Efficacy Of Advantage Against..

Efficacy of Advantage® Against Natural Infestations of Dogs with Lice: A Field Study from Norway Abstract A field study was performed to evaluate the efficacy of imidacloprid in a 10% spot-on formulation (Advantage®) against natural louse infestations on dogs. Lice are reported to be the most common ectoparasites in regions of the northern hemisphere. This study was conducted to evaluate the efficacy of imidacloprid (Advantage 10% spot-on) against sucking (Linognathus setosus) and biting (Trichodectes canis) lice. Advantage was topically applied following label instructions onto the skin of the dorsal midline between the shoulder blades of dogs. Louse counts were performed prior to treatment as well as 24 hours, 2 weeks, 4 weeks, and 6 weeks after treatment. Before treatment a thorough case history was recorded. The exclusion criteria required that none of the dogs be concomitantly treated with other insecticides and that insecticides not be used within the animals’ surroundings. In cases where several dogs occupied a household, all dogs were treated. On every examination, the dermatologic status and the extent of the infestation of the dogs with lice was recorded. Imidacloprid (Advantage) was highly effective against both sucking and biting lice over the 6-week trial. The duration of efficacy exceeded the egg-to-imago development period of both species of lice. Signs of remission of dermatitis and alopecia became visible to the pet owners at 2 weeks after treatment. The constant pruritus caused by the lice was seen for up to 2 to 4 weeks after treatment—even in the absence of lice.

Norbert Mencke, PhD Bayer AG Animal Health Leverkusen, Germany

For treatment of louse-infested dogs, insecticides from many different chemical classes are available, but most of these compounds have to be used repeatedly to control lice emerging from eggs that are not affected by the insecticides. The aim of the field study reported here was to show the efficacy and duration of imidacloprid (Advantage 10% spot-on) against naturally acquired louse infestations in dogs.

Materials and Methods The study was designed as a clinical field trial to evaluate the efficacy of imidacloprid (Advantage 10% spot-on) against natural louse infestations in dogs. Dogs naturally infested and presented to the veterinary clinic were applied in the study.

Dogs Dogs of different breeds, ages, and sexes were enrolled in the study. Dogs were presented to the veterinary clinic because of dermatologic problems. Dogs positive for lice were included in the study. Upon the owners’ consent, a case history was recorded and the dogs’ general health status was examined thoroughly. Before enrollment in the study, dog owners declared that no insecticides had been used on the dogs or their surroundings within the last 4 weeks. A total of 27 dogs (10 female; 17 male) were included in the study.

Introduction

Louse Infestations

Reports on ectoparasites on dogs and cats are dominated by discussion of fleas and ticks. Besides these ectoparasites of significant importance, lice on dogs are also reported worldwide. Lice are considered to be the most numerous ectoparasite on dogs, outnumbering fleas and ticks, especially in the northern hemisphere. Furthermore, in the southern hemisphere, lice are at least concomitant parasites on dogs kept under robust, outdoor housing conditions. In dogs with poor nutrition that are generally diseased or live in poor hygienic conditions, infestations with low numbers of lice hardly recognizable to the owner can progress to a major disease. In dogs, two species of lice are known: the sucking louse (Linognathus setotus, Olfers, 1816), belonging to the Anoplura order, and the chewing or biting louse (Trichodectes canis, de Geer, 1778), belonging to the Mallophaga order.

Dogs with lice were examined and the severity of the louse infestation was recorded. Infestation severity was recorded as light (+; one louse to three lice), moderate (++; four to ten lice), or heavy (+++; more than ten lice), similar to the method for measuring severity of flea infestations. Samples were taken for lice taxonomy.

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Treatment All dogs were treated according to their body weight. Imidacloprid was applied topically to the skin as described in the Advantage package leaflet for once-a-month topical flea control (Table 1). Advantage 400 (40 ml of the 10% imidacloprid solution) for dogs 25 kg and heavier by weight was not registered at the onset of the study. Investigations are currently running that show the efficacy and duration in regard to lice.

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In cases where several animals lived together in one household, all animals were treated. For animal welfare reasons, this study was designed without an untreated control group, as is usual in such field studies.

