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Getting the balance right - Responsible use of small animal parasiticides

14 Dec 2020 | Justine Shotton


Zoo vet and BVA Junior Vice President Justine Shotton considers how the profession can help to mitigate the ecological impact of parasiticides whilst protecting animal health and welfare and public health.

Getting the balance right - Responsible use of small animal parasiticides Image

We are now all very familiar with the serious risks of indiscriminate use of antimicrobials and parasiticides regarding the development of resistance. However, there are also wider environmental concerns with the use of these products. A recent study, published by a team at the University of Sussex, has highlighted the fact that agents in many common topical ectoparasiticides (including fipronil and imidocloprid) have been found to be present at dangerous concentrations in many UK rivers ( The potential impact of these agents on aquatic ecosystems is high, and it highlights the need for our profession to move towards a more responsible, risk-based approach to using these products. 

We have a duty as vets to responsibly recommend and prescribe appropriate endo- and ecto-parasiticides to our clients, not only to protect animal health and welfare but also to ensure we are protecting public health from zoonotic parasites. Practices also often derive significant income from the sales of these products. So, what may be some ways that you can practically help to mitigate the ecological impacts of these agents, while still optimising animal and human health? 

Adopting a risk-assessment based approach to each patient would be a huge step in the right direction. This would involve moving away from blanket prophylactic treatment, and instead considering that individual animal’s circumstances. What is their parasite risk, based on their lifestyle, their environment, the local prevalence of the parasites, their geographical location and the season? What products would be most appropriate for protection, and which may have the least ecotoxicity but still be efficacious and safe? 

Regarding endoparasites, moving more towards regular faecal screening as is done in the livestock and equine sector would not only provide practices with alternative income, but would also allow targeted treatment to the parasites they harbour, avoiding polypharmacy and a ‘one treatment for all parasites’ approach. This would not only have the potential to reduce environmental impact but would also help to reduce the development of parasite resistance to these products. The European Scientific Counsel Companion Animal Parasites is a useful resource for expert, evidence-based guidelines on the use of parasiticides in small animals, and a good place to look for more information.

Another suggestion from Rosemary Perkins, a former small animal vet and co-author of the recent study, would be to recommend, where possible, oral formulations of products, and to move away from topical products. Oral products tend to be excreted in the faeces, and at least for dogs, this means the contaminated waste is easier to collect and dispose of. While datasheets of some topical products recommend not allowing pets access to water for a few days after treatment, often this information isn’t always passed on to our clients. It is our professional duty to remind clients to follow datasheet guidelines, not only to ensure efficacy but also to help to reduce ecotoxicity. 

There is the possibility that as these issues become more acute, organisations such as the VMD may reclassify these types of pharmaceuticals to veterinary-prescription only, which would help ensure veterinary surgeons are empowered not only to continue gaining income from these sales, but also giving them an opportunity for increased client education around parasite treatments, allow more client and patient engagement and contact time, and helping to promote these vital environmental issues through judicious use.

There are real and serious consequences of not addressing our current blanket use of parasiticides, including watercourse ecosystem declines and global invertebrate declines. Our profession cares deeply about environmental issues, and a number of working groups, including the RCVS’s Environment and Sustainability Working Party, with members including  BVA and Vet Sustain, have been recently set up to work on formulating the best advice for members of our profession, equipping them with evidence-based tools to help inform their prescribing. 

At Marwell Zoo where I work in my day job, we work closely with our Conservation Team to try to assess the local environmental impact of the pharmaceutical agents we use, and we aim to come up with strategies to reduce the likelihood of ecological impact. We rarely use topical applications (not least because we often cannot get physically close enough to our animals to safely apply them!), we always use endo-parasiticides based on faecal egg counts and ensure post-treatment reductions are achieved, and we consider whether there are husbandry and environmental strategies to avoid the need for pharmacological treatments. These strategies include: reducing stocking densities; mixed-species grazing exhibits; providing con-specifics for mutual grooming or providing scratching posts to remove large ecto-parasites like ticks; increased exposure to UV and improved nutrition to maximise skin health; and improved hygiene. We also aim to offer animals access to grazing or browsing plant selections which may either improve resistance to parasites or provide some natural pharmaceutical properties against some parasites. While there is limited peer-reviewed evidence of the latter currently available, anecdotally this is a strategy that many zoologists believe that animals may naturally exploit in the wild. 

Vet Sustain are hosting a webinar on Wednesday 16 December at 8pm on this topic led by the authors of this recent study. This is free to attend, so if you want to find out more and join the discussion, sign up on The Webinar Vet website. Vet Sustain and SPVS are also running a virtual conference in January on sustainability in our profession, so get involved with that too.

BVA’s #TeamGreenVet page has some fantastic resources around sustainability, including the upcoming BVA and Vet Sustain’s sustainability practice checklist, which fantastic resource to start improving all aspects of your practice’s sustainability. 

While the recent study focused on agents in watercourses which have most likely come from the use of small animal ectoparasite topical preparations, it is important to remember that all pharmaceuticals given to animals have the potential for environmental contamination. This could include farm-animal ivermectin type pour-ons (which have extremely high levels of toxicity to aquatic life), but also antibiotic use, the metabolites of which may have the potential to affect soil microbiomes, for example. 

Veterinarians across the spectrum of small animal, equine, livestock and zoo fields, all have a shared responsibility to ensure we protect the animals under our care, safeguard public health, and still promote and conserve our environment. At  BVA, we are extremely passionate about helping our members and the wider profession to achieve these goals. 


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