Worms in Cats


Parasitic worms are a common problem in cats, and typically cause nonspecific symptoms such as coughing, diarrhea, loss of appetite, and vomiting.  Worms can be transferred to felines through contact with an infected animal’s feces or contaminated soil, eating another parasitic host such as a bird or a rodent, or through a mosquito or flea bite.  The most common worms found in cats include roundworm, hookworm, tapeworm, lungworm, eyeworm, and heartworm.  The parasites live off of the nutrients that they derive from the cat’s body, and will begin to multiply rapidly once inside.  Some cats will display visible symptoms once infected, and others will not show any signs at all.  For this reason, it is very important to have your veterinarian evaluate your cat annually to check for an infestation (Petfeed).

Worms in Cats - Universal signs (1)

Most parasitic worms are species-specific, however some worms found in cats can also be transferred to humans. Contact with contaminated soil or feces could potentially lead to accidental infestation, resulting in eye, lung, heart, and neurological problems. It is important to learn about the different types of parasitic worms in cats, and how to protect yourself and your family in the event that your pet becomes ill.


There are many ways that a cat can become infested with a parasitic worm, such as by eating or stepping in soil or feces that contains worms or worm larvae.  Worms often live in small animals including birds, reptiles, and rodents, so consuming any of these animals could also transfer a parasite to a cat.  Mosquitoes, fleas, and ticks can carry worms as well, so a bite from one of these insects could also pass along a worm.  Kittens are at a high risk of contracting a parasite from drinking their mother’s contaminated milk while nursing.

Identifying which parasite your cat has can be tricky, as many worms are microscopic and cannot be seen with the naked eye.  Below you will find detailed information on behaviors your cat may be exhibiting, as well as characteristics about each worm.  Remember, your veterinarian is the best resource if you think that your pet might have a parasite, and routine check-ups are vital to keeping your cat in good health.

When should my cat get tested?

Heartworm: Cats should be tested before being placed on heartworm preventatives.  Since there is no approved treatment medication for felines, the only way to keep cats worm free is to administer year-round prevention.

Intestinal Worms: According to the Companion Animal Parasite Council (CAPC), all animals should receive a preventive physical exam at least every 6 to 12 months.  Fecal examinations by centrifugation should be conducted at least four times during an animal’s first year of life, and then at least two times per year thereafter.  Learn more about fecal centrifugation and parasite testing on our Cat Treatment and Prevention page.

Roundworm for both cats and dogs

Roundworms are the most common intestinal parasite of cats, and affect around 25-75% of cats, with higher rates in kittens (Cornell University, 2018).  Roundworm larvae hatch in a cat’s gastrointestinal tract and move through the muscles, liver, and lungs.  After several weeks, the larvae migrate back into to the intestines to mature into adults. When the adult worms reproduce, their eggs will pass through the cat’s stool, completing the life cycle of the worm (VCA).

Other gastro-intestinal roundworms that may infect cats in various parts of the world include:

  • Ollulanus tricuspis (found in the stomach)
  • Gnathostoma spp
  • Physaloptera spp
  • Strongyloides spp


Roundworms are large-bodied worms, averaging about 3-6 inches in length.  Unlike most intestinal parasites, roundworms do not attach to the wall of the intestine, but rather they swim freely within the intestine.


Cats become infected by swallowing eggs of roundworm larvae.  The eggs can be found in the feces of infected cats or in the tissues of an atypical host (paratenic host). Common atypical hosts include earthworms, cockroaches, rodents, and birds.  Atypical hosts are not a common host for roundworms, so the eggs do not mature into adults, and instead serve as a worm transporter.  When a cat eats an atypical host, the worms can complete their life cycle.

Additionally, while in a current host’s body, roundworm larvae can become enclosed in a cyst and remain dormant inside a cat.  When a mother cat becomes pregnant, the larvae can break free of the cyst and be passed to the kittens through their mother’s milk.  This is known as trans-mammary infection, and is one of the most common forms of transmission in kittens.  Larvae can also be passed on to a kitten during pregnancy through the mother’s placenta.


Common signs of roundworms include a pot-bellied appearance, abdominal discomfort, depressed appetite, dull hair coat, vomiting and diarrhea, or poor growth.  If a cat has a large numbers of roundworms, they may cause life-threatening problems in kittens and in older cats.  Cats with a small number of worms may not show any signs of infection at all.  Look for adult roundworms in your cat’s feces or vomit.

Dangerous to Humans?

Roundworms can be a risk for humans.  The most common way that humans are infected is by accidentally ingesting eggs in soil that have been contaminated with cat or dog feces.  That being said, it is so important to wash your hands thoroughly and frequently!

To learn about the treatment and prevention of worms, check out Cat Treatment and Prevention.

