Worms in Cats: How to Detect, Treat, & Prevent [Vet-Approved]

A photo of a cat sadly looking straight ahead to represent internal worms in cats or parasites in cats

One common concern that pet owners encounter is the presence of worms in cats. These pesky parasites can affect cats of all ages and breeds, and if left untreated, they can lead to various health complications. 

Often, these parasites in cats go unnoticed because not all worms show obvious signs until the infection has already progressed. Furthermore, worms in cats can spread through microscopic eggs and larvae, as well as through ‘intermediate host’ insects. 

In this article, we will talk about the most common worms in cats — along with their associated symptoms, treatment options, and preventive measures. By understanding these, cat parents will be better equipped to protect their beloved feline companions.  

What’s in This Guide? 

What are Worms in Cats?

Worms in cats are internal parasites that can infest their digestive system, heart, or lungs. These parasites in cats can come in various forms but their commonality is that they feed on the cat’s nutrients in some way or another. 

Note: Some types of internal worms in cats can be transmitted to other species, such as dogs and humans.

Worms in cats have different life cycles which influence:

  • where they reside in the cat’s system;
  • how they are spread or transmitted; and 
  • what symptoms they cause. 

In the upcoming sections, we have distilled crucial parasitology information that every cat parent should be aware of. We’ve also marked which parasites in cats are ‘zoonotic’ (can be spread between animals and humans) to help pet parents take necessary precautions.

Most Common Types of Worms or Internal Parasites in Cats

1. Roundworms in Cats

Intestinal | Can be zoonotic | Pathogenic

Where Roundworms in Cats Reside

Unlike some other intestinal parasites in cats, roundworms do not attach to the intestinal walls. Roundworms in cats swim freely and steal the nutrients they need from partially digested food. Roundworms get their name from the tube-like shape of their body. 

After roundworm eggs hatch in the intestines, the larvae migrate to other tissues (lungs, liver, and muscles) before returning to the intestines where they mature into adult worms. 

Roundworm Species That Infect Cats (+ Risk Level for Humans)

Roundworms in cats come mainly from two species: Toxocara cati and Toxascaris leonina. Of the two, T. cati is recognized as zoonotic, meaning the species is capable of infecting humans. However, T. leonina can infect dogs. 

How Roundworms in Cats are Transmitted: 

Roundworms in cats can be spread through the following ways:

  • To newborn kittens: from infected breast milk 
  • To kittens and cats: from infected stool (Kittens and cats can accidentally step on trace amounts of infected stool containing microscopic worm eggs and lick the worm eggs from their paws during grooming.)
  • To kittens and cats: from consuming infected prey (i.e. some species of rodents and birds)
  • To kittens, cats, and humans: from contaminated soil

Symptoms of Roundworms in Cats

So what symptoms are associated with roundworms in cats? Here’s a list of symptoms pet parents can watch out for:

  • Diarrhea
  • Dull hair
  • Weight loss (but with a potbellied appearance)
  • Worms in cat vomit
  • Worms in cat poop (since the roundworms in cats are not anchored to the intestinal walls, they are more likely to show up in cat poop — unlike other species of parasites in cats that are ‘attached’.)
A cat being examined for weight loss, which is one of the symptoms of roundworms in cats

2. Tapeworms in Cats

Intestinal | Zoonotic | Rarely causes serious disease in cats

Where Tapeworms in Cats Reside

Tapeworms in cats typically reside in the small intestines where they attach themselves to the intestinal lining. This is where tapeworms are able to feed off food that’s undergoing digestion.  Unlike some other worms in cats, tapeworms are not known for migrating to other vital organs. This is one of the reasons why tapeworms in cats do not typically produce serious symptoms. 

Tapeworm Species That Infect Cats (+ Risk Level for Humans)

The most common species of tapeworms in cats is known as ‘Dipylidium caninum’, a type of tapeworm that also infests dogs. These parasites in cats can infect humans — albeit rarely, considering how tapeworms in cats and dogs are transmitted. 

