Plea for caution as new report warns of parasiticide pollution threat

Vets need to be “a lot more cautious” about the use of flea and tick treatments on companion animals because of their potential environmental impact, scientists have warned.

Newly published research, led by academics from Imperial College London, has revealed that parasiticide chemicals are being found in urban waterways at levels that can be toxic to aquatic species.

Concern about the issue has been growing within the veterinary profession for some time and the researchers themselves acknowledge that significantly more data is required.

But Andrew Prentis, a retired vet and one of the co-authors of the briefing paper, said its findings should serve as “a wake-up call” to the sector.

Guardians

Dr Prentis acknowledged he would have contributed to the problem himself during a near 40-year career in practice.

But he added: “We appoint ourselves as guardians of the animal kingdom, as a veterinary profession, and we need to be very careful that we’re not doing damage.

“We need to progress with a great deal more caution than we have so far. We need a lot more information, a lot more data and we need to be a lot more cautious in what we’re doing.”

Banning usage

Dr Prentis also suggested that a ban on preventive usage may be a sensible measure, but stressed that, while other countries had taken that step, there was insufficient evidence to justify it here.

The briefing paper highlights Environment Agency monitoring of 20 English rivers between 2016-18, which found that one of the most commonly used ingredients in parasiticides, imidacloprid, was present in two-thirds of samples, with seven sites exceeding chronic toxicity levels.

Where detected, 52% of cases were deemed to have a moderate to high risk of impact on freshwater species, although the authors argued that may be a conservative estimate.

Following an EU ban on outdoor use five years ago, veterinary parasiticides are thought to be the most common source of imidacloprid in the UK, with 138 products containing the chemical authorised for use.

Negative effects

The researchers also warned that little was known about the concentrations or effects of other, more recently introduced parasiticides; although, it was “only logical” to expect them to have strong negative effects.

The paper sets out 10 separate policy recommendations, including a review of requirements for a pre-approval environmental impact assessment, plus an immediate re-examination of products when use of their active ingredients is banned in other areas.

It also calls for measures including offering incentives to pet owners to return products they do not use for safer disposal, consideration of whether approved parasiticides should only be available on prescription, and reduction of prescriptions to meet animals’ real treatment needs, rather than those that are perceived.

Data needed

Although the latter is among the areas where the researchers said more data is needed, Dr Prentis – a member of Vet Sustain and a Visiting Fellow in Imperial College London’s Grantham Institute, highlighted VetCompass figures that suggest only 2% of dogs and 1.5% of cats actually have fleas.

He suggested there was “a real mismatch” between the volume of treatment being administered and the actual level of risk, arguing that the focus ought to be on levels of sickness, rather than levels of infection.

He said: “In the same way that we only take antibiotics when we’re ill – not every month – we may need to apply the same principle to parasite treatments for our pets.”

Financial implications

The report also highlighted the potential financial implications of a change in approach, pointing out that parasiticide sales “represent a significant revenue stream for many veterinary teams”.

But the research team believes encouragement can be drawn from the progress made in recent years to reduce levels of antimicrobial usage amid the health threats posed by resistance.

Tilly Collins, from the university’s Centre for Environmental Policy, said: “We want vets to be doing evidence-based prescribing. We want them to be responsible and we want to provide them with the real-world data that allows them to advise their customers.”

Call echoed

The call for further research has been echoed by the BVA, which published a five-point plan on the subject in conjunction with the BSAVA and the British Veterinary Zoological Society last September. The material was the first resource to be released after the three bodies set out a joint policy position on the issue in 2021, and more materials are set to follow.

BVA senior vice-president Justine Shotton said: “Parasiticide treatments do an important job in preventing, treating, and protecting both animals and humans from illnesses and conditions linked to parasites.

“However, it is important to consider the impact these products may have on the environment. There are still many knowledge gaps surrounding parasiticide products, so this research – although shocking – by the Imperial College is welcome. This is a true one health problem, with veterinary professionals needing to balance animal health, human health and the health of the wider ecosystem.

“Pet owners should always speak to their vets, who will talk through different parasiticide options to find the best solution to prevent and treat parasites as needed for their pet.”

The publication of the briefing paper also comes in the final stages of the public consultation on proposed reforms of the Veterinary Medicines Regulations, which is due to close on Friday 31 March.