The bench-mark of an insecticide to be used on dogs is its efficacy against C. felis felis, while the bench-mark for an acaricide is its efficacy against the predominant or most important tick species in the country or region in which it is to be used. Thus efficacy against R. sanguineus in regions with a mediterranean, tropical or subtropical climate is a must; efficacy against I. ricinus, and to an increasing degree D. reticulatus, in Europe with its somewhat cooler northern climate, is a prerequisite; and efficacy against D. variabilis and I. scapularis in the USA is essential. Efficacy against other flea or tick species must be regarded as a bonus, so too if efficacy includes ectoparasites belonging to other groups such as mites and lice. A broad-spectrum ectoparasiticide or combination of ectoparasiticides that is effective against the diverse assemblage of parasites encountered on dogs entrains a definite benefit to dog owners, as only a single treatment or application will be necessary. Should such an ectoparasiticide, or combination of ectoparasiticides also exhibit long-term efficacy against re-infestation, the benefit to owners and their pets is even more substantial. The imidacloprid/flumethrin collar would appear to meet all these criteria.
A number of other chemicals, either on their own or in combination with others, have also proved to have a sustained efficacy lasting for shorter or longer periods of time. Spot-on formulations of pyriprole as well as a combination of cyphenothrin and pyriproxyfen, have proved to be effective against fleas and ticks for 30 to 35 days after their application [29, 33]. Efficacy against re-infestation with R. sanguineus, lasting for at least 170 days has been reported for a collar impregnated with a slow-release formulation of flumethrin and propoxur . In contrast the efficacy of the imidacloprid/flumethrin collars against re-infestation with both fleas and ticks persists for at least 8 months.
Dogs that are not confined to kennels or indoors may harbour more than one group of ectoparasites, and within each group of ectoparasites infestation with two or more species is possible. Thus in northern Greece, France and Hungary several flea species were collected from dogs and a substantial number of these animals were simultaneously infested with more than one species [35–37]. In Albania 143 dogs infested with ectoparasites harboured three flea species, two tick species, two mite species and a biting louse, and mixed infestations were common . In a kennel environment in South Africa dogs were infested with Ctenocephalides spp., and with R. sanguineus, and Matthee et al.  reported that a total of 28 tick species had been collected from dogs in various surveys conducted in that country. Although not recorded separately, several of the latter animals were simultaneously infested with as many as four tick species, while over a period of a year they may have harboured as many as nine species.
A sound knowledge of the seasonal abundance of fleas and ticks is crucial to determining the correct time to initiate chemical intervention. In both the Northern and Southern Hemisphere, infestation with fleas and ticks either commences, or escalates from a low base, during spring to reach peak numbers in mid or late summer. This peak is followed by a gradual or marked decrease in numbers towards winter. Thus at 13 veterinary practices in Hungary the proportion of dogs infested with fleas, of which the majority were C. canis, increased from 9.1% in spring to 18.1% and 19% in summer and autumn and declined to 9.9% in winter . In Albania, the proportion of dogs infested with fleas, of which most were C. canis, increased from 64.3% in winter to 75.9% in spring and 100% in summer . In South Africa infestation with Ctenocephalides spp., increased on dogs from spring to reach a peak in mid and late summer and declined thereafter to winter .
In Albania no R. sanguineus was detected on dogs in winter, whereas 34.2% of dogs were infested in spring and 50% in summer . The largest numbers of D. reticulatus and I. ricinus were collected from dogs presented at 25 veterinary clinics in Hungary during March and April and in September, and the least in January and December . The percentage of dogs, presented at veterinary practices in England, Scotland and Wales that were infested with I. ricinus and Ixodes hexagonus increased from March to reach a peak in June and declined thereafter, with a minor increase in October . In Southeastern Georgia, USA, most adult I. scapularis were collected from dogs during the colder months from October to March, and most D. variabilis in the warmer months from April to August, and most Amblyomma maculatum in July and August . In northern South Africa peak numbers of all developmental stages of R. sanguineus were recorded on dogs in a kennel environment from spring to late summer (October to April) , and a similar pattern of abundance for this tick was reported on dogs in the central region of this country .
The studies above confirm that flea infestation in both the Northern and Southern Hemisphere is generally most prevalent in the warmer months from spring to late summer. With the exception of I. scapularis in the USA, which apparently is a winter tick, the seasonality of tick infestations in both hemispheres generally mirrors that of fleas. It is thus logical that whatever mode of treatment is chosen it should commence in late winter or early spring and continue throughout the summer and into autumn. Usually this entails several treatments with parasiticides at monthly intervals throughout the activity period of the parasites. Furthermore, unless the chemical chosen is active against both fleas and ticks, multiple treatments with more than one chemical may be necessary to control both groups of parasites. The imidacloprid/flumethrin collar provides a sound alternative to a multi-treatment regimen for the control of fleas and ticks on dogs. If the collars are applied in late winter or early spring they will eliminate the existing small populations of fleas and ticks, and thereafter their sustained repellent efficacy will reduce the likelihood of re-infestation throughout the summer and into the autumn months.
