The Big Flea Project, sponsored by MSD Animal Health (the maker of Bravecto), has published a study which found significantly more fleas on cats and dogs in Wales, and on animals which had been treated with fipronil as opposed to other antiparasiticides.

For the study, which was conducted in 2018 and published this year in Medical and Veterinary Entomology1, practices from around the UK sent in combings from 812 cats and 662 dogs for analysis. 

28% of the cats and 14% of the dogs were found to be carrying fleas, with cats from central Wales and the Welsh Borders being more than twice as likely to have fleas than elsewhere in the country. Likewise, dogs from North Wales, the North Wales borders, South Wales and South West England were between 3 and 4.5 times as likely to have fleas as elsewhere.

Of the cats treated with fipronil, 62% (n=57) were still found to be carrying fleas despite treatment. Of the dogs, 44% (n=49) of those treated with fipronil were still carrying fleas. By contrast, 4.1% of cats and 1.4% of dogs treated with fluralaner (Bravecto) were found to have fleas (the lowest of any treatment).  

Professor Richard Wall, Veterinary Entomologist at the University of Bristol said: "There is a clear need for greater owner education about the importance of flea treatment and a better understanding of the efficacy of different flea and tick prevention products.

"It is critical for vets to not only recommend the best product for a pet’s needs but to also give a better understanding of the effectiveness and correct application of the different treatments."


  1. Cooper et al. (2020). Fleas infesting cats and dogs in Great Britain; spatial distribution of infestation risk and its relation to treatment. Medical and Veterinary Entomology, doi: 10.1111/mve.12462

Photo:  Professor Richard Wall, University of Bristol

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