How Tapeworms in Cats are Transmitted: 

The most common species of tapeworms in cats, D. Caninum, requires an ‘intermediate host’ to infest and spread: the flea. The life cycle of tapeworms in cats starts when the tapeworm egg is ingested by a flea larva. Once this flea larva matures into an adult flea, it is capable of transmitting tapeworm to certain organisms (e.g. cats, dogs humans).

For transmission to occur, the flea needs to be ingested. For cats and dogs, this can easily happen while grooming, especially if their skin is itchy because of fleas. For humans, however, accidental flea ingestion is very rare, which explains why tapeworm infestation does not, in many cases, transfer to pet parents. 

Symptoms of Tapeworms in Cats

As stated earlier, tapeworms in cats typically do not cause serious symptoms. However, there are still a few clues that pet parents can look for to determine if a cat may have a tapeworm infestation. These include the following:

  • NO worms in cat poop - instead, cats may pass white tapeworm segments called ‘proglottids’, which can move if freshly passed. Proglottids are egg-containing segments that detach from tapeworms but are usually mistaken for maggots or grains of rice.
  • Signs of anal ‘pruritus’ (itching) - cats may exhibit behaviors that help relieve itching in their anal region (i.e. licking, biting, scooting).
  • Weight loss & worms in cat vomit - though rare, this can happen — especially in cases of heavy tapeworm infestation
A cat after licking their anal region, which is indicative of anal pruritus, one of the symptoms of tapeworms in cats

3. Hookworms in Cats

Intestinal | Zoonotic | Pathogenic

Where Hookworms in Cats Reside

Cat hookworms can be located in the intestines. These parasites in cats derive their name from the hook-like structure they use to anchor themselves into the intestinal wall. Hookworms feed on the cat’s blood. 

In cats, some hookworm larvae can migrate to the lungs through the bloodstream. Once there, they are expelled through coughing and subsequently swallowed, returning to the intestines.

Hookworm Species That Infect Cats (+ Risk Level for Humans)

There are two main hookworm species that infest cats:  Ancylostoma tubaeforme and Ancylostoma braziliense. Humans can also be infected with these species of hookworms in cats, meaning these parasites are ‘zoonotic’.

How Hookworms in Cats are Transmitted: 

Cats can get hookworms through the following ways:

  • To kittens and cats: from the stool of infected cats or dogs (Kittens and cats can accidentally step on trace amounts of infected stool containing microscopic worm eggs and lick the worm eggs from their paws during grooming.)
  • To kittens and cats: from ingesting prey animals (e.g. rodents) that can serve as paratenic hosts’ (an optional intermediate host to the parasite).
  • To kittens, cats, and humans: from contaminated soil

Note: Both humans and pets have the potential to acquire hookworms through contaminated soil in two primary manners: ingestion and direct skin contact. Hence, consuming unwashed vegetables puts a person at risk of contracting hookworms. Additionally, walking barefoot (or, in the case of pets, having 'bare paws') on contaminated soil can lead to a hookworm infection, as the tiny larvae of hookworms can penetrate the skin through burrowing.

Symptoms of Hookworms in Cats

So what are the symptoms of hookworms in cats? Look out for the following:

  • Lethargy (lack of energy)
  • Weight loss
  • Pale gums
  • Heavy breathing
  • Bloody or dark stool
  • NO worms in cat poop (unlike some other worms in cats, hookworms are usually attached to the intestinal wall, making it unlikely for them to be found in the cat’s stool. Instead, only microscopic hookworm eggs are passed.)
A cat showing lethargy or lack of energy, which is one of the symptoms of hookworms in cats

4. Heartworms in Cats

Lungs & Heart | Zoonotic - very rare | Pathogenic

Where Heartworms in Cats Reside

Heartworms are one of the most dangerous worms in cats because they occupy delicate vital organs. These worms occupy the lungs, heart, and associated blood vessels as they feed off the host’s blood. 

These worms can grow to around 8 inches in length which makes them a possible cause of obstruction in the organs they occupy. They can also cause inflammation and other complications.

Even a low count of heartworm can be dangerous for cats. As further explained by Sploot’s veterinarian, Dr. Allison Kihn, “When cats get heartworm, they generally have a low worm burden — but a couple of heartworms can be just as detrimental in a cat as a massive infection in dogs.” 