Results

TABLE 1 NUMBER OF DOGS TREATED WITH ADVANTAGE® ACCORDING TO BODY WEIGHT RANGE

Twenty-two dogs in the study were purebred hunting Dosage No. of Dogs Body Weights Volume (mg/kg body weight) Treated (kg) dogs; the remaining five were mixed breeds. The purebred hunting dogs were from the following breeds: Irish setter Advantage® 100 10 to 25 1 9.0 (dogs 4–10 kg) (eight dogs), retriever (five dogs), English setter (four dogs), Gordon setter (two dogs), small Münsterländer (two Advantage® 250 10 to 25 14 12.0–24.0 (dogs 10–25 kg) dogs), and English pointer (one dog). The majority of dogs were in the body weight range of Advantage® 250* up to 20 12 26.0–53.0 (two tubes; dogs ≥25 kg) 15 to 30 kg. Dogs with a long haircoat were predominate in this study, as indicated by the breeds (22 of the 27 dogs; *The Advantage 400 (4 ml of the 10% imidacloprid solution) for dogs ≥25 kg by weight was not registered at the onset of the study. Investigations are currently running that 81.5%). Hair length was recorded as medium for four dogs show the efficacy and duration in regard to lice, respectively. and short for only one dog, an English pointer. The recorded age of the purebred dogs included every age group from juvenile dogs (younger than 1 year) to old dogs (older than 10 years). Table 2 shows the age distribution. remission of pruritus began between days 3 and 14 after treatment. The veterinary examination before treatment recorded clinicalConcomitant therapy with corticosteroids and antibiotics was indily healthy dogs with the exception of the hair and skin lesions. All cated in five dogs at the second examination (2 weeks after treat27 dogs in the study were examined for generalized parasitic derment), and four dogs at the third examination (4 weeks after treatmatitis. Dog owners indicated on the questionnaire that 23 of the 27 ment). All four dogs examined at 4 weeks after treatment had long dogs had pruritus. haircoats; one had been scored for a heavy infestation before treatThe parasitologic examination implemented in the study includment and a severe generalized dermatitis. ed a scoring system similar to the one used for flea infestations. The results showed that 13 of the 27 dogs were scored for carrying a light louse infestation. Furthermore, eight dogs carried a moderate louse Louse infestation in dogs is the most common ectoparasitic disinfestation, and six dogs carried a heavy louse infestation (Table 3). ease in regions of the northern hemisphere. In these regions, fleas The parasitologic examination of the random samples from 15 of are often rare or even nonexistent. Infestations with lice range from the 27 dogs showed a distribution between biting and sucking lice. light to heavy and can lead to severe generalized dermatitis, dependTen of the 15 dogs were infested with T. canis; the remaining five ing on the various factors of lice transmission: hygiene, housing,

Discussion

dogs carried the sucking louse, L. setosus. The examination revealed single infestations where either the louse T. canis of the Mallophaga order or the louse L. setosus of the Anoplura order was present. There was no record of any dog carrying both louse species. These two louse species can be distinguished by the shape of their heads and mouth parts (Table 4). The veterinary examination 24 hours after treatment showed a fast onset of efficacy. This was visible to the dog owners, especially in the heavily infested dogs, where the owners reported that the dogs’ bedding was covered with what one owner called “salt and pepper.” Although the dogs were kept indoors at night because this study was conducted during winter, the owners could easily see lice falling off the dogs as a result of the treatment. At the following examinations of the dogs, 2, 4, and 6 weeks after treatment, no lice were recorded from any of the 27 dogs, which shows 100% efficacy. The clinical status of hair and skin was examined and showed a remission of the generalized dermatitis and alopecia at the second examination 2 weeks after treatment. The dog owners reported that

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malnutrition, and general health of the dog. In contrast to other authors’ reports of simultaneous infestations of biting and sucking lice on the same host, the study reported here examined only single infestations with either T. canis or L. setosus. Furthermore, results of other flea trials conducted within Europe show that when dog kennels were infested with both fleas and lice, the individual dog was infested with either fleas or lice; no dog