Flea infestations - treating the environment

 
 

Many veterinary practices sell flea sprays or advise on their purchase for elimination of the environmental stages of a flea infestation. Several brands of flea spray are available, but some are being taken off the market (HSE 2018). 

By doing this module you will:

  • Understand the lifecycle of the cat flea.

  • Know the options available for treating a flea infestation.

  • Be aware of the evidence on the efficacy of environmental treatments.

  • Understand why some products are being taken off the market.

  • Know where to find out which products are authorised for sale.

The cat flea (Ctenocephalides felis) – the commonest cause of flea infestations in cats and dogs – thrives in the UK. Fleas bites can cause discomfort and are a common cause of allergic dermatitis in pets. Fleas are vectors for the tapeworm Dipylidium caninum and Haemoplasma spp (the cause of feline infectious anaemia). Although cat fleas cannot live and reproduce on people, they can bite leading to skin irritation. They are also a vector for organisms that can infect humans, including Bartonella spp (the cause of cat scratch disease) and Rickettsia felis (the cause of spotted fever). A flea infestation is unpleasant and can affect the human-animal bond. Flea control is therefore crucial in reducing disease risk and maintaining a strong healthy relationship between pet and owner. 

Having a good understanding of the flea life cycle is essential to successful flea control . Veterinary professionals have an important role in educating owners about the flea lifecycle and giving accurate advice on flea control.

  • Adult fleas can begin to lay eggs within 24–48 hours of their first blood meal and they normally lay around 24–28 eggs per day, mostly at night (Kern et al.1992; Dryden 1994). 

  • The eggs, which are not sticky, fall off the animal as it moves or grooms itself. They hatch 1–10 days later (depending on temperature and humidity) (Blagburn & Dryden 2009).

  • The resulting larvae are free-living and feed on adult flea faeces containing large amounts of incompletely digested blood, which is deposited in the environment from the infested host. The larvae also feed on organic debris and on flea eggs in the environment (Blagburn & Dryden 2009).

  • Flea larvae move away from direct sunlight to dark areas in their environment – e.g. deep into carpet fibres, animal bedding or soft furnishings, or into floorboard cracks or under skirting boards, where there is also a more humid microclimate. Outside they may go under grass, branches, leaves or soil. Flea larvae are very susceptible to heat and drying out and need a moist environment to survive. Larvae are most likely to survive where the host spends enough time to allow flea faeces to fall into the environment and provide a food source for the larvae.

  • In the following few days larvae undergo two moults before spinning a silken cocoon and moulting to the pupal stage. 

  • Adult fleas can emerge from pupae within 1–2 weeks. Under most household conditions, the whole flea lifecycle can be completed in 3–8 weeks (Blagburn & Dryden 2009). 

  • If conditions are unfavourable the pupae can remain viable for several months. Debris from the environment sticks to the cocoon making them more resistant to adverse environmental conditions and insecticides. This means that an infestation can be established even if mammalian hosts have been absent for some time. Pupae hatch in response to heat and movement and so are reactivated by the presence of possible hosts. This includes a wide range of mammals including cats, dogs, rabbits, ferrets and wildlife such as foxes and hedgehogs. 

  • Adult fleas that have emerged from dark areas move towards a light source. They then jump when the light source is suddenly and temporarily interrupted or if they detect vibrations that indicate a potential host. If the newly emerged adults do not immediately acquire a host, they can survive several days before requiring a blood meal. Once on the host, the flea starts to feed within seconds or minutes, and mates within 8 to 24 hours (Blagburn & Dryden 2009). 

The speed and reproductive potential of the lifecycle means that just a few adult fleas can lead very quickly to heavy environmental contamination of homes, particularly when temperatures are higher. Central heating in the home means that fleas can be active all year round and the higher temperatures speed up the lifecycle. By the time fleas have been found on the animal, an infestation may have already established in the home. 

Flea control hinges on simultaneously treating all the susceptible animals in a household with an effective flea adulticide. The products must be administered frequently enough (check the product information) to continue to prevent flea egg laying. 

It can take several months to effectively control an infestation, and so it is important to help the client understand this. (Click here to read a case report of fleas on treated cats in a new home in Preston). In a randomised controlled trial in which naturally-infested dogs in homes in Florida were treated with a monthly spot-on (containing imidacloprid or fipronil) for 3 months, flea counts on the dogs reduced by 90–98% within 1 week of treatment, but the same reduction in flea counts in the home environment did not occur until 1 month after treatment; fleas in the environment were not eliminated completely after 3 months’ use of either product (Dryden et al 2000) 

An alternative to an adulticide is to treat all susceptible pets continuously with lufenuron (Program), which prevents flea eggs from hatching after fleas have fed on the treated host. However, this does not kill adult fleas, so an adulticide is also needed to reduce adult flea load in an existing infestation.