The collars affect the flea and tick populations in different ways. C. felis felis can complete several generations during the year , and it is the extant population of fleas in spring that gives rise to their summer abundance. This cycle can be disrupted by applying the collars in spring and thus prevent re-infestation by successive populations. In addition the imidacloprid component of the collar that is shed on skin scales and hair of the treated dog will kill flea larvae in its bedding and resting places. Consequently the life cycle of C. felis felis will be interrupted during two critical phases. Firstly the egg-laying females are killed on the dog, and secondly the larvae, which will eventually give rise to fresh infestations with adult fleas, are eliminated in its immediate surroundings.
With the exception of R. sanguineus, which can complete two or more life cycles in a year on domestic dogs [39, 40], most three-host ticks complete only a single life cycle annually. In the case of R. sanguineus, the immediate therapeutic efficacy of a newly applied collar will only affect some of the already attached ticks. However, the sustained acaricidal efficacy of the collar will prevent simultaneous re-infestation of the dog by larvae, nymphs and adults . This will curtail the several annual life cycles completed by this tick in climates where the winters are mild and summers hot . Because domestic dogs are for all practical purposes the only hosts of R. sanguineus, re-infestation of premises inhabited by a collared dog can only take place via an untreated dog. Even then any resulting re-infestation of the resident collared dog will be prevented by the long-term activity of the collar.
In the context of the other three-host ticks that infest dogs, their life cycles usually take a year to complete, and the immature stages of some of these tick species prefer rodents as hosts. Thus killing the adults on dogs during the summer will not only provide immediate relief to the dogs, but will also reduce the numbers of larvae and nymphs that are available to infest rodent hosts. This reduction of infestation on rodent hosts should translate into a lower level of infestation with adult ticks on dogs in the following year.
The adults of some three-host tick species have a wide range of hosts including dogs. In Europe these ticks include D. reticulatus, I. ricinus, I. hexagonus, in the USA A. americanum, D. variabilis and I. scapularis, and in southern Africa Haemaphysalis elliptica and Rhipicephalus simus. Thus although dogs may be protected from infestation within their immediate environment by the application of imidacloprid/flumethrin collars, they will be challenged by adult ticks of these species whenever they exercise with their owners, or are involved in hunting, or in any other outdoor activities. However, as demonstrated in the clinical trials above, they will be protected against this challenge by the sustained repellent efficacy of the collars, even if it is raining or if they go for a swim.
The immediate effect of the imidacloprid/flumethrin collar on an existing population of C. felis felis on dogs, and its sustained preventive efficacy, coupled with the larvicidal efficacy of imidacloprid residues in the dog’s immediate surroundings, result in interesting secondary benefits. One of these benefits is that the chances of a collared dog developing flea allergy dermatitis from repeated flea bites is significantly reduced. This stems from the fact that fleas that might re-infest the dog are killed within two hours, probably before they can start feeding. Moreover, Rust et al. have demonstrated that cat hair treated with extremely small amounts of imidacloprid actually inhibits feeding by adult C. felis felis.
Other secondary benefits are at present speculative, but are likely to be thoroughly researched in the future. One of these is that the off-host lethal effect of imidacloprid against flea larvae precludes the possibility of the larvae ingesting the eggs of the cestode D. caninum. This will break the life cycle of the cestode prior to infection of the intermediate flea host. Even if fleas infected with the cysticercoids of D. caninum should get onto a collared dog, they in turn may be killed so rapidly that the dog would be unlikely to swallow one while nibbling at its skin.
The prevention of the transmission of tick-borne diseases by infected ticks, caused by the speedy repellent efficacy of the collars, is also still speculative. However, because efficacy is already evident within 6 h of re-infestation it would seem unlikely that infected ticks would have had time to transmit whatever organisms with which they may be infected to the collared dog. Should a dog already be infected with a tick-borne disease, application of an imidacloprid/flumethrin collar will not affect the course of the disease as the tick vector will most probably already have detached. However, application of the collar at this time may protect the dog against re-infection by eradicating other ticks infected with the same organism should they climb on to it. If there are other dogs in the same household as the sick dog, they must be fitted with collars. This will assist in protecting them against infestation with ticks that may be infected with the same pathogen.
Shaw et al.  have listed the various tick-borne diseases that affect dogs in different regions of the world and also the ticks responsible for transmitting the causative organisms of these diseases. Not surprisingly, R. sanguineus is involved in the transmission of several of them, namely Babesia canis Babesia vogeli Babesia gibsoni Hepatozoon canis Ehrlichia canis and Rickettsia conorii. D reticulatus is responsible for the transmission of B. canis in Europe and D. variabilis for the transmission of Ehrlichia chaffeensis and Rickettsia rickettsii in the USA . Recent studies indicate that the distribution range of D. reticulatus in several European countries as well as in Britain is expanding [9, 15, 28]. This has led to cases of canine babesiosis being detected in regions where the disease had previously not been encountered . In the light of these findings treatment of dogs for ticks is even more imperative. Treatment that kills ticks and thus reduces the effective population that can transmit disease is essential. If, however, it can be proved that the rapid killing of infected ticks on dogs within six hours of infestation could actually prevent transmission of disease, this would be a huge step forward.