Hookworm for cats

Hookworms are more frequently found in dogs rather than in cats, and the feline hookworms are usually less aggressive than the canine species.  These worms suck the blood from the tissues of their host and attach to the intestinal wall with their hook-like mouthpieces (VCA).  Hookworms have a long lifespan, and are able to live as long as the life of a cat.


Hookworms get their name from the hook-like mouthparts that they use to anchor themselves to the lining of the intestinal wall.  The worms are thread-like and about 1/8 inches long.  They are so small that they are barely able to be seen with the naked eye, and typically need a microscope to be seen.


Female hookworms pass hundreds of tiny eggs in a cat’s feces.  Larvae will hatch from the eggs and remain alive in the soil for weeks or even months.  A cat can ingest these larvae while grooming its paws, and the hookworm infection can begin.  The larvae will travel inside the cat’s body to the intestines where they will complete their life cycle.  Some may travel to the trachea or burrow into the cat’s skin and migrate to the lungs.  Once this happens, the cat will cough up and swallow the larvae, sending them to the intestines where they can mature.  It typically takes about 2-3 weeks for a female larvae to mature and lay eggs.


Common signs to look for a hookworm infestation include anemia, digested blood in the stool (a black and “tarry” substance), a poor coat, and weight loss.  A large infestation can be indicated by skin irritation and itching, especially of the paws.  The hookworm larvae burrow into the skin causing irritation.

Feline hookworms feed along the lining of the small intestine, sucking blood and injecting an anti-clotting substance at each feeding site.  This prevents the cat’s blood from clotting, resulting in blood loss and bleeding into the bowel from the feeding sites.  Anemia due to blood loss is more severe in kittens than in adult cats.

Dangerous to Humans?

Feline hookworms cannot infect humans internally, however, the hookworm larvae can burrow into a human’s skin and cause a disease called cutaneous larval migrans (ground itch).  This is rarely seen when good hygiene is practiced, and only occurs when the skin comes into contact with moist, larvae-infected soil.  Common symptoms humans may experience include itchiness, skin irritation, and long, linear lesions.

To learn about the treatment and prevention of worms, check out Cat Treatment and Prevention.

Tapeworm for cats

Tapeworms live in the small intestine with their heads implanted into the mucous membrane lining of the gastrointestinal tract.  They absorb nutrients from their host, and as the segments farthest from the head mature, they break off and pass in the cat’s feces (Cornell University, 2018).

Other tapeworms that occur in some countries include:

  • Diphylobothrium latum (fish are intermediate hosts)
  • Spirometra spp (amphibian, reptiles and rodents are intermediate hosts)
  • Diplopylidium spp (reptiles are intermediate hosts)
  • Joyeuxiella spp (reptiles are intermediate hosts)
  • Echinococcus multilocularis (rodents are intermediate hosts)

(International Cat Care)


Tapeworms are long, flat worms with many body segments that often resemble tape or ribbon.  Their small heads are attached to many segments, each filled with eggs.  The mature segments that contain the eggs are released in the cat’s feces and look like small grains of rice.  Most feline tapeworms are about 8 inches when they are fully grown, however they can grow to 20 inches long.  The eggs can often be seen on the hair around the anus of the cat or in the feces.


Taenia taeniaeformis tapeworms need an intermediate host to first eat the worm’s eggs from the environment.  A cat will then become infected after eating the intermediate host.  Intermediate hosts range from small rodents like mice and rats to birds.

Dipylidium caninum is transmitted to cats through fleas.  Immature flea larvae ingest the tapeworm’s eggs, and then pass on the infection to a cat when the flea is swallowed during grooming.


If a cat has a tapeworm infestation, you may see dried, white colored worm segments in the feces or stuck to the fur.  Cats may bite or groom their backside frequently, or consistently drag their bottom across the floor for itching relief.

Dangerous to Humans?

Tapeworms are typically not contagious to humans, however good hygiene is always best practice, and will virtually eliminate any risk of infection.  Frequently wash your hands and shower regularly, and read our blog for more good hygiene tips!

To learn about the treatment and prevention of worms, check out Cat Treatment and Prevention.

Lungworm for cats

Lungworm is a parasite that lives in the lungs and airways of cats.  Once inside a feline’s body, the adult worms lay eggs that hatch into larvae, and tunnel their way through the lung tissue.  These parasites cause severe breathing problems for cats as they live in the respiratory system.


Lungworms are long, stringy worms that are typically 1 to 4 centimeters long, and the female lungworms are significantly longer than the male lungworms.


Feline lungworm is most commonly carried by slugs and snails.  Cats can become infected by eating an infected mollusc or by eating a rodent or bird that has recently eaten an infected snail or slug.  Once ingested, the parasites migrate from the intestines to the lungs through the bloodstream, where they then mature and release eggs in the lungs.  The eggs are coughed up or passed in the cat’s feces, which can then be eaten by rodents, snails, birds, etc. and thus complete the life cycle.