Anything that helps to reduce the number of eggs and larvae will in turn reduce the number of pupae in the environment, which in turn will reduce the time needed to bring an infestation under control and reduce the number of flea bites that pets and owners receive and the risk of vector-borne disease transmission. 

The ideal method for eliminating the environmental stages would be as effective against flea pupae as it is against larvae and eggs, and it would persist in the environment, while being safe for pets, people and the environment. However, no single method fulfils all these criteria. The options for environmental control include the following:

  • Physical cleaning - Vacuuming has been shown to be useful in reducing and killing pupae, eggs and larvae in households (Hink 2007). However, vacuuming is unlikely to be effective on its own for dealing with an infestation (Jones et al 2014). Washing pet bedding at 60 degrees Centigrade will also help to reduce environmental stages (Blagburn & Dryden 2009). There is no evidence that conventional household cleaning products have any impact on flea life stage numbers.

  • Environmental pesticides – Products containing pyrethroid insecticides are used to treat the infested environment directly and will reduce larvae and egg numbers significantly if exposure to the insecticide is adequate. The pyrethroid drugs in the products include cypermethrin, deltamethrin, permethrin and tetramethrin. Some products contain a pyrethroid in combination with an insect growth regulator, or alone at higher concentrations in “flea bombs” or fogging devices. Pest control companies use products containing pyrethroids to fumigate homes with large infestations or sources of infestation that are difficult to access. The adulticide selamectin (in Stronghold spot-ons for cats and dogs) has an ovicidal and larvicidal effect. It is absorbed from the spot-on into the animal’s body and can kill larvae in the environment through being present in shed hair, skin debris and flea faeces (Stronghold SPC).

  • Insect growth regulators - This group includes methoprene, S-methoprene and pyriproxyfen. The drugs act by interfering with the hormonal control of growth in immature fleas, preventing development from one larval stage to the next and leading to larval death. Insect growth regulators are included in flea sprays in combination with pyrethroids. They are also used in combination with adulticides in spot-on preparations, from which they are shed into the environment after application to the pet (e.g. Broadline, Frontline Combo, Fiprotec Combo, Vectra 3D. See the Parasiticide Guide for other examples). 

  • Dimeticone – Dimeticone is a synthetic oil (silicone) used in a wide range of products (from contact lenses to shampoos) and in insecticide-free head-lice treatments. The use of dimeticone in spray form has been developed as an environmentally-friendly alternative to insecticides. It has the advantage of being able to be used if there are pet invertebrates or fish in the household. It works by creating a surface film of dimeticone on adult fleas and larvae, so inhibiting movement of the cuticular joints and causing immobilisation (Jones et al 2014). Adult fleas can be prevented from emerging if cocoons are adequately exposed. In one controlled study of a simulated household carpet treatment, an aerosol spray containing dimeticone 0.4% (Flee) was not significantly different from a spray containing permethrin 0.5% + pyriproxifen 0.05% (Indorex) in preventing the emergence of fleas; both treatments were highly effective (Jones et al. 2014). However the dimeticone spray has not been shown to last more than 3–4 weeks after application. 

When treating the environment directly, all areas where pets frequent, such as cars, furniture and bedding must be treated, paying particular attention to areas in, and around, which the animal sleeps, because these areas will have the greatest concentration of eggs and developing stages. Effective penetration of chemicals from aerosol products can be poor unless used from the correct distance and after removal of obstructing objects such as children’s car seats, pillows, and cushions. These should be treated separately. 

Care must be taken when using insecticide products because of the potential for pyrethroid toxicity. Fish, invertebrates and cats are particularly susceptible but any animal may be affected. Therefore pets should be removed from the areas to be treated and fish and invertebrates removed from the premises before treatment. Treated areas should be well ventilated during treatment and for at least 1 hour afterwards. 

No central agency regulates efficacy standards for flea sprays but companies producing flea sprays make claims about the duration of effect from their own studies. Claims commonly include activity against environmental flea life stages for 6 months and larval growth regulation for 12 months. 

