6 Jun 2023
Ian Wright
Job Title
Some animals require a parasite control risk assessment based on geographic and lifestyle factors. Image © Caitlin Barnett
Parasites in cats and dogs can be a source of revulsion, distress and irritation to pet owners. They can also cause or transmit disease to both humans and pets.
Control of pet parasites is, therefore, vital, and requires consideration of pet and owner lifestyle to assess risk and the most effective products for the individual. Because endectocide products treat multiple parasites, they have sometimes received a bad press for encouraging “blanket treatment”. Where control of multiple parasites is required, however, they are useful tools that may improve compliance and reduce costs for owners.
UK cats and dogs are exposed to a wide range of parasites, such as fleas, Toxocara species, Echinococcus granulosus, Angiostrongylus vasorum and tick-borne pathogens, which may cause significant disease in pets or present zoonotic risks to owners.
Parasite prevention is, therefore, essential to reduce these disease risks and to avoid erosion of the human-animal bond. Revulsion at visible parasites, irritation through flea bites and awareness of zoonotic risk without effective preventive measures can reduce this bond, and all the psychological and physical benefits it brings.
Effective parasite control will also bond clients to the practice where future advice and parasite prevention will then be more likely to be sought.
Routine parasite control, therefore, forms a vital part of pet health programmes, with some parasites requiring year-round preventive treatment in all pets and others requiring a risk assessment based on geographic and lifestyle factors.
Year-round treatment for all parasites in all cats and dogs, known as “blanket treatment”, has a number of drawbacks, including potential unnecessary expense for owners and drug exposure to pets. It may also potentially lead to increased environmental contamination with parasiticides, although this has yet to be quantified.
In this context, endectocides (drugs or products with endoparasiticide and ectoparasiticide activity) can be viewed as inevitably leading to over-treatment.
This is true if the parasite control needs of a pet are limited to one or two parasites, but where multiple parasite control is required, endectocides provide an opportunity to limit the number of products clients need to administer. This can increase compliance and reduce cost.
Strategies to limit parasitic disease rely on a combination of practical control measures and preventive drug treatments, and these form the basis of parasite control protocols for individual pets.
Parasite control programmes allow bespoke advice to be formulated based on regional risk and lifestyle of the pet. Asking questions surrounding lifestyle and owner preferences will also help to maximise compliance – and, therefore, the effectiveness of any recommended treatment.
Some parasites with animal health and zoonotic implications are ubiquitous, and exposure is practically impossible to avoid. For UK cats and dogs, this is true of Toxocara (with the potential exception of indoor cats) and cat fleas.
For this reason, and the zoonotic risk they represent, regular treatment for Toxocara and fleas is essential, and should form the basis of all cat and dog parasite control programmes. Other parasite prevention is risk assessed on the basis of lifestyle and geographical distribution.
Parasites to consider in the UK would include ticks (Ixodes species, Dermacentor reticulatus), tapeworm (Dipylidium caninum, Taenia species, E granulosus) and lungworm (A vasorum).
The need for monthly treatment for Toxocara (as opposed to quarterly) and preventive treatment for ticks, lungworm and tapeworm should be based on the following considerations.
It can be concluded from these risk factors that, for many pets, blanket treatment is inappropriate.
Some pets will only require flea treatment, whereas others may require protection against multiple parasites, but not all parasite groups. Indoor cats are an example where only flea treatment may be required. Visiting pets, stray cats, wildlife and people that have activated pupae may all bring fleas into homes containing indoor cats. Central heating allows environmental stages of the flea life cycle to persist all year round in the home.
This combination of factors leads to increased flea challenge on domestic pets and, without routine preventive treatment, a high risk exists of flea infestations establishing. If fleas are left untreated, even low numbers will also lead to rapid establishment of household infestations with potential for transmission of zoonotic pathogens, such as Bartonella species and Rickettsia felis (Abdullah et al, 2019; Dryden et al, 2000).
Indoor cats, however, are unlikely to be exposed to other parasites, and Toxocara risk can be managed through good hygiene around litter trays and responsible disposal of faeces.
A monovalent product would be most suitable in these circumstances, although frequency of bathing/shampooing should be checked if a fipronil or imidacloprid product is going to be used. Many dogs will require monthly roundworm treatment because they live with young children or are at risk from lungworm. Far fewer will fulfil the specific criteria for tapeworm treatment, however, and tick risk will vary from dog to dog.
This is where endectocides that treat fleas and roundworm, but not tapeworm, such as selamectin, isoxazoline/macrocyclic lactone combinations or imidacloprid/moxidectin spot-on treatments are extremely useful.
Some cats and dogs require parasite prevention against all four major parasite groups, but for dogs, a product that is effective against all of them has yet to be developed.
This is not true for cats, though, where two spot-on formulations are available. These can be considered for hunting cats where all four of these parasite groups are likely to be an issue, while also considering other factors, such as compliance.
These products should not be used in pregnant and lactating cats where safety studies in pregnancy/lactation have not been carried out, or where use in pregnant cats is contraindicated.
Clients seeking advice from veterinary practices regarding flea and tick control will want it to succeed, yet poor compliance is a common reason for flea and tick control failures (Gates and Nolan, 2010).
Understanding the reasons for this will then allow measures to be put in place to try to improve owner compliance. Reasons for poor compliance include difficulty administering products, forgetting to administer them, and cost and concern over side effects. Endectocides can be useful in managing each of these drivers of poor compliance where control for multiple parasites is required. It is vital clients feel confident administering a product and in its efficacy, and product choice is key to improving the ease with which clients can administer a product.
A number of points can be discussed with the client when choosing a product and whether an endectocide would be beneficial.
Owners may have concerns regarding adverse events from personal experience of using products, or from reported adverse events in the press or on social media. Some of these events may represent true adverse reactions, whereas others may have no link to the product.
Any real or perceived event will make owners reluctant to use products, and any concerns should be taken seriously. Any suspected adverse event in the practice should be reported, and the owner reassured it will be taken seriously and investigated. If concerns arise from reported cases that have occurred elsewhere then it is important to emphasise to clients that while adverse events can occur when any product is used, they are rare for licensed products used as indicated.
In the case of endectocide products containing more than one compound, owners should be reassured that safety studies will have been carried out to ensure combination of products are as safe as possible, as long as data sheet guidance is followed.
Few veterinary professionals would argue that all cats and dogs need to be treated against all parasites all of the time.
Teacup dogs transported in handbags and fed cooked diets are unlikely to ever need tapeworm treatment. Dogs living in areas where lungworm is absent will not require protection from it. Similarly, cats living indoors with adequate flea prevention will be safe from the perils of tapeworm and tick exposure.
For these pets, broad-spectrum endectocide use would represent over-treatment, and so it remains vital that effective, but more targeted treatments are also available.
Therefore, endectocides do not represent panacea cure-all treatments, which all cats and dogs need, but neither do they mean over-treatment for every cat and dog that receives them.
They are a tool to be used strategically after a lifestyle and geographic risk assessment has been made.
Evidence gaps exist, which means such assessments are not always easy or even possible, but the existence of both monovalent products and endectocides gives veterinary professions the flexibility to implement the level of protection they believe each pet needs based on the latest evidence.
