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Cited by 37Parasitic Infections and DiagnosticsHelminth infection and controlVeterinary medicine and infectious diseases

Evaluation of fenbendazole for treatment of Giardia infection in cats concurrently infected with Cryptosporidium parvum.

Open access
Keith, Carey L., Radecki, Steven V., Lappin, Michael R.·2003·American Journal of Veterinary Research
DOI 10.2460/ajvr.2003.64.1027
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Abstract

OBJECTIVE: To determine whether fenbendazole effectively eliminates Giardia organisms from chronically infected cats that have a concurrent Cryptosporidium parvum infection. ANIMALS: 16 clinically normal cats. PROCEDURE: Eight cats with chronic concurrent Giardia and C parvum infections received fenbendazole (50 mg/kg, PO, q 24 h) for 5 days (treatment-group cats). Feces from each cat were collected and processed 3 days weekly for 23 days after treatment. By use of an immunofluorescent assay for detection of Giardia lamblia cysts and C parvum oocysts, organism numbers were counted and scored. Fecal results from treatment-group cats were compared with those of 8 untreated cats with Giardia infection but no C parvum infection (control-group cats). RESULTS: Four of 8 treatment-group cats had consistently negative results for Giardia infection after treatment. These 4 cats had consistently positive results for C parvum oocysts prior to treatment and consistently negative results after treatment. One treatment-group cat had positive results for cysts on all fecal samples, and 3 treatment-group cats had 1 to 3 negative results and then resumed shedding large numbers of cysts; each of these cats had consistently positive results for C parvum oocysts. When compared with control-group cats, treatment-group cats shed less Giardia cysts during week 1 after treatment but not during week 2. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of fenbendazole decreases Giardia cyst shedding to less than detectable numbers in some cats. In our study, persistent C parvum infection may have been associated with failure of fenbendazole to eliminate Giardia infection.

AI snapshot

Written from the paper’s full text.

TL;DR

In cats chronically infected with Giardia and concurrently carrying Cryptosporidium parvum, a five-day fenbendazole course reduced Giardia cyst shedding for part of the follow-up period, but only half of treated cats cleared Giardia by three weeks. The authors conclude fenbendazole may help some cats but is not uniformly effective, and they note that subclinical infection and assay detection limits complicate interpretation.

Key findings

  • Among 8 treated cats, 4 had no detectable Giardia after 5 days and remained negative through the 3-week study; these cats also changed from C parvum-positive to C parvum-negative.
  • One treated cat had a temporary drop in Giardia cysts but was shedding large numbers again by study day 9, while 3 others briefly tested negative and then resumed heavy shedding; C parvum detection paralleled Giardia in these cats.
  • All 8 untreated control cats remained Giardia-positive and C parvum-negative throughout.
  • By ANOVA, treated cats shed significantly fewer Giardia cysts from late week 1 until early week 3; by Wilcoxon rank sum test, the significant reduction was in week 2, and no significant difference remained in week 3 by either test.

Methods

  • Sixteen laboratory-reared cats aged 1–2 years were used: 8 were coinfected with Giardia and a human genotype 2 C parvum isolate for about 3 months, and 8 controls were inoculated with the same Giardia strain but not C parvum; treated cats received fenbendazole 50 mg/kg PO every 24 hours for 5 days.
  • Feces were collected 3 days per week for 23 days after treatment began and tested by commercial direct immunofluorescence for Giardia cysts and C parvum oocysts; cyst counts were converted to a 0–4 score.
  • Repeated-measures ANOVA and Wilcoxon rank sum test compared treated versus control cyst shedding, with P < 0.05 considered significant.

Limitations

  • Stated: because infections were subclinical, the study cannot determine whether fenbendazole reduces clinical signs of giardiasis.
  • Stated: immunofluorescence detection limits were 100 C parvum oocysts/mL and 100 Giardia cysts/mL, so apparent clearance may reflect suppression below detection; more sensitive quantitative methods such as PCR are recommended.
  • Stated: possible treatment failures could involve reinfection, temporary drug suppression, C parvum coinfection, or differences in drug susceptibility among Giardia strains; evident: small groups (8 per group) and a short 3-week follow-up limit precision and durability conclusions.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.2460/ajvr.2003.64.1027

Cites

25 of 25 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

3 of 15 cited sources checked · 0 supported · 0 flagged · accuracy not yet measured

  • Findingown data

    When compared with results from control-group cats by use of an ANOVA, fenbendazole treatment-group cats began shedding significantly fewer Giardia cysts near the end of week 1, which continued until the start of week 3.