There is little comparative information on flea sprays, or studies comparing different infestation treatment strategies, including pet treatment with or without environment treatment. It is assumed that pyrethroids and growth regulators will reduce flea biomass in the environment over time and that this will reduce the time needed to eliminate an infestation if an effective adulticide is also being used on susceptible animals in the home. 

Environmental flea sprays containing insecticides are classed as biocidal products, which are regulated by the Health and Safety Executive. Since 1998, when biocides were under the UK Control of Pesticides Regulations (COPR), regulation has been transferred to the EU and now comes under the EU Biocides Regulation (BPR, Regulation (EU) 528/2012) (HSE 2018).The change has required all active substances used in biocidal products to be reviewed and approved at an EU level, an ongoing process that is expected to continue until 2024. Products containing dimeticone are exempt from regulation under this Directive because they fall within the classification of a physically-acting approach (Jones et al 2014). As a result of the regulatory changes, which have required companies to submit dossiers on their products, some companies have opted to reformulate products or take their products off the market. Some products are no longer available, and the following are being discontinued:

  • Acclaim – Cannot be sold since 2 July 2018, but customers can continue to use legally until 3 January 2019. 

  • Indorex – Cannot be sold after 28 December 2018, but customers can continue to use until 30 June 2019.

The regulatory changes will have a negligible effect on environmental treatment options because similar products will continue to be available: for example, Beaphar Home Flea Spray; Frontline Homegard Spray; Permaguard, RIP Fleas Extra, Staykil (reformulated).

Veterinary professionals need to keep up to date with flea spray availability as legislation changes. Up-to-date Information about the regulatory status of environmental flea sprays can be found in the COPR database

When tackling an established flea infestation, reducing the flea lifecycle stages from the environment through physical cleaning, hot washing of bedding and use of environmental sprays is probably a helpful adjunct to using flea control products on pets. The products available for treating the environment contain insecticides, insect growth regulators or dimeticone. We know surprisingly little about the efficacy of environment treatments in tackling flea infestations, including the comparative efficacy of different products or strategies. A good understanding of the flea life cycle is crucial to managing an infestation and a clear explanation should help manage client expectations. 

Regulatory changes mean that some flea sprays are being taken off the market voluntarily by suppliers. Veterinary practices currently using these products will need to adapt accordingly. There is still a window of opportunity for practices to sell existing stock and for clients to legally use it. Once existing stocks expire, practices will be able to offer alternatives with similar ingredients. Clients should be reassured that any alternatives are likely to have similar efficacy and that previous products have been withdrawn due to legislative changes rather than any concerns about lack of efficacy or safety. 

PODCAST

If you prefer, you can listen to the whole audio presentation of this module using the following podcast. Don't forget that you can also download the podcast to your iPod, music player, tablet or smartphone using the Download link on the right of the audio player.

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How we produced this module

Our modules start with a detailed outline and electronic literature search. We commission a collaborating author, who is a specialist in the module topic, to write a draft module. The collaborating author on this module was Ian Wright. The draft is circulated unsigned to a wide range of commentators, include practising first-opinion vets, other topic specialists, the companies that market any mentioned drugs and other organisations and individuals, as appropriate. They can raise points about the interpretation of evidence, ask questions that are important to clinical practice, and present alternative viewpoints. There is a rigorous editing and checking process and the result is a module that is evidence-based, impartial and relevant to clinical practice. The final module is unsigned because it is the result of collaboration. 

References

Blagburn BL, Dryden MW. Biology, treatment, and control of flea and tick infestations. Vet Clin Small Anim 2009; 39: 1173–200.

Dryden MW, Rust MK. The cat flea: biology, ecology and control. Vet Parasitol 1994; 52: 1–19.

Dryden MW et al. Control of fleas on naturally infested dogs and cats and in private residences with topical spot applications of fipronil and imidacloprid. Vet Parasitol 2000; 93: 69-75.

Health and Safety Executive. Revision of the Biocidal Products Directive (98/8/EC) [online].

Health and Safety Executive. COPR database [online]. [Accessed 28.9.18

 Hink WF. Vacuuming is lethal to all postembryonic life stages of the cat flea, Ctenocephalides felis. Entomol Exp Appl 2007; 125: 221–2. 

Jones IM et al. 0.4% dimeticone spray, a novel physically acting household treatment for control of cat fleas. Vet Parasitol 2014; 199: 99-106. 

Kern WH et al. Diel patterns of cat flea (Siphonaptera: Pulicidae) egg and fecal deposition. J Medl Entomol 1992; 29: 203-6.

Stronghold. Summary of product characteristics.