Is year-round flea control necessary in the UK?

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Abstract

The cat flea Ctenocephalides felis remains at high prevalence on UK cats and dogs, with a milder climate and centrally heated homes allowing year-round activity.

Fleas are a source of revulsion, distress, and irritation to pet owners, but can also cause disease in pets and owners alike. Year-round flea control is, therefore, important both for animal and human health.

Keywords: Fleas, parasite control, prevention

Introduction

Flea control is often perceived as seasonal. The cat flea (Ctenocephalides felis) depends heavily on warmth and humidity to reproduce, feed, and survive, making seasonal fluctuations more likely.

Exposure to cat fleas, however, can occur at any time of year, with disease in pets and people occurring as a result.

It is important that pet owners understand how these parasites are transmitted and why year-round protection is important. It is also important that ectoparasiticides are selected and applied effectively to limit environmental contamination while achieving effective control.

Different approaches in UK and Europe

European Scientific Counsel Companion Animal Parasites (ESCCAP) recommends a year-round treatment approach in the UK, but a risk-based approach Europe wide. So, why is this?

Temperatures below freezing are lethal to adult fleas, with them dying within 5 days at -1°C and 10 days at 3°C. Survival significantly increases when temperatures exceed 8°C, where nearly half of emerged adults stay alive for 20 days (Silverman and Rust, 1983).

Eggs and larvae are also highly susceptible to cold temperatures, with larvae dying 10 days post-hatching at 10°C (Silverman et al, 1981). The effects of cold temperatures in winter in many countries therefore create a seasonal pattern for flea infestations.

Humidity is also an important factor, with many European countries being significantly drier seasonally than the UK. These effects are partially limited by the protection that fur on hosts offers and by centrally heated homes. The optimal humidity and temperatures that most UK homes are kept at mean that flea populations are sustainable all year round.

As climate changes, the trend towards milder winter temperatures seen in the UK increases the opportunity for outdoor flea life stages to survive and continue to develop.

These factors mean that, in the UK, flea populations are unlikely to show marked seasonal variations. Even where seasonal fluctuations in exposure do occur, they would have to be significant enough to prevent infestations establishing over time for year-round flea treatment not to be required.

Although real-time data from veterinary practices has found decreasing risk with season and age, flea infestations were found to occur at any age and year round (Farrell et al, 2023).

Even households with purely indoor cats may be infested by owners triggering outdoor pupal emergence through their heat and movement, and then bringing newly emerged adults inside on clothing. In a similar fashion, cats visiting multiple households may be infested by newly emerged adults outdoors and then bring them indoors into a number of different homes.

Year-round prevention is, therefore, required, as without it a high risk of flea infestations establishing exists (Coles & Dryden 2014), with cat fleas also present across the UK (Abdullah et al, 2019).

Why is prevention of flea infestations required?

Prevention of flea infestations is required to prevent a range of impacts on both animal and human health. These include:

Bite irritation – on both pets and humans (Figure 1)
Flea allergic dermatitis – still a common form of allergic dermatitis in UK cats and dogs.
Flea-borne pathogen transmission – fleas are a cause of allergic dermatitis and vectors for a variety of infections, including Bartonella henselae (cause of cat scratch disease), Rickettsia felis (cause of spotted fever), Haemoplasma species (cause of feline infectious anaemia) and Dipylidium caninum tapeworms. A total of 11.3% of flea infestations on UK cats and dogs have been found to be positive for Bartonella species (Abdullah et al, 2019). People are thought to be exposed to this pathogen primarily through flea faeces, making flea control vitally important for preventing zoonotic exposure.
Erosion of the human animal bond – through physical revulsion and fear of both disease and flea bites.

Figure 1. Flea bite reaction

Figure 2. flea dirt from an infested cat's coat.

It has been suggested that year-round flea treatment could be replaced by flea combing and treating on the basis of the presence of fleas (Figure 2). If this strategy is employed, then exposure to fleas will have already occurred, with the potential for bites and pathogen transmission.

Each female flea can lay up to 50 eggs per day, so even small delays in detection will lead to considerable flea infestation that may take months to clear.

To effectively prevent flea reproduction, a flea adulticide product must:

Kill fleas quickly enough to prevent egg laying.
Having 100% efficacy is not sufficient if the fleas are able to reproduce before they are killed. Adult fleas can lay eggs within 24 hours, so effective adulticides must kill fleas at least within that time.
Be applied often enough to continue to prevent egg laying.
The time after application at which fleas survive long enough in the presence of the product to lay eggs is known as the “reproductive break point”. If the reproductive break point is reached, then flea control will fail.

Multiple factors need to be considered when considering which flea product to select for an individual pet, both to maximise efficacy and owner compliance, while also limiting environmental contamination. These are:

Does the owner shampoo the pet or does the pet regularly swim?
The efficacy of spot-on compounds and collars not systemically absorbed may be affected by shampoos or frequent bathing/swimming. Loss of product from the pet in this way may also lead to environmental contamination. Even for spot-on products that are systemically absorbed it is important to follow data sheet advice regarding timing after application that shampooing or water emersion should be avoided.
Does the owner prefer a tablet, spot-on preparation or collar?
Some pets may have a history of skin reactions or vomiting after previous administration of parasite control products. The owner may also feel more able to apply some forms of medication than others. Applying a product in the surgery to maximise efficacy may be required where all forms of treatment are difficult for the owner to apply.
What other parasite prevention is required?
Endectocides or products containing more than one parasiticide may be beneficial to improve compliance if prevention against other parasites, such as roundworm, tapeworm, ticks or lungworm, is required.

Conclusion

Year-round flea control is important in terms of limiting zoonotic disease, improving animal health and strengthening the human-animal bond.

Understanding the reproductive break point, compliance and potential environmental impacts are all essential when discussing flea control and considering product selection.

References

Abdullah S, Helps C, Tasker S, Newbury H and Wall R (2019). Pathogens in fleas collected from cats and dogs: distribution and prevalence in the UK, Parasites and Vectors 12(1): 71.
Coles TB and Dryden MW (2014) Insecticide/acaricide resistance in fleas and ticks infesting dogs and cats, Parasites and Vectors 7(1): 8.
Dryden MW, Denenberg TM and Bunch S (2000). Control of fleas on naturally infested cats and dogs and in private residences with topical spot on applications of fipronil and imidacloprid, Veterinary Parasitology 93(1): 69-75.
Farrell S, McGarry J, Noble PM, Pinchbeck GJ, Cantwell S, Radford AD and Singleton DA (2023). Seasonality and other risk factors for fleas infestations in domestic dogs and cats. Medical and Veterinary Entomology 37(2): 359-370.
Silverman J and Rust MK (1983). Some Abiotic Factors Affecting the Survival of the Cat Flea, Ctenocephalides felis (Siphonaptera: Pulicidae). Environmental Entomology 12(2): 490-495.
Silverman J, Rust MK and Reierson DA (1981). Influence of temperature and humidity on survival and development of the cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae), Journal of Medical Entomology 18(1): 78-83.