There are emerging concerns that parasiticide use in small animal veterinary medicine is contributing to environmental contamination with pesticide compounds
Over the last few years, there have been emerging concerns that parasiticide use in small animal veterinary medicine is contributing to environmental contamination with pesticide compounds. The most studied of these compounds are fipronil and imidacloprid, agents which are highly toxic to invertebrates and found in topical spot-on flea treatments for our pets (Kindemba, 2009; Perkins et al, 2021) and which also show toxicity to non-target taxa (Gibbons et al, 2014). The concern is that as these products build up in our rivers and waterways, the direct and indirect impacts on invertebrates, as well as other non-target species, including humans, could be devastating and irreversible.
The effect of drugs and medicines on the environment
More and more evidence is accumulating around the effects of medicines and drugs in our environment – so these products are by no means the only cause for concern. Prozac metabolites in the environment contaminated by human sewage may alter starling physiology and behaviour (Bean et al, 2014) and illicit drugs such as cocaine may be affecting aquatic organisms such as eels (Capaldo et al, 2018) and shrimps (Miller et al, 2019). The effects of drugs and their metabolites in the environment are not yet fully understood but could include lethal and sub-lethal effects in many non-target species, including changes to behaviour and reproduction. Pesticides such as neonicotinoids are compounds of particular concern globally, due to their high toxicity to invertebrates and implication in declines in insect populations, leading to many bans and restrictions of their use in agriculture. For example, the EU banned outdoor use of neonicotinoids in 2018 to protect pollinators such as bees. However, with an increasing pet population, contamination from parasiticide products must also be carefully considered.
As the veterinary professions, we have long been advocating for regular prophylactic treatment for pets to avoid endo- and ecto-parasites, both to prevent health and welfare issues in pets but also to protect the pet-owning and wider public from rare but genuine zoonotic disease risks. However, as evidence-based professions, we must continuously react to new and emerging evidence, and adapt to the potentially extremely severe implications of widespread contamination of these products. Therefore, we need to move away from the blanket preventative treatment we have long recommended, towards a more case-by-case, risk-based approach for each patient, carefully balancing not only the immediate and future needs of the animal under our care, but also the health of the public and the health of the ecosystems which we all live in and depend upon.
Risk-based and balanced approach
Despite some research suggesting more optimism around the impacts of veterinary medicinal products (Anthe et al, 2020), recent evidence (Perkins et al, 2024) suggests common activities such as hand-washing and bathing of dogs and their beds are routes that spot-on parasiticides can enter UK waterways, meaning mitigations such as preventing dogs from swimming in rivers following the application of these products is unlikely to be sufficient to reduce harmful impacts. UK Pet Food population data (UK Pet Food, 2024) estimates there are 13.5 million pet dogs in the UK, with 36% of households owning a dog, and 12.5 million pet cats – making up 29% of all households owning a cat – meaning the amounts of parasiticides being used is significant.
As well as years of advice from the vet profession around regular prophylactic treatment, many parasiticides are also available over-the-counter without a veterinary prescription. A further complexity when we consider what the best course of action is to protect our planet as well as our pets, is that we don't know ‘how bad’ the alternatives might be. While there is evidence that topical spot-on ingredients may be extremely harmful to aquatic life, we don't yet have data comparing the impacts of metabolites of oral products that are faecally excreted, for example. Therefore, while we must take a risk-based, balanced approach to prescribing topical spot-ons and other parasiticides, we should be mindful to also be educating owners to poopick, for example, and not leave their pet's faeces in the environment.
Zoonotic risks
A common question asked when we consider responsible use of pet parasiticides is why we don't do what our farm and equine colleagues have been doing for years, testing faecal samples and only treating where appropriate, due to serious concerns around anthelmintic resistance developing. Again, the answer is complex, comprising of a combination of differing drivers for change (there is currently very limited evidence suggesting any resistance in small animal parasiticides), differing parasite life-cycles (for example intermittent shedding of eggs making diagnosis difficult), lack of accessible tests with high sensitivity and specificity, depending on the parasite, and possibly most importantly, the presence of zoonotic parasites in our small animal companions. While zoonotic disease from pet parasites is rare, it is an ethical conundrum to balance these real risks, particularly in children and immunocompromised individuals, and determine whether any shedding of potentially zoonotic parasites should be tolerated.
Resources to help
Given all the risks, not only to the planet and people but also to our pets – from in some cases debilitating welfare-compromising conditions such as flea allergic dermatitis or lungworm – then what should our professions do to balance all of these challenges? The British Veterinary Association (BVA), British Small Animal Veterinary Association (BSAVA) and British Veterinary Zoological Society (BVZS) policy position on the Responsible use of parasiticides for cats and dogs (BVA, 2021) suggests some ways forward and BVA offers a suite of resources to help (see https://www.bva.co.uk/take-action/our-policies/responsi-ble-use-of-parasiticides-for-cats-and-dogs/). With so many unknowns, and so little definitive evidence providing a clear steer on best practice, the advice as it stands is to adopt a case-by-case, risk-based approach to prescribing and using these products for pets. Veterinary professionals must understand the risks, not only to pets but also people and the planet, and work with clients to prevent and check for parasites in a risk-based way. They should take into account the individual lifestyle factors of each patient and come up with a plan to best protect that pet while also considering salient zoonotic risks and likely environmental risks.
The role of the veterinary professional
Inevitably, this process will take time and effort, and recognising in your teams that this is a challenge we must adapt to is key. It will also take time to talk through risks with your clients – and using nurse clinics and bespoke ‘parasite planning’ consults would be a good way to approach this. Talking through lifestyle factors, such as whether the pet lives inside or out, whether they are regularly groomed or swim, whether they're on a raw diet, knowing local risks such as lungworm or whether the pet walks in tick-dense habitats or travels internationally, as well as what people share the house with these pets, are all important to help inform which products to use and when. Using narrow-spectrum products where possible should help to target treatment to the parasites of concern, and avoiding topical spot-ons for pets that regularly swim or are bathed at the groomers seems a sensible approach to help reduce ecosystem impacts as far as we currently understand them. Proper administration and disposal of products should be demonstrated and talked through with your clients, and you should keep accurate records of decisions made, treatments given and outcomes, including reporting any suspected treatment failures or adverse reactions. Advising your clients to pick up their pet's poo and dispose of it in waste is important, as is following the datasheets regarding appropriate application.
Green pet health plans
Another exciting area to develop as a practice is the use of more green pet health plans. Moving away from health plans that supply a year's worth of parasiticide products and an occasional health check, to a structured preventative healthcare plan tailored to that pet, is a fantastic way to bond clients, increase practice income, and move away from ‘blanket’ prophylactic parasite treatment. These plans could include a bespoke parasite consultation, certain parasite tests, a nutrition consult, a dental health consult, and a consultation around wider green pet ownership issues such as toys and activities with pets, for example.
Conclusions
Our professions have important responsibilities towards the animals under our care, our clients and the wider public, and the ecosystems which are essential for human and animal health and welfare, both now and into the future. Balancing the ‘right’ thing to do with limited data and evidence and facing challenging ethical questions around complex One Health topics such as this, is something that I believe our professions are particularly good at. We often never have all the answers, but we are experienced in making a pragmatic best guess, considering all of the factors and consequences at stake. Given the high consequences at stake in the issue around the impacts of parasiticides, it is our duty as veterinary professionals to embrace these challenges, have the difficult conversations with our clients, and re-think our approach to preventative health.