    “When compared with results from control-group cats by use of an ANOVA, fenbendazole treatmentgroup cats began shedding significantly fewer Giardia cysts near the end of week 1, which continued until the start of week 3 (Fig 1).”
    Quote in the paperSubstantial claim
  • Findingown data

    In week 3, there was no significant difference in cyst numbers between the treatment and control groups by use of either statistical method.

    “In week 3, there was no significant difference in cyst numbers was detectedbetween the treatment and control groups by use of either statistical method.”
    Quote in the paperNot a substantial claim
  • Findingown data

    Cryptosporidium parvum oocysts were not detected in any fecal sample from the control group cats.

    “Cryptosporidium parvum oocysts were not detected in any fecal sample from the control group cats.”
    Quote in the paperNot a substantial claim
  • Findingown data

    One of the 8 treatment-group cats had a transient decrease in the number of Giardia cysts shed but resumed shedding large numbers of Giardia cysts by day 9 of the study.

    “One of the 8 treatment-group cats had a transient decrease in the number of Giardia cysts shed but resumed shedding large numbers of Giardia cysts by day 9 of the study.”
    Quote in the paperNot a substantial claim
  • Findingown data

    By retrospective evaluation of stored feces, the C parvum-infected cats had been infected with the Giardia sp for approximately 3 months prior to being treated in this study.

    “By retrospective evaluation of stored feces, it was determined that the C parvum-infected cats had been infected with the Giardia sp for approximately 3 months prior to being treated in this study.”
    Quote in the paperNot a substantial claim
  • Classified as probably not a substantial claim. 11
  • May combine two claims. 13

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The benzimidazoles fenbendazole, albendazole, and febantel have been successfully used to treat giardiasis in dogs.

    “The benzimidazoles, fenbendazole, albendazole, and febantel (a drug that is metabolized to fenbendazole) have been successfully used to treat giardiasis in dogs.8,10,11,14”
    Quote in the paperNot a substantial claim2 of 3 sources checked
    • cites [8] 8. Barr SC, Bowman DD, Heller RL, et al. Efficacy of albenda- zole against giardiasis in dogs. Am J Vet Res 1993;54:926-928. source
    • cites [10] 10. Barr SC, Bowman DD, Heller RL. Efficacy of fenbendazole against giardiasis in dogs. Am J Vet Res 1994;55:988-990. source

      The Abstract reports successful fenbendazole treatment in dogs, and the Additional information section reports that albendazole removed Giardia cysts from infected dogs. The copy does not address febantel or the claim that it is metabolized to fenbendazole (searched: febantel). No page number was provided for these passages. (LLM, conf=0.88)

      Experimental — accuracy not yet measured
    • cites [11] 11. Zajac AM, LaBranche TP, Donoghue AR, et al. Efficacy of fenbendazole in the treatment of experimental Giardia infection in dogs. Am J Vet Res 1998;59:61-63. source

      The results and Discussion report that fenbendazole was effective against Giardia infection in dogs. The paper does not report successful treatment with febantel or establish that it is metabolized to fenbendazole; albendazole appears in a cited reference, but the paper does not itself report its treatment results. Page numbers are unavailable in our copy. (LLM, conf=0.86)

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    It was previously shown that C parvum coinfection potentiated Tritrichomonas foetus infections in cats.

    “It was previously shown that C parvum coinfection potentiated Tritrichomonas foetus infections in cats.17”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [17] 17. Gookin JL, Levy MG, Law JM, et al. Experimental infecton of cats with Tritrichomonas foetus. Am J Vet Res 2001;62:1690-1697. source

      The Discussion (page not provided) reports that cats with coexisting cryptosporidiosis developed earlier, more severe diarrhea after T. foetus inoculation and suggests that coinfection was associated with T. foetus proliferation. However, it identifies the coinfecting organism only as Cryptosporidium spp., not C. parvum, and presents the proliferation finding as suggestive rather than established potentiation. (LLM, conf=0.87)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Findingown data

    The remaining 3 cats had negative results for Giardia spp a few days after treatment, then resumed shedding large numbers of cysts.

    “The remaining 3 cats had negative results for Giardia spp a few days after treatment, then resumed shedding large numbers of cysts.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    All 8 C parvum-infected cats had positive results for Giardia cysts in 5 or 6 fecal samples collected from 1 to 6 weeks prior to treatment, and these cats were considered chronically infected.

