Cat Internal Parasites

Domestic cats can be infested by a large range of parasite species. Parasitic infestations may cause very different clinical signs, from mild gastro-intestinal disorders and failure to thrive, to anemia, particularly in kittens with heavy parasitic infestation. Parasites of cats are a threat for both animal and human health. Diarrhea, vomiting, loss of appetite and pale lips and gums are the frequently found signs of internal parasite infestation in cats.


Different species of ascarids, commonly known as roundworm may affect the small intestine of cats. Toxocara cati and Toxocara leonina are more commonly found in cats living outdoor than in household cats. Prevalence of T. cati in cats has been estimated to vary from 0.8 to 59.3% in different parts of the world. Ascarids live free in the lumen of the small intestine feeding on its content. Mild infections are usually not accompanied by clinical signs either in larval migration or in patent infections. When the number of canine roundworms is moderate-high, larval migrations can cause cough, frothy nasal discharge, pneumonia and edema of the lungs. Kittens with heavy infections may expel a large mass of worms in vomitus. In cats the infection can be seen as an enteritis with vomiting and diarrhea, even bloody.

The parasites are responsible for human visceral/ocular and cutaneous larva migrans and are of great public health significance in their causing the most widespread and economically important zoonoses.

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Cats can be infected with heartworms Dirofilaria immitis and Dirofilaria repens. Infected cats can have chronic coughing, labored breathing, vomiting that is not associated with food intake, and diarrhea. Some may die suddenly without any warning signs. In nonfatal cases of acute infection, cats can transition to the chronic stage or become fully asymptomatic but later revert to the chronic form of the disease. Although humans are not suitable hosts for Dirofilaria species, immature D. immitis worms can reach a branch of the human pulmonary artery, triggering an inflammatory response that destroys the worms, occasionally resulting in pulmonary nodules. D. repens worms cause subcutaneous nodules and can reach the ocular region in human patients. Both species can infect other organs but only incidentally.4 Recently, the almost unknown heartworm Angiostrongylus chabaudi, recorded only in the last century in wildcats until recently, has been found in two domestic cats from Italy.8

Aelurostrongylus abstrusus is a roundworm which is most commonly found in the form of worm larva in snails, a common food source to mice, birds and rodents. About 50 percent of free roaming cats are infected with this "cat lungworm." The infection typically occurs by the ingestion of infected mice, birds or rodents. Mild infections often have only a few signs, however, heavy infections can cause severe bronchopneumonia. Cats can have rapid, open-mouthed abdominal breathing.


Cats are principal definitive host of Taenia taeniaeformis, or cat tapeworm. The eggs of this parasite might be less sensitive to hot and dry weather condition due to the special defecation behavior of domestic cats which usually bury their droppings into loose soil where taeniid eggs are less exposed to adverse weather conditions.

Helminth and fungus concomitant infection are common in developing countries. In China, cats are an important infection source of Sporothrix schencki and Taenia taeniaeformis and it has been speculated that the fungus and the tapeworm co-infection might take place in farmers, but influence of helminth infection on sporotrichosis is not understood.


Hookworms have been regarded as the most faithful intestinal parasites of dogs and cats. Indeed, they are responsible for developmental impairment, severe clinical signs and high death rate, especially in young pets. These worms live anchored to the gut mucosa by their oral capsule and have a relevant blood-sucking activity. Cats affected by Ancylostoma tubaeforme suffer with enteritis, blood loss, diarrhea, reduced weight, regenerative anemia, and even death.

In cats medications containing pyrantel and praziquantel has high efficacy against ascarids and hooworms. Controlling ascaridosis and ancylostomosis in pets is crucial to reduce infection risk for other companion animals and to minimize public health hazards.


Whipworms (Trichuris vulpis) are major parasites of gastrointestinal tract of dogs. Cats are most often infected with Trichuris campanula and Trichuris serrata species of whipworms. Whipworms are much less common in cats than in dogs and produce milder symptoms. There have been no reports of human infection with cat trichurids.

Liver Parasites

Cholangitis is an obstruction of the biliary tract most commonly from a gallstone, bacterial infection, neoplasm, or liver flukes such as Platynosomum species and Amphimerus pseudofelineus. This parasitic disease is also known as "lizard poisoning" as it is assumed that most affected cats acquire the parasite by eating infected lizards. The fluke resides in the gallbladder and biliary ducts of the infected cat creating inflammation within bile ducts and portal areas. Cats with acute cholangitis suddenly stop eating, may have vomiting, diarrhea, and a fever.1

Protozoal Parasites

Potentially zoonotic Giardia is now considered the most common enteric parasite in well cared for dogs and cats in developed countries. Animal-to-animal and animal-to-human transmission are major concerns. In cats, giardiasis is associated with a wide spectrum of clinical signs and varies from asymptomatic to severe gastrointestinal disease. Loose or watery diarrhea with increased frequency is the predominant clinical sign, while vomiting is observed in about 20 percent of infected cats. The duration of abnormal clinical signs vary between days and years.

Two species of Cystoisospora (previously called Isospora) occur in cats: Cystoisospora felis and Cystoisospora rivolta, which are intracellular parasites with a life cycle frequently involving mice or other rodents as their hosts. Almost all cats will become infected with the parasite in their lifetime through the ingestion of infective oocysts from the environment or eating an infected prey. Infections frquently occur where cats are housed together, in shelters, catteries, or pet stores. Clinical signs range from hemorrhagic enteritis, emaciation, and death, depending on the severity of the infection.


  1. Percutaneous Ultrasound‐guided Cholecystocentesis and Bile Analysis for the Detection of Platynosomum spp.‐Induced Cholangitis in Cats. L. Köster, L. Shell, Illanes, C. Lathroum, K. Neuville, and J. Ketzis
  2. Updates on feline aelurostrongylosis and research priorities for the next decade. Hany M. Elsheikha,corresponding author Manuela Schnyder, Donato Traversa, Angela Di Cesare, Ian Wright, and David W. Lacher
  3. Parasites of domestic owned cats in Europe: co-infestations and risk factors. Frédéric Beugnet,corresponding author et al.
  4. Human and Animal Dirofilariasis: the Emergence of a Zoonotic Mosaic. Fernando Simón,corresponding author et al.
  5. Taenia taeniaeformis in Rat Favors Protracted Skin Lesions Caused by Sporothrix schenckii Infection: Dectin-1 and IL-17 Are Dispensable for Clearance of This Fungus. Xiaohui Zhang et al.
  6. Prevalence and diagnosis of Giardia infection in dogs and cats using a fecal antigen test and fecal smear. Merle E. Olson, Nancy J. Leonard, and Jessie Strout
  7. Pet roundworms and hookworms: A continuing need for global worming. Donato Traversacorresponding
  8. Novel Molecular Assay for Simultaneous Identification of Neglected Lungworms and Heartworms Affecting Cats. Angela Di Cesare,corresponding author, et al.
  9. Consultations in Feline Internal Medicine, Volume 6 -, Volume 6. John R. August
  10. The Encyclopedia of the Cat, Angela Sayer

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