten should receive a better dewormer, and he needs to be vaccinated. His weight loss needs to be evaluated by a veterinarian. I’ll bet he also needs a flea preventative. You need to find the resources to get to the vet immediately.


Kitten in hand by Shutterstock

For the record, I have found that usually it is less expensive in the long run to do things the right way. I have seen people try to save money by using over-the-counter dewormers, only to have to spend hundreds or thousands of dollars treating a toxic reaction. I have seen the same thing happen with cheap flea preventatives. I once treated a cat for a urinary obstruction to the tune of a couple of thousand dollars; the obstruction occurred two days after the owner got tired of paying extra for a urinary diet and switched to a cheaper commercial food.

I do not recommend putzing around with home remedies and over-the-counter products. Allynda, your kitten will be better off and you’ll save money in the long run if you take him to the vet to have him treated properly.

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