    “All 8 C parvum-infected cats had positive results for Giardia cysts in 5 or 6 fecal samples that were collected from 1 to 6 weeks prior to treatment; therefore, these cats were considered chronically infected.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The 8 untreated control-group cats had Giardia spp positive results and C parvum negative results throughout the fecal sample collection period.

    “The 8 untreated control-group cats had Giardia spp positive results and C parvum negative results throughout the fecal sample collection period.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data

    This cat had positive results for C parvum throughout the duration of the study.

    “This cat had positive results for C parvum throughout the duration of the study.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    After 5 days of treatment with fenbendazole, 4 of the 8 treatment-group cats had negative results for Giardia spp and continued to have negative results for the remainder of the study.

    “After 5 days of treatment with fenbendazole, 4 of the 8 treatment-group cats had negative results for Giardia spp and continued to have negative results for the remainder of the study.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    These 4 cats had consistently positive fecal results for C parvum oocysts prior to fenbendazole treatment and consistently negative results after treatment.

    “These 4 cats had consistently positive fecal results for C parvum oocysts prior to fenbendazole treatment and consistently negative results after treatment.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    These 3 cats that transiently had negative results for Giardia spp had negative results for C parvum oocysts for a few days after treatment with fenbendazole, then resumed shedding greater numbers of C parvum oocysts, as they did with the Giardia cysts.

    “These 3 cats that transiently had negative results for Giardia spp had negative results for C parvum oocysts for a few days after treatment with fenbendazole, then resumed shedding greater numbers of C parvum oocysts, as they did with the Giardia cysts.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    In this study, administration of fenbendazole (50 mg/kg, PO, q 24 h) for 5 days lessened Giardia cyst shedding transiently, compared with untreated control-group cats, but only 4 of the 8 treatment-group cats had negative results for Giardia spp at the end of the 3-week study period.

    “In our study, administration of fenbendazole (50 mg/kg, PO, q 24 h) for 5 days lessened Giardia cyst shedding transiently, compared with untreated control-group cats, but only 4 of the 8 treatment-group cats had negative results for Giardia spp at the end of the 3-week study period.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    Benzimidazole anthelminthics inhibit microtubule assembly in helminths and are thought to have the same effect in Giardia spp.

    “Benzimidazole anthelminthics inhibit microtubule assembly in helminths and are thought to have the same effect in Giardia spp.13”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [13] 13. Katiyar SK, Gordon VR, McLaughlin GL, et al. Antiprotozoal activities of benzimidazoles and correlations with β- tubulin sequence. Antimicrob Agents Chemother 1994;38:2086-2090. source

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductnone given

    Control-group cats were infected for a similar period as the treatment-group cats, but they were not treated with fenbendazole.

    “Control-group cats were infected for a similar period as the treatment-group cats, but they were not treated with fenbendazole.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Interpretationreasoning

    It is possible that the infections were not actually eliminated in the cats in this study but that oocyst and cyst numbers were just suppressed to below detectable limits of the assay.

    “Thus, it is also possible that the infections were not actually eliminated in the cats in our study but that oocyst and cyst numbers were just suppressed to below detectable limits of the assay.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The detection limits of the direct immunofluorescence test are the same in cat feces as in human feces.

  • May combine two claims.

    Premisecitation

    When used with human feces, the detection limits of the direct immunofluorescence test used in this study are 100 C parvum oocysts/mL of feces and 100 Giardia cysts/mL of feces.

    “When used with human feces, the detection limits of the direct immunofluorescence test used in our study are 100 C parvum oocysts/mL of feces and 100 Giardia cysts/mL of feces.e”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites e

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    One genotype specific to cats has been isolated.

    “One genotype specific to cats has been isolated.18”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [18] 18. Thompson RCA. Giardiasis as a re-emerging infectious dis- ease and its zoonotic potential. Int J Parasitol 2000;30:1259-1267. source

  • Classified as probably not a substantial claim.

    Premisecitation

    Over 100 compounds have been assessed for the treatment of C parvum in vitro, none of which were found to be universally effective.

    “Over 100 compounds have been assessed for the treatment of C parvum in vitro, none of which were found to be universally effective.19”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [19] 19. Farthing MJG. Clinical aspects of human cryptosporidiosis. Contrib Microbiol 2000;6:50-74. source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Although benzimidazoles are widely used by veterinary practitioners for the treatment of giardiasis in cats, there has only been 1 published study in which albendazole treatment was reportedly ineffective.

