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


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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7 thoughts on “Ask a Vet: Why Did My Kitten Vomit a Roundworm?”

  1. Jennifer Boban Leon

    I adopted a stray kitten and I think it would be hardly 2-3 months old. Today it puked almost 4-5 times right after eating food. The second time it puked we saw a live worm. We tried giving it some water but won’t drink. It looks very weak but shows a lot of energy even after vomiting and cried for food. We stopped giving it food after the fourth time it puked. Could you please advise what to do?

  2. I found an abandoned kitten during a thunderstorm in a parking lot. We estimated his age to be 3 weeks. I’ve had cats for years and I’m a 50 year old person. I brought it home and I fed it with a bottle until it was a little over 2 lb. he’s now eating cat food and water on his own. I also gave him his first deworm treatment. He hasn’t acted sick all day, he’s been playing and very happy and his normal kitten self. But a few hours later he vomited up something that I couldn’t identify. The only thing I can think is that it is dead worms? Would that look like chewed up ramen noodles? And should I allow him to eat his kitten food after this? Even after he vomited up the pile of ramen noodle looking things, he’s bouncing around like he feels good. He’s been gaining weight well, although he is a little skinny because he was half-starved when I found him. He’s been growing so fast it’s been really hard for him to keep up with his eating and calorie needs. I’m sure the worms weren’t helping either. I’m hoping he’ll plump up a little bit after this worming.

  3. Hi, my cat recently gave birth to her second litter of kitten,s and l believe they all survived,so there were 4. The first litter of 4 1 of the babies died and another one was sick, but l was able to save it. With the second litter all 4 seemed to be doing real good, then all of a sudden they got sick and the biggest one died first and we thought he was ok. The other 3 got real weak and didn,t even want to breast feed with their mama and then another one died and the last 2 are still alive, but 1 of them don,t want to feed off mom and won,t eat anything or even drink anything,so l have to force it to drink kitten,s milk that l bought. It just lays around all the time, but l also noticed that it threw up worm,s a couple times and even pooped w worm,s, so l can only think that either mom,s milk infected them and wondered about the fleas, as one of the dead one,s was so bad,that when l bathed it, alot of blood filled the water from the fleas being removed. I can,t afford to take them to a vet, but was woundering what do l do now that the last kitten isn,t eating or drin anything and l haven,t even noticed it go to the bathroom anymore. What do you think?

    1. Hi Teresa — Please contact a vet or rescue group to explain this situation.
      Here’s advice on how to handle vet bills and find affordable vet care but please do not delay getting these kittens professional medical attention:

  4. my five-month-old cat threw up alive worms this afternoon. He was dewormed one-month ago. My boyfriend says that the throwing up incident is caused maybe by the deworming activity last month. I am very worried about my cat. He is a grey strifed coated cat and half a persian cat. By the way, I would like to ask if my cat can sleep on the couch or on the bed because i am afraid his worms can be transmitted to humans – to us. Please help me. What should I do.
    Thank you so much for hearing me.

  5. My 7-month old stray (approximate age determined by veterinarian) was dewormed at a Veterinary Hospital, Tapeworms they said. Soon after I noticed worms again. I took Casanova (my kitten) back! When I questioned why he had to come back so soon concerning worms I was told he was initially treated for a different kind of worms. These were now Round Worms. This morning my baby threw up Round Worms!!
    Doesn’t one dewormer take care of both kinds? And how is it possible he has Round Worms again so soon! He is strictly an indoor Cat! I have three other cats – also indoor cats only. Never had worm issues before so I find this quite alarming! And, of course, I am taking Casanova in to the vet today but can’t help but wonder if they are doing something wrong.
    This is why I am seeking your advice.
    Thank you so very much for your time.

    1. Hi Audrey,
      I know it seems confusing and frustrating. There are different medications for different worms . Even though the common factor is the name, the actual DNA of these parasites are different. It is possible that your kitty had more than one type also . Round worms will not hurt your kitty as long as you get them treated. I do highly suggest asking your vet for extra medicine for the other 2 kitties as even though you may not have seen any. Clean the litter box with fresh litter weekly and use 1 part bleach to 5 parts water to clean it and rinse it. Do this outside because bleach fumes are more harmful than the tapeworms.

      I wish you the best and a long future with your little kids :)

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