ISSN 2398-2950      

Giardia felis


Synonym(s): G. felis, Giardia duodenalis, G. duodenalis Assemblage F, Giardia lamblia




  • Within the Excavata. phylum Metamonada, and the order Diplozoa.
  • The species G. duodenalis (syn. Giardia lambliaGiardia intestinalis) is broken into 8 groups called assemblages based on various molecular genetic markers. These Assemblages are designated by letters:
    • The one most commonly found in cats is Assemblages F.
    • Occasionally, cats are also found infected with Assemblage A that has been reported from many different animals and humans, Assemblage B that is for the most part restricted to human hosts.
    • Assemblage B is found mainly in people. 
    • Assemblage A has been reported from a number of different animal types and is the only Assemblage that appears to be readily shared by hosts in disparate mammalian groups. 
  • There are other distinct species recognized in other hosts: Giardia microti and Giardia muris in rodents; Giardia psittaci and Giardia ardeae in birds; and Giardia agilis in amphibians.

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Clinical Effects




  • Intestinal tract: surface of villi of duodenal and jejunal intervillar spaces.


  • Resistant stage.
  • Environment: in water or moist material.
  • Infective stage to new host.
  • Cat, humans, and other species: cats may on occasion be passing cysts of Assemblages (A and B) that could show varying degrees of cross-infectivity.


  • Giardia lifecycle Lifecycle: Giardia canis - diagram .
  • Trophozoite.
  • Cysts are passed 1-2 weeks after infection.


  • Direct feco-oral contamination: ingestion of cysts in feces or on objects contaminated with feces.
  • Water-borne: cysts survive several weeks in cool water but, while water-borne epidemics occur in man, their relevance to cats is far less clear and presumed less than feco-oral transmission.

Pathological effects

  • Polymorphonuclear leukocyte infiltration in lamina propria.
  • Increase in intraepithelial lymphocytes.
  • Intestinal secretory antibodies (IgA, IgG) important in immune protection which develops following infection, but protection is not absolute.
  • Steatorrhea: correlated with decrease in pancreatic lipase (mechanism?).
  • Decreased disaccharidases and brush border enzymes.
  • Malabsorption: due to decreased absorptive area and increased immature cells, villous atrophy and increased crypt mitotic activity:
    • Immune response and inflammation may contribute to villous atrophy.
    • Considerable shortening of microvilli.
  • Vacuolation of epithelial cells.

Other Host Effects

  • Giardia use their sucking disk to attach, detach and re-attach themselves to the brush border of the epithelial cells Giardia: depressions on intestinal surface .
  • Trophozoites may carpet the intestinal villi.
  • Rim of adhesive disk displaces and distorts microvilli leaving 'footprint' shapes of the disk in the brush border Giardia: depressions on intestinal surface .


Control via animal

  • Treatment of infected cats: not 100% effective.
  • Separation of infected cats.
    Asymptomatic carriers common and direct feco-oral contamination hard to break, and water-borne transmission a possibility.

Control via chemotherapies

  • No licensed claim for use of chemotherapeutic agents against giardiasis in cats; and only in Great Britain is fenbendazole approved for use in cats. 
  • Treatment efficacy is less than 100%; probability of reinfection high. The concern as to the potential of any infection being a possible source of a zoonotic agent has led to the proposal that all cases, with or without signs, should be treated. The trouble is some cats will not clear after treatment, and some may not clear after several treatments. Also, there is a good chance that the Assemblage present is a feline associated Assemblage that is not a zoonotic agent. Therefore, if a case does not clear after treatment, there may be need to consider the magnitude of the risk posed by the specific circumstances and a decision made as to whether further treatment is actually warranted on an individual basis.
  • Fenbendazole Fenbendazole 50 mg/kg every TID-BID for 5 days.
  • Metronidazole Metronidazole  25 mg/kg BID for 5 days.
    Drug resistance is known in human strains.
  • Ronidazole (not licensed for dogs) 30-50 mg/kg BID for 7 days.
    Ronidazole at 40-54 mg/kg BID for several days has been reported to cause neuro-toxicosis in some cats.
  • Secnidazole 30 mg/kg one time; salivation occurs for several minutes after administration.
  • Albendazole Albendazole (not licensed for cats) 25 mg/kg BID for 2-5 days.
    Albendazole is associated with serious side-effects (bone marrow suppression) and should not be used.

Control via environment

  • Desiccation.
  • Disinfection (sodium hypochlorite).
  • Desiccation is lethal to cysts and rate of death is increased at temperatures greater than 30°C.
  • Steam cleaning kills cysts.
  • Hygiene and removal of feces.
  • Chemicals:
    Cysts are relatively resistant to chemicals.
    • Wash animals and treat before return to cleaned area.
      • Quaternary ammonium compounds: effective within 1 minute on cleaned surfaces.
      • Sodium hypochlorite: cysts in water are sensitive to chlorine treatment but destruction is very dependent on concentration, time, pH, temperature.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Da Silva A S, Castro V S, Tonin A A et al (2011) Secnidazole for the treatment of giardiasis in naturally infected cats. Parasitol Int 60 (4), 429-432 PubMed.
  • Rosado T W, Specht A, Marks S L (2007) Neurotoxicosis in 4 cats receiving ronidazole. JVIM 21 (2), 328-331 PubMed.
  • Gookin J L, Copple C N, Paich M G et al (2006) Efficacy of ronidazole for treatment of feline Tritrichomonas foetus infection. JVIM 20 (3), 536-543 PubMed.
  • Scorza A V, Radecki S V, Lappin M R (2006) Efficacy of a combination of febantel, pyrantel, and praziquantel for the treatment of kittens experimentally infeted with Giardia species. J Feline Med Surg (1), 7-13 PubMed.
  • Scorza A V & Lappin M R (2004) Metronidazole for the treatment of feline giardiasis. J Fel Med Surg (3), 157-160 PubMed.
  • Stokol T, Randolph J F, Nachbar S et al (1997) Development of bone marrow toxicosis after albendazole administration in a dog and cat. JAVMA 210 (12), 1753-1756 PubMed.

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