More About Heartworm (+ Risk Level for Humans)

Though heartworm is a species of roundworm, they behave differently from intestinal roundworms which were covered in an earlier section. This is why we’ve dedicated this section just to heartworms. 

The species of heartworm in cats is called ‘Dirofilaria immitis (the same species that affects dogs). Humans can, in very rare cases, also get heartworm, but the parasite cannot come directly from pet dogs and cats. Humans are what’s known as a ‘suboptimal host’, which means that heartworm cannot go through their entire life cycle inside the human body. 

How Heartworm in Cats is Transmitted

The mode of transmission for heartworm is subtle and can happen anywhere. This is what makes this parasite exceptionally dangerous for pets. Heartworm is transmitted (to dogs, cats, and suboptimal hosts like humans) through the bite of an infected mosquito that is carrying the heartworm larva. This means that even indoor pets can be at risk, particularly during the warmer times of the year when mosquitoes are most active. 

Symptoms of Heartworm in Cats 

So how can a cat parent tell if a cat has heartworm? Here are clues to look out for:

  • Weight loss
  • Reduced appetite
  • Lethargy (lack of energy)
  • Shortness of breath
  • Persistent coughing
  • Vomiting
  • Aversion or reluctance to exercise
  • Nose bleeds
  • A swollen abdomen (more common in heavy infestations, this is caused by fluid accumulation from heart failure)

Note: Unfortunately, some cases of heartworm in cats can lead to sudden death. This emphasizes the importance of having regular heartworm preventives for cats. 

A cat ignoring their food, showing reduced appetite, which is one of the symptoms of heartworm in cats

5. Lungworms in Cats

Airways or lungs | Can be zoonotic | Pathogenic

Where Lungworms in Cats Reside

Depending on the species, lungworms in cats can reside either in the linings of respiratory airways (e.g. windpipe, bronchi) OR in the lungs. 

Lungworm Species That Infect Cats (+ Risk Level for Humans)

Of the four species of lungworm that can infect cats, the most notable are ‘Aelurostrongylus abstrusus (which is the most common form) and ‘Eucoleus aerophilus.’ Both of these lungworms can also infect dogs. As for people, A. abstrusus is not a health concern — but E. aerophilus can infect people

Transmission among pets (as well as from pets to pet parents) is NOT observed, due to how lungworm is transmitted. 

How Lungworms in Cats are Transmitted:

Pet cats can get lungworm in different ways, depending on the species of lungworm.

  • A. abstrusus - cats contract this lungworm by ingesting an infected snail or slug OR by ingesting a prey animal (e.g. a lizard, frog, bird, or rodent) that has recently ingested an infected snail or slug 
  • E. aerophilus - cats contract lungworm by accidentally ingesting the eggs or larvae which is usually found in infected soil.

Symptoms of Lungworms in Cats

It is important to get lungworms in cats treated promptly before it causes serious damage to the respiratory system. Watch out for the following symptoms:

  • Poor appetite 
  • Fever
  • Weight loss
  • Coughing
  • Wheezing
  • Sneezing
  • Heavy breathing
A cat sneezing and coughing, which are symptoms of lungworms in cats

Diagnosing Worms in Cats - Can It Be Done at Home?

This guide covers various symptoms and risk factors that pet parents can use to watch out for worms in cats. However, only a licensed veterinarian can conclusively diagnose worms in cats. Diagnosis can involve both the clinical assessment of symptoms AND laboratory testing. 

Veterinarians may recommend that your pet undergo tests like fecal flotation (wherein a fecal sample is inspected under a microscope for worm eggs or larvae) plus/minus a fecal antigen testing (which detects proteins that are released by a parasite). In addition, the Baermann technique can be used by veterinarians, specifically for detecting lungworm larvae. These tests, which make use of fecal samples, are useful for diagnosing intestinal worms and lungworms respectively

Meanwhile, when testing for heartworm in cats, a blood sample (NOT a fecal sample) is used to detect antigens (proteins from female worms) AND antibodies (proteins released by the cat’s immune system) specific to the parasite. Veterinarians may also request chest X-rays to aid in diagnosing heartworm infections in cats. 