    “Although benzimidazoles are widely used by veterinary practitioners for the treatment of giardiasis in cats, there has only been 1 published study in which albendazole treatment was reportedly ineffective.a”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites a

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationown data

    Our findings suggest that administration of fenbendazole will be effective for lessening Giardia cyst shedding and eliminating Giardia infection in some cats.

    “Our findings suggest that administration of fenbendazole will be effective for lessening Giardia cyst shedding and eliminating Giardia infection in some cats.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The Giardia strain used, a human isolate, is representative of Giardia strains that naturally infect cats, so that treatment results can be generalized to feline giardiasis.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given

    The Giardia strain used in this study was initially isolated from a human.

    “The Giardia strain used in our study was initially isolated from a human.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Metronidazole is another drug frequently used but was less effective than albendazole in treating giardiasis in vitro.

    “Metronidazole is another drug frequently used but was less effective than albendazole in treating giardiasis in vitro.23”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [23] 23. Meloni BP, Thompson RCA, Reynoldson JA, et al. Albendazole: a more effective antigiardial agent in vitro than metron- idazole or tinidazole. Trans R Soc Trop Med Hyg 1990;84:375-379. source
20 of 20

  • The authors state this as an assumption.

    Fenbendazole has not been evaluated for the treatment of Giardia infection in cats.

    “To our knowledge, fenbendazole has not been evaluated for the treatment of Giardia infection in cats.”

  • The paper relies on this without support.

    The detection limits of the direct immunofluorescence test are the same in cat feces as in human feces.

    “When used with human feces, the detection limits of the direct immunofluorescence test used in our study are 100 C parvum oocysts/mL of feces and 100 Giardia cysts/mL of feces.e”

  • The paper relies on this without support.

    The Giardia strain used, a human isolate, is representative of Giardia strains that naturally infect cats, so that treatment results can be generalized to feline giardiasis.

    “The Giardia strain used in our study was initially isolated from a human.”
3 of 3

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • A count of 250 cysts falls in two score categories

    Minor

    The scoring rules assign 250 cysts per slide to both score 1 and score 2, so that count has no unique score.

1 of 1

Cites

Flagged first, then by citations

Research works printed but not linked: 5

  1. Kirkpatrick CE, 1984, Am J Vet Res, 45, 2182
  2. Brightman AH, 1976, J Am Anim Hosp Assoc, 12, 492
  3. Kirkpatrick CE, 1985, J Am Vet Med Assoc, 187, 161
  4. Youssef MY, 1996, J Egypt Soc Parasitol, 26, 543
  5. Zimmer JF, 1987, Cornell Vet, 77, 383

Cited by

Sorted by citations

Related

Authors
Keith, C. L., Radecki, S. V., & Lappin, M. R.
Affiliations
Colorado State University (US)
ORCID
Lappin, Michael R.
Venue
American Journal of Veterinary Research
Publisher
American Veterinary Medical Association (AVMA)
Published
2003-08-01
Volume
64
Issue
8
Pages
1027-1029
ISSN
0002-9645 (ISSN-L)
DOI
10.2460/ajvr.2003.64.1027
OpenAlex
W2031691174
Semantic Scholar
0ce8f26b89278a2dd6b68ce1cfad1bfb4a36adb9
Cited by
37
References
24
Citations by year
2025: 2 · 2024: 1 · 2021: 5 · 2020: 2 · 2016: 1 · 2015: 1 · 2014: 1 · 2013: 3 · 2012: 2
FWCI
2.24
Type
journal article
Language
en
Open access
Locations
  • American Journal of Veterinary Research (publishedVersion)
  • PubMed (publishedVersion)
Topics
  • Life Sciences › Immunology and Microbiology › Parasitology › Parasitic Infections and Diagnostics
  • Health Sciences › Veterinary › Small Animals › Helminth infection and control
  • Health Sciences › Veterinary › Small Animals › Veterinary medicine and infectious diseases
Keywords
fenbendazole, Giardia lamblia, Cryptosporidium parvum, cryptosporidiosis, anthelmintic efficacy, cats
MeSH terms
Animals, Antiprotozoal Agents, Cat Diseases, Cats, Cryptosporidiosis, Feces, Fenbendazole, Giardiasis, Cryptosporidium parvum

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Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-11.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-11.

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