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3 : Ectoparasitic skin diseases

Mechanical measures

Mechanical measures like cleaning and vacuuming (remembering, firstly, to remove cushions from armchairs and settees) are essential preliminary measures that have long been underestimated. Outside, damp, shady areas, frequented enough by cats and dogs to be contaminated by eggs and flea faeces (main food supply for the larvae), should be eliminated.

Chemical measures

Insect Growth Regulators (e.g. methoprene, pyriproxyfen and fIufenoxuron) act on non-parasitic stages. They come in various formulations. Foggers enable a large volume of product to be dispersed in the envifonment. Initial cleaning is still necessary, in order to reach larval forms which are positively geotropic and negatively phototropic. In most cases, sprays must be used in association with foggers in order to treat the morę inaccessible regions.

Adulticides, whether or not they are micro-encapsulated, stay on surfaces when sprayed in the environment. They do not penetrate carpets to reach the non-parasitic stages (especially cocoons). On the other hand, these adulticides do kill adults that emerge regularly from their cocoons, before they are able to find a host. Most available environmental preparations, therefore, combine an adulticide with an IGR.

Sodium polyhorates (activated orthoboric acid) come in powder form and are used in Great Britain and the United States for environmental treatment. They work by abrading the flea cuticle and then by desiccation. They have considerable larvicidal activity and a very prolonged residual action (over a year) provided they are applied by specialist applicators^l6.

Control strategy

Prescribing the right flea control products reąuires good clinical knowledge and a thorough understanding of the parasite. The level of parasitic infestation determines the extent of the control programme which can rangę from simple application of insecticide on the cat to intensive, combined therapy involving animals and environment, employing mechanical and Chemical measures. Strategy must also be adapted to the animaTs life style (e.g. where it goes, points of entry, presence of in-contacts). If the surroundings are completely enclosed (e.g. a fiat), the use of IGRs is justified and effective. If the cat has FAD, flea control should be aimed at completely eliminating the parasite and preventing its re-appearance, by treating the cat, in-contact animals and the environment.

Flea infestation

In heavy infestations, it is best to eliminate most fleas rapidly with a topical insecticide, whatever its modę of action, or nitenpyram. To avoid permanent reinfestation, a residual insecticide should then be used in association with an IGR for at least 6 months. Other animals (dogs and cats) in the house should also be treated.

For the occasional or less severe infestation, any insecticide will be effective, provided it is used correctly. If the infestation persists, or if there are other animals in the house, IGRs should be prescribed. In some cases, treatment of non-parasitic stages in the environment is necessary.

Flea allergy dermatitis (FAD)

The first phase consists of treating the FAD. Even without symptomatic treatment, insecticidal treatment should provide rapid relief for cats being bitten by fleas, and remission from clinical signs should be seen within 3 weeks. Here, the ideał insecticide should have a repellent and/or antifeeding effect, a knock down effect and a flushing effect. Using systemically-acting products (e.g. lufenuron) at this stage is pointless. Products with a good knock down effect and rapid antifeeding action (e.g. permethrin) are theoretically better than long-lasting residual products but are contraindicated in the cat due to their potential toxicity. Moreover, it has been demonstrated in the dog that long-acting products with less marked knock down and antifeeding actions than permethrin are actually morę effective. This efficacy is associated with a substantial, albeit morę gradual, reduction in the level of infestation which falls below the allergenic threshold for signs to develop. This threshold varies from one animal to another and does not usually consist of just one flea. Furthermore, the absence of sudden reinfestation contributes to clinical remission. Whatever product is used, it is best to increase the freąuency of application (e.g. fipronil should be given every 3 or 4 weeks). In addition to treating the affected cat, flea control must involve treating the environment and all in-contact animals. The use of products like fipronil or imidacloprid which have residual activity, also enables control of some non-parasitic stages in the environment.

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