Note: Fecal flotation and fecal antigen testing can also detect another microscopic parasite: giardia. Giardia is a microscopic protozoan that causes giardiasis, a diarrheal disease.  

As a final note, even though pet parents cannot diagnose parasites in cats at home, the symptoms of parasitic infections still serve as actionable clues. The next best thing to total prevention is prompt treatment. We recommend cat parents to reach out to a veterinarian upon seeing concerning symptoms. 

Are Worms in Cats Life Threatening?

All of the parasites in cats that are mentioned in this article have the potential to cause serious symptoms. Some have fatal consequences. There are various factors to consider when assessing the danger of worms in cats — such as the cat’s overall health and age, the worm burden, the length of infection, and the species of worms present.

The factor of age and overall health is important because worms in cats can generally be life-threatening for kittens, older cats, and immunocompromised cats. In addition, long-standing infections with a high worm burden tend to show more complications, regardless of the species of worm present. However, some parasites in cats are simply dangerous by virtue of their species alone; for example, heartworm has a high potential to be life-threatening, even for otherwise healthy cats. 

How to Prevent Worms in Cats & Kittens

When approaching worms in cats and kittens, prevention is key. Here are the main preventive measures cat parents can take:

1. Deworm Kittens

Ensuring kittens receive deworming is crucial as they can acquire parasites either before birth or during nursing. In addition, kittens, with their developing immune systems, are more vulnerable to parasites in cats and more likely to exhibit serious symptoms. 

The administration of deworming medication for kittens usually involves oral treatment that follows a prescribed schedule over a number of weeks. To initiate the process of kitten deworming (as well as other kitten preventive care steps), it is advised to contact your veterinarian for guidance.

2. Give Heartworm Preventives to Your Pet

While many medications are used to treat heartworm in dogs, the same isn’t true for cats. There is currently NO approved anti-heartworm medication for treating infected cats. 

Medication can be given to manage the symptoms of a heartworm infection, but not to eliminate adult heartworms. In some cases, cats may require surgery to have adult heartworms removed.

To protect cats from heartworms, pet parents need to use heartworm preventives for cats. Preventives can kill larval-stage heartworms but they cannot kill adult heartworms in cats. Therefore, heartworm preventives for cats need to be given within a scheduled interval. This way, any larval heartworms can be killed while they have not YET reached adulthood.   

Note: Heartworm preventives for cats are administered topically or orally. Consult your veterinarian to get the best heartworm preventives for your cat.

3. Check & Treat External Parasites Promptly

Tapeworms in cats are transmitted through infected fleas. Therefore, it is important to prevent exposure to fleas and to promptly treat flea infestations.

Speaking of flea prevention, we’d also like to remind pet parents that it is crucial to remain vigilant about ticks as well. Ticks have the ability to harbor bacteria, viruses, and unicellular parasites that can spread diseases, especially among humans and dogs. Some notable examples of tick-borne illnesses include Lyme disease and Rocky Mountain Spotted Fever. Cats are less susceptible to tick-borne diseases than dogs but are not wholly immune.

4. Regular Wellness Exams

Wellness exams play a vital role in preventing various illnesses, including parasites in cats. At Sploot, we highly encourage our clients to have their pet cats undergo a yearly wellness exam. Yearly exams can include an annual fecal testing, especially for cats that are at high-risk for parasites (i.e. cats that regularly venture outdoors and socialize).

Promptly identifying worms in cats can lead to early treatment, thereby preventing various complications. However, in some cases, surgical intervention may be required — especially for heartworm, a parasitic infection in cats that does NOT have an FDA-approved drug for treatment.  

Final Thoughts About Worms in Cats

We hope this guide on parasites in cats was helpful! We talked about modes of transmission, symptoms, and prevention tips. If you have further questions about worms in cats, we recommend reaching out to a veterinarian. 

As for pet parents in Denver & Chicago, Sploot Veterinary Care is here to help! We are a primary & urgent care veterinary clinic with multiple convenient locations. If you’re concerned about a possible worm infestation or you’d like to take the next steps towards preventive care for your cat, reach out to our team; you can also book an appointment online or through the Sploot Vets app. We also accept walk-ins during our extended vet clinic hours. 

Till next time, we’re with you every pounce of the way!