Parasiticides are substances used to treat and prevent parasitic infections in animals, including those caused by fleas, ticks, mites and worms. There are approximately 100 different parasites that can affect dogs and cats, with the majority belonging to a group called nematodes. Parasiticides can be life saving for pets and people.
Over the last 10–20 years, pharmaceutical products have shaped better practice and made parasite control a great success. Responsible use of parasiticides is essential to ensure the health and safety of pet animals, humans and the environment. The One Health initiative says that the health of humans and animals are interconnected, and both depend on the environment.
What can veterinary professionals do to ensure responsible use?
Education of both veterinary professionals and pet owners is key. Veterinary nurses should stay informed by keeping up to date with the latest advances in parasite control and following recommendations from reputable veterinary organisations. Veterinary professionals should also seek advice when needed. ESCCAP UK & Ireland is a useful and responsive resource. Owners should be educated to:
- Administer the product correctly: apply or administer the parasiticide as directed (eg, directly on the skin, orally), and do not use on species or age groups for which it is not intended
- Accurate dosing: use the correct dosage based on the pet's weight and species. They should avoid ‘guessing’ doses
- Follow the label instructions: read and follow the product label instructions carefully, including dosage, application method, frequency and safety precautions.
Parasite control wisdom
A few veterinary professionals have historically argued that all cats and dogs need to be treated against all parasites all of the time. However, blanket treatment like this is inappropriate and individualised treatment plans work better. Regular checks can help with any concerns or problems.
An individualised treatment plan tailored to the pet's specific needs should be based on:
- The health status of the pet
- Factors like species, age, regional risk, household and lifestyle
- Identified risk factors
- Client communication/engagement
- Education.
The benefits of tailoring control include that it is more eco-friendly, owners are more likely to comply when using less product, it is lower cost and it results in less drug exposure for pets.
Proper product selection is needed. It must be an appropriate formulation suitable for the pet's species and the intended use, for example:
- For dogs or cats
- Topical (spot-on, spray, or collar) or oral (tablet)
- Zoonotic or non-zoonotic
- Single or multiple parasites
- Narrow or broad spectrum.
Broad spectrum is needed for many animals at medium-to-high-risk – it can improve compliance and simplify treatment for owners and pets. Narrow spectrum is needed for some animals at low risk, targeted at particular parasites (eg, fleas or mites) and this can be good for the environment and sustainability.
Rotating different classes of parasiticides can reduce the risk of resistance development in parasites. Responsible use of parasiticides is less about reducing the frequency of application than it is rationalising the use of these products.
The issue with worming frequency
Monthly worming prevents shedding of eggs and contamination of the environment, whereas quarterly worming leaves large gaps, allowing worm maturation. Just one worm can lay over 85 000 eggs per day, which can contaminate the environment. It is important to treat pregnant bitches and queens, nursing bitches and queens and puppies and kittens to help prevent transmission and development of patent infection.
In the UK, monthly treatment is needed for Toxocara (a possible exception is indoor cats) and fleas (even indoor cats can be infected by visiting pets, wild animals, people), as these both have animal health and zoonotic implications.
Hany discussed that monthly Toxocara treatment is needed if the pet is a puppy or a kitten, the pet hunts or scavenges, the pet eats unprocessed raw food or has access to carcasses or if children less than 5 years of age or immunosuppressed individuals live in the household.
Quarterly tick treatment is needed if the pet lives in an endemic foci for tick-borne pathogens such as Borrelia, Babesia canis or tick-borne encephalitis, if the pet visits pasture shared by deer or domestic ruminants, bracken, tall grass/undergrowth or animal burrows or if the pet has a history of tick exposure.
Quarterly lungworm treatment is needed if the pet lives in an endemic lungworm area, the pet deliberately consumes slugs or snails, the pet has a previous history of lungworm infection, the pet is a serial grass consumer or is coprophagic, or lungworm is prevalent locally based on regional cases.
Quarterly tapeworm treatment is needed if the pet hunts, the pet eats unprocessed raw food or has access to carcasses, the pet has unmonitored off-lead access to pasture or the pet lives in an Echinococcus granulosus endemic area.
Monitoring and reporting
Check ups are needed to assess the patient's parasite risk and adjust treatment protocols as needed. It is important to monitor for any adverse effects after administration – these should be reported to the Veterinary Medicines Directorate pharmacovigilance service. If parasiticides appear ineffective over time, inform the veterinarian. This could indicate the development of resistance in parasites or a breakdown of parasite control.
How do pharmaceuticals affect the ecosystem?
It is not just parasiticides that affect the ecosystem. Antibiotics, analgesics and psychiatric drugs have all been detected. To avoid environmental contamination with parasiticides, pet owners should be educated on the correct application of the product. Swimming or shampooing the pet should be avoided after topical applications. Applying parasiticides near water bodies or areas where runoff could contaminate groundwater should be avoided, and packaging, unused or expired products should be disposed of responsibly.
Additional measures to prevent environmental contamination with parasites include the bagging and disposal of faeces and cat litter boxes should be cleaned daily and litter double bagged and disposed of in household waste.
ESCCAP UK & Ireland recommend faecal testing alongside worming rather than as a substitute. Testing alone is not efficient as a positive result means it is too late – environmental shedding has already occurred. This is a risk in the case of zoonotic parasites such as Toxocara and some parasites can cause illness before producing the diagnostic stage (eg Angiostrongylus). Sensitivity and specificity are also not optimal, and parasite excretion or shedding can be intermittent and irregular and does not necessarily correlate with the parasite burden in the body.
Conclusions
The use of parasiticides serve a vital function because they protect the health and welfare of pets and people. There are increasing calls for responsible use of parasiticides to protect pets from parasites and minimise the risks associated with these products to the broader environment. By improving parasiticide use, we can effectively manage parasite infections while promoting the health of pets and people, and the safety of the environment.