Can garlic prevent, repel or kill fleas that infest dogs?

PICO question 
In dogs, is oral or topical administration of garlic, compared to no treatment, efficacious at preventing or reducing parasitism by fleas? 
  
Clinical bottom line 
Category of research question 
Treatment 
The number and type of study designs reviewed 
Zero 
Strength of evidence 
Critical appraisal of the selected papers meeting the inclusion criteria collectively provide zero evidence in terms of their experimental design and implementation 
Outcomes reported 
The outcomes reported were none 
Conclusion 
It is concluded that there is a lack of peer-reviewed scientific in vivo evidence to address the PICO 
  
How to apply this evidence in practice 
The application of evidence into practice should take into account multiple factors, not limited to: individual clinical expertise, patient’s circumstances and owners’ values, country, location or clinic where you work, the individual case in front of you, the availability of therapies and resources. 
Knowledge Summaries are a resource to help reinforce or inform decision-making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care. 
  



Treatment
The number and type of study designs reviewed

Strength of evidence
Critical appraisal of the selected papers meeting the inclusion criteria collectively provide zero evidence in terms of their experimental design and implementation

Outcomes reported
The outcomes reported were none

Conclusion
It is concluded that there is a lack of peer-reviewed scientific in vivo evidence to address the PICO How to apply this evidence in practice The application of evidence into practice should take into account multiple factors, not limited to: individual clinical expertise, patient's circumstances and owners' values, country, location or clinic where you work, the individual case in front of you, the availability of therapies and resources.
Knowledge Summaries are a resource to help reinforce or inform decision-making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.

Clinical Scenario
A veterinary nurse is reading through the ectoparasiticide advice being given in a Facebook group that encourages a 'natural' (non-conventional medicine) approach to preventative medicine in dogs. She notices that garlic is being recommended quite frequently by some pet owners as an alternative to a conventional ectoparasiticide for preventing or treating flea infestation on dogs and wonders what the evidence base is for this recommendation.

The evidence
No peer-reviewed scientific papers were identified that addressed the PICO. Widening the inclusion criteria to include garlic applied environmentally (the same search strategy was retained) to address extra dog environmental infestation, or case studies based on oral, topical or environmental application of garlic also yielded no results.

Summary of the evidence
There was no peer-reviewed evidence that met the inclusion criteria to summarise.

Appraisal, application and reflection
No in vivo studies that examine the efficacy of garlic at preventing, killing or repelling any stage of the flea life cycle in dogs were identified from the search strategy applied, and therefore no papers met the inclusion criteria for this Knowledge Summary. One in vitro study (Renapurkar & Deshmukh, 1984) was identified which demonstrated that environmental application (on to filter paper) of garlic extract in a hexane solvent was efficacious with the LC50% (the concentrate that kills 50% of the animals tested on) concentration of garlic extracts similar to that for various organochlorine and organophosphorus (Dieldrin; Malathion; Fenthion; Dichlorodiphenyltrichloroethane). However, external validity (e.g. oral or topical application of garlic to the dog with, or at risk of, flea parasitism) should not be inferred from these findings due to the numerous differences between laboratory and clinical application.
There is some evidence of in vitro efficacy of garlic application across parasitised species and ectoparasites from various phyla, which suggests that it may have its place as a plant-based ectoparasiticide for the ethnoveterinary based treatment of some species. In two cattle-based studies (both abstract only as the full text was in Spanish), oral supplementation with garlic ( . This cross phyla efficacy may suggest a tentative basis for clinical research to investigate the efficacy of garlic as a plant-based ectoparasiticide to prevent, repel or kill fleas in the domestic dog. However, until garlic has been shown to be efficacious against fleas in dogs (and at levels non-toxic to the canine) the veterinary professional cannot make assumptions of external validity based on the studies cited, and clients should be recommended to use instead an ectoparasiticide that has been demonstrated to be so.