Written by Elsbeth Leighton, Coalface to Wildspace Project Assistant
As a nation, the UK has a lot of pets, so much so that we are often labelled as a “nation of animal lovers”. Over half of us have pets, which includes 12 million dogs, 11 million cats and another few millions small animals such as rabbits and hamsters (Kantar/Soulor Consulting, 2023). Being responsible and caring pet owners, we want to do what’s best for our animals and follow vet advice about how to keep them healthy and happy. For many of us, that now includes a regular flea and worm treatment for our cats and dogs to prevent any nasty infestations.
This treating of healthy pets with regular doses of parasiticides, i.e. medicines to treat fleas, worms and other parasite infections, as a way to prevent rather than cure infestations is called prophylactic treatment as opposed to reactive treatment. This approach has the benefit that, since it can prevent infestations before they start, it also has a good chance of preventing the unpleasant complications that can sometimes arise from pet parasite infections, such as such as flea allergy dermatitis or disease spread (Murphy and Wright, 2020). This seems quite sensible, but could this approach be harming the environment and our wildlife?
It’s well known by now that pesticides used on crop fields have negative effects on wildlife and the environment (e.g. Sánchez-Bayo, 2021). Neonicotinoids, in particular, are now notorious for their deadly impact on insects and bees in particular, which earned them a ban from use in agriculture by the European Union in 2018 (European Commission, 2023). However, what many of us may not know is that many of those same pesticides that can no longer be used in agriculture are still allowed to be used in other settings, including in pet parasiticides. This decision has been justified by the reasoning that so little of these pesticides is used per pet and even less will reach the outside environment, so the threat to the environment must be very small and not worth worrying about.
However, a recent review of the research around pet parasiticides by Preston-Allen and their team from the Grantham Institute, shows that this assumption is incorrect and our fleaing and worming treatments present a real danger to wildlife, and freshwater habitats in particular. They point out that imidacloprid, one of the most popular pet parasiticides as well as a neonicotinoid banned for agricultural use, was found at toxic levels in two thirds UK rivers surveyed in a recent study (Perkins et al, 2021). Given that these chemicals are no longer used in agriculture, the most likely source is from our pets. Research looking into how pet parasiticides might get into our freshwater habitats indicated that wastewater, i.e from our drains and our washing machines, is the main route, but that shedding of pet hair, pet urine and outdoor swimming are also causes (Preston-Allen et al, 2023, Diepens et al, 2023).
Once they have made it into the environment and into our ponds, lakes and rivers, these chemicals can have devastating impacts on wildlife. These parasiticides are designed to kill invertebrates and this includes our freshwater insects. The research shows that they are deadly to many species of freshwater invertebrates, and they can also have serious negative effects on other animals, including fish, birds and mammals (Preston-Allen et al, 2023). Not all of these animals die from the parasiticides, but they may be impacted in other ways. For example, one study showed that fish with pet parasiticides in their water swim slower and lower in the water, which makes it harder for them to forage for food and easier for predators to catch them (Domingues et al, 2016). Effects like these can impact on the relationships between species and damage the overall health of our ecosystems.
Not only does the current prophylactic approach to pet parasiticides pose a threat to the environment and our wildlife, but there are also concerns it will lead to parasites developing resistance to these drugs (Nind and Mosedale, 2022). This is analogous to the issue of antibiotic resistance, where overuse of some drugs leads to the diseases that we want to target becoming resistant to antibiotics due to overexposure, making it harder to treat these infections (e.g. GLASS Report, 2022). If we keep overusing these pet parasiticides, it is highly likely that these parasites we are aiming to prevent will become resistant and treating infestations in the future will be much more challenging.
So, what can we as pet owners do?
The key recommendation from the researchers is to start treating these issues reactively instead of prophylactically if you can. This means checking our pets regularly for any signs they may have fleas or worms and seeking vet treatment when it arises, instead of regularly dosing healthy pets with parasiticides. This might not be the ideal solution for everyone as the risks from infestations are higher for some people, such as those with pets that are more vulnerable to complications from fleas or owners who are immunocompromised. So, we should all individually evaluate the level of risk we and our pets face to determine the best approach for us that balances our needs against the environmental impact of these parasiticides.
As well as aiming to limit the amount of parasiticide treatments we use through a return to reactive treatment, we can aim to reduce the amount of these chemicals that leak into the environment when we do use them. This might mean keeping your cat inside for a few days after applying a spot-on treatment, or not washing your pets bedding as frequently when your pets have been treated, as these are both ways parasiticides can make their way into the environment (Preston-Allen et al, 2023). Another key step we should all try to take is being careful to keep our dogs out of streams and other water bodies when they’ve been treated for parasites recently. It is best to try to avoid letting dogs in wild water bodies in general, as they can stir up and disturb the organisms and plants living there, but especially when they have just been treated for parasiticides as they can wash off into the water (froglife, 2022).
References
Diepens, N.J., Belgers, D., Buijse, L., Roessink, I., (2023) Pet dogs transfer veterinary medicines to the environment. Science of The Total Environment. https://doi.org/10.1016/j.scitotenv.2022.159550.
Domingues, I., Oliveira, R., Soares, Amorim, M.V.M., et al. (2016). Effects of ivermectin on Danio rerio: a multiple endpoint approach: behaviour, weight and subcellular markers. Ecotoxicology. https://doi.org/10.1007/s10646-015-1607-5.
European Commission, (2023). Neonicitinoids, https://food.ec.europa.eu/plants/pesticides/approval-active-substances/renewal-approval/neonicotinoids_en, accessed 15/12/2023
Froglife, (2022). #pawsagainstponds Campaign, https://www.froglife.org/2022/03/22/pawsagainstponds-campaign/, accessed 15/12/2023
Global antimicrobial resistance and use surveillance system (GLASS) report, (2022). Geneva: World Health Organization. Licence: CC BY-NC-SA 3.0 IGO.
Kantar/Soulor Consulting, (2023). online survey with 8,901 respondents, https://www.ukpetfood.org/information-centre/statistics/uk-pet-population.html
Murphy, D, Wright, I., (2020). Value of using preventive pet parasiticides. The Veterinary Record. Feb 29;186(8):252. doi: 10.1136/vr.m727.
Nind, F., Mosedale, P., (2022). Antiparasitic Resistance. BSAVA Guide To The Use Of Veterinary Medicines. https://www.bsavalibrary.com/content/chapter/10.22233/9781905319862.chap20?crawler=true&mimetype=application/pdf
Perkins, R., Whitehead, M., Civil, W., Goulson, D., (2021). Potential role of veterinary flea products in widespread pesticide contamination of English rivers. Science of The Total Environment. https://doi.org/10.1016/j.scitotenv.2020.143560.
Preston-Allen, R.G.G., Albini, D., Barron, L., Collins, T., Dumbrell, A., Duncalf-Youngson, H., Jackson, M., Johnson, A., Perkins, R., Prentis, A., Spurgeon, D., Stasik, N., Wells, C. and Woodward, G., (2023). Are urban areas hotspots for pollution from pet parasiticides? Grantham Institute Briefing. note #15. Doi: https://doi.org/10.25561/102699
Sánchez-Bayo F., (2021). Indirect Effect of Pesticides on Insects and Other Arthropods. Toxics. Jul 30;9(8):177. doi: 10.3390/toxics9080177.