Lungworms mainly cause severe breathing and respiratory problems.  Your cat may experience coughing and shortness of breath, wheezing, or feline asthma. The coughing is caused by the larvae that are laid in the airway, causing difficulty in breathing and an abundance of mucus.  If left untreated, symptoms may worsen, including fluid-build up in the lungs or pneumonia.

Dangerous to Humans?

It is rare that lungworms will be spread from a cat to a human, but it is not impossible.  Practice good hygiene by thoroughly washing your hands and bathing, and do not consume raw molluscs.

To learn about the treatment and prevention of worms, check out Cat Treatment and Prevention.

Eyeworm for cats

Eyeworms are a whitish parasite that move in a snake-like motion across a cat’s eye.  There can be up to as many as 100 eyeworms in the tear ducts and on the conjunctiva under the eyelids (Merck Veterinary Manual).  The species is commonly found in western North America, and there are more cases around late spring and summer when flies are more active.


Adult eyeworms are thin and about 0.25 to 0.75 inches long.  The eggs and larvae can only be seen under a microscope from a tear or secretion sample.


Flies are the main intermediate hosts that transfer worm larvae onto a cat’s eye.  Eyeworm larvae grow in a fly’s body for about 30 days, and then migrate to the fly’s mouth.  When a fly lands on a cat’s eye to feed on the secretions of the eyes,  the larvae move out of the fly’s mouth and into to the eye of the new host.  In 3-6 weeks, the larvae develop into adults.


Generally, cats will not show many signs if there is an infestation, however due to the irritation to the eye, cats may produce more tears, may be sensitive to light, and occasionally develop conjunctivitis (inflammation of the mucous membranes of the lids).  There may be clouding of the corneas, and if left untreated, blindness (Pet Coach).

Dangerous to Humans?

An eyeworm infection in humans is extremely rare, but not impossible.  It is extremely rare for a person to have a fly near his or her eyes long enough for the fly to deposit worm larvae.

To learn about the treatment and prevention of worms, check out Cat Treatment and Prevention.

Heartworm for cats

Cats are an atypical host for heartworms and most worms do not survive to the adult stage in a cat.  Felines will usually have one to three worms and often go undiagnosed.  Even though cats do not get hundreds of worms like dogs, even immature worms can cause severe damage and a condition called Heartworm Associated Respiratory Disease (HARD) (American Heartworm Society, 1970).  HARD is a lung disease that develops as a direct result of heartworms, and often causes coughing, lethargy, difficulty breathing, and in severe cases, convulsions.


Heartworms are foot-long worms that live in the heart, lungs, and associated blood vessels of cats.


Adult female heartworms living in an infected host will lay eggs that grow into baby worms called microfilaria.  When a mosquito bites an infected cat to take a blood meal, it ingests the baby worms that turn into larvae over 10 to 14 days.  When the mosquito then bites another cat, the larvae are deposited onto the new cat’s skin and migrate into the body through the bite wound.  Once inside the cat’s body, it takes about 6 months for the larvae to mature and grow into adults.  Once adults, the heartworms can live for 2 to 3 years in cats.


Cats are not a typical host for heartworms, so many worms do not survive to the adult stage in cats.  That being said, heartworm disease often goes undiagnosed in cats since most do not show symptoms.  If they do show signs of the disease, symptoms may include coughing, asthma-like attacks, vomiting, lack of appetite, or weight loss.  Some cats may have a hard time walking, may have seizures, or may have fluid build up in the abdomen.  Unfortunately, the first sign can often be sudden collapse or sudden death.

Dangerous to Humans?

Heartworms can live in other mammal species including humans, but it is extremely rare.

To learn about the treatment and prevention of worms, check out Cat Treatment and Prevention.


Can cat worms be transfered to dogs?

Yes!  Many worms can be transferred between different species, so if you have a cat that is infested with worms, it is a good idea to keep your animals separated until the infestation has been treated.

What does lungworm look like in cats?

Lungworms are long, stringy worms that are typically 1 to 4 centimeters long, and cause severe breathing and respiratory issues.

Can roundworms infect humans?

Yes.  Roundworms can infect humans if their eggs are ingested.  Wash your hands thoroughly and frequently to avoid a parasitic infection.

Can heartworm be passed from cat to cat?

Heartworms are not transmitted directly from one cat to another cat.  A cat must be bitten by an infected mosquito in order to become infected.

What do tapeworms do to cats?

In the case of a tapeworm infestation, cats may bite at or groom their backside frequently.  They may also drag their bottom across the floor for itching relief.


What causes roundworms in cats?

Cats can become infected with a roundworm by swallowing eggs or larvae found in the feces of infected cats or in the tissues of earthworms, rodents, and birds.

How do cats get eyeworm?

Flies are the main intermediate hosts that transfer worm larvae onto a cat’s eye. When a fly lands on a cat, the larvae move out of the fly’s mouth and into to the eye of the cat.