Common Feline Parasites


Whether your cat stays indoors or outdoors, all cats are at risk for internal and external parasites. Recognizing the signs of parasites and knowing their life cycles could help maintain your cat’s health. Dr. Sina Marsilio, internist and researcher at the Texas A&M College of Veterinary Medicine’s Gastrointestinal Laboratory, explained the most common feline parasites, including fleas, ticks, roundworms, hookworms, tapeworms, and heartworms.

“The parasites most common in cats depends on where the cat lives and if it is an indoor or outdoor cat. Generally, indoor cats have fewer parasites than outdoor cats,” she said. “The most common external parasites affecting the skin are fleas and ticks. While there many different internal parasites, most of them affect the gastrointestinal tract. However, especially in Texas, we need to be aware of heartworms in cats, which mostly affect the heart and lung vessels.”

All cat owners should treat their pet for fleas and ticks. If left untreated, these pesky parasites can infest not only your cat but your house and yard as well. Cats can acquire fleas from other animals, including wildlife in the backyard or another cat or dog in the household. “Fleas live in the cat’s fur where it is warm and moist,” Marsilio said. “They stick to the cat’s skin and suck blood. These bites can cause itching and cats respond by licking and scratching. The skin around the back of the neck and the top of the tail head is most commonly affected.”

Severe flea infestation may lead to anemia because the fleas suck more blood than the cat can produce, especially in kittens. In addition, your cat may be allergic to the fleas’ saliva, which can lead to a condition called flea allergy dermatitis. Cats with a flea allergy may obsessively scratch, leaving the skin hairless, red, and crusty. Fleas also carry tapeworm eggs and bacteria, which can lead to other health issues.

Internal parasites, such as roundworms, hookworms, and tapeworms, affect the gastrointestinal tract and can be wormlike or single-celled microscopic organisms called protozoans. “Gastrointestinal parasites primarily cause signs of gastrointestinal disease, including loss of appetite, weight loss, vomiting, diarrhea, mucoid or bloody feces, and pot-bellied appearance,” Marsilio said. “Any blood loss caused by the parasite can lead to anemia. Vomiting and diarrhea can cause dehydration, which makes your cat susceptible to various other bacterial and viral infections. Some gastrointestinal parasites may even be zoonotic, meaning they can be transferred from animals to humans.”

Common internal feline parasites include:


  • Resemble spaghetti, three to four inches long
  • Commonly infect outdoor cats from hunting and eating infected mice
  • Adult cats can become infected from ingesting an infected cat’s feces
  • Can be transferred to kittens through the mother’s milk


  • Primarily reside in the small intestine and feed on the cat’s blood
  • An infestation can lead to life-threatening anemia, especially in kittens
  • Can be transmitted from cat to cat through feces


  • Long and flat worms, four to 28 inches in length
  • Can be transmitted by ingesting immediate hosts, such as fleas or rodents


  • Larvae are transmitted via mosquitoes
  • No proven treatment for adult heartworm disease in cats
  • Heartworm prevention is important because treatment can be long term and expensive

“Even though dogs are at greater risk for a heartworm infection, they do occur in cats. Heartworm disease might be without any clinical symptoms, but when clinical signs occur, they are usually severe to even life threatening,” Marsilio said. “Cats with heartworm disease may show coughing, wheezing, difficulty breathing, vomiting, or neurological signs such as falling over, collapsing or having seizures.

If you think your cat has a parasite, including fleas and ticks, be sure to visit your veterinarian for treatment. “In general, your veterinarian is always the best source of information,” Marsilio said. “They know about you and your cat’s history and lifestyle, and they can determine the specific risks for your pet.”

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Dr. Sina Marsilio is currently looking for fresh fecal samples from healthy cats and cats with diarrhea or other gastrointestinal signs such as vomiting, loss of appetite, or weight loss. The Gastrointestinal Laboratory offers several tests free of charge in return for a fecal sample from your cat and a completed questionnaire. If you are interested in participating in Dr. Marsilio’s study, please contact her via email.

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