Please enable JavaScript!
Bitte aktiviere JavaScript!
S'il vous plaît activer JavaScript!
Por favor,activa el JavaScript!

This article offers a list of the most common parasites of cats, both external (ectoparasites) and internal (endoparasites) parasites. 

Detail information on their biology and control (life cycle, anatomy, prevention, chemical control, etc.) is available in specific articles in this site. To visit these specific articles click the corresponding link, navigate through the menu, or use the site map.

Three letters summarize important characteristics of each parasite:

  • «H» to «HHHHH» indicates how harmful they are for cats or kittens. The more H, the more harmful.
  • «F» to «FFFFF» indicates how frequent these parasites are. The more «F», the more frequent.
  • «C» to «CCCCC» indicates how contagious for humans are these parasites through direct or indirect contact with the cats. The more «C», the more contagious, regardless of the seriousness of these cat parasites for humans: some are rather benign, other very harmful.

For a general introduction to parasites click here.

External Parasites (ectoparasites)

Biting insects (hematophagous), i.e. they suck blood

  • Fleas  HHHH-FFFFF-CCCCC. Probably the most frequent and universal parasite of cats worldwide, and potentially harmful. Not dangerous for humans, but extremely annoying. Widespread resistance to several insecticides.
  • Stable flies  H-FF. Usually a minor problem for cats. Worldwide but mainly in rural regions. May transmit various diseases.
  • Bed bugs  H-FF. An increasing problem, but less for the cats than for their owners. Worldwide.
  • Mosquitoes  HH-FFF. Usually not a serious threat by themselves for cats, but are vectors of several diseases, notable heartworms (Dirofilaria spp). Worldwide.
  • Horseflies  H-FF. Usually a minor problem for cats. Worldwide but mainly in rural regions. Their bites can be quite painful and are also vectors of various diseases.

Non-biting insects, do not suck blood

  • Houseflies  H-FFFFF. Usually a minor problem for cats. Worldwide but mainly in rural regions. Widespread resistance to several insecticides. May transmit some cat diseases.
  • Filth & nuisance flies  H-FF. Usually a minor problem for cats, worldwide but mainly in rural regions. Widespread resistance to several insecticides.
  • Lice  HH-FF-C Usually not a serious threat, neither for pets, nor for humans. Some species do suck blood.
  • Human bot flies, Dermatobia  H-F. A problem in many regions of Central and South America.
  • Screwworm flies  HHH-FFUsually not a very serious problem for cats, unless occasionally in endemic regions in tropical and subtropical countries.

Ticks & mites

  • Ticks  HH-FF-C. Usually not a big issue for cats unless in rural regions. Ticks transmit many diseases.
  • Mites  HH-FF-CC. Occur worldwide but usually not the worse problem in cats.

Additional information on the general features of insects, ticks, and mites is available in this site.

Internal parasites (endoparasites, worms, helminths)

Predilection sites are indicated in braquets.

Gastrointestinal roundworms (nematodes)

  • Ancylostoma spp  HHH-FFF-CC. Hookworms. (Small intestine and larva migrans). A serious threat for cats. Worldwide, with different regional incidence for the various species.
  • Aonchotheca putorii (=Capillaria) putorii  H-F. (Stomach). A minor problem for cats. Worldwide, with regional incidence.
  • Capillaria hepatica   H-F Hairworms. (Liver). Not a major problem. Worldwide, but with different regional incidence.
  • Gnathostoma spinigerum  HH-F (Stomach and larva migrans). Usually a secondary problem in some endemic hot and humid regions. 
  • Gongylonema spp  H-F (Esophagus and stomach). Not a major threat for cats. Worldwide, but only regionally relevant.
  • Ollulanus tricuspis   H-FF. The cat stomach worm. (Stomach) Minor occasional problem in endemic zones.
  • Physaloptera spp  H-(Stomach and small intestine). Usually a minor problem in endemic regions.
  • Strongyloides spp  HHH-F-CC Threadworms, pinworms. (Small intestine and larva migrans). A serious threat for cats, worldwide but especially in warm and humid rergions.
  • Toxascaris leonina  H-FF (Small intestine). Usually a minor problem, worldwide.
  • Toxocara cati  HHHHH-FFFF-CCC The cat roundworm. (Small intestine and larva migrans). One of the most serious threats for cats, especially for kittens. Worldwide and very frequent everywhere.
  • Trichuris spp  HH-FF Whipworms. (Large intestine and larva migrans). Not the major problem worldwide, but occasionally serious.
  • Uncinaria stenocephala  HH-FFF-CC The fox hookworm. (Small intestine and larva migrans). A significant threat worldwide, but usually less serious than other hookworms (e.g. Ancylostoma spp).

Respiratory roundworms (nematodes)

  • Aelurostrongylus abstrusus  H-F. (Bronchi, alveoli). Usually a minor problem. EWorldwide, with regional incidence.
  • Eucoleus spp (=Capillaria spp)  H-F. Hairworms, nasal worms. (Nasal cavities). Usually a minor issue. Worldwide, but with different regional incidence.

Roundworms (nematodes) in the eyes, skin, heart and other organs

  • Dioctophyma renale HH-F. The giant kidney worm. (Kidneys). Occasionally in cats, in endemic zones.
  • Dirofilaria spp  HHHH-FFF. Dog Heartworms. (Lung arteries, occasionally heart). A serious threat for cats. But less abundant and threatening than for dogs. Worldwide, but especially in tropical and subtropical regions with abundant mosquitoes. 
  • Pearsonema spp (= Capillaria spp)  H-F. Hairworms, bladder worms. (Bladder). usually a minor problem. Worldwide, with varying regional incidence.
  • Thelazia spp  H-F. Eyeworms. (Eyes). Occasional problem in cats. Worldwide but with endemic distribution.
  • Trichinella spp  H-FF. (Muscle, small intestine). A minor health problem for cats. Worldwide, but only in endemic zones, mainly in rural regions.

Flukes (trematodes, flatworms) 

  • Alaria spp  H-F. (Small intestine). Usually a minor issued for cats. Worldwide, but only in endemic regions.
  • Dicrocoelium spp  H-FLancet flukes. (Bile ducts and gall bladder). An occasional problem for cats. Worldwide.
  • Fasciola hepatica  HH-F. The common liver fluke. (Biliary ducts and gallbladder). Mostly an uncommon and not very threatening problem for cats. Worldwide, but mainly in rural regions.
  • Opisthorchis felineus  H-F. The cat liver fluke. (Hepatic and biliary ducts). Not a serious threat. Worldwide but only in endemic regions.

Tapeworms (cestodes)

  • Dipylidium caninum  H-FFF-CCC. The flea tapeworm. (Small intestine). Only occasionally in cats and not seriously harmful.
  • Echinococcus multilocularis H-F-CCC. The small fox tapeworm. (In cats, small intestine). Rather benign for cats, but a serious threat for livestock and humans. Worldwide but not very frequent.
  • Mesocestoides spp HH-F. (Small intestine). Usually not a serious threat for cats. Worldwide, but not very frequent. 
  • Taenia spp  H-FFFFF. (In cats, small intestine). Usually not seriously harmful for cats, but a significant threat for livestock (cysticercosis). Quite frequent worldwide.


  • Linguatula serrata H-F. Tongue worms. (Nasal cavities and pharynx). Usually a minor problem. Worldwide in subtropical regions, rather occasional.

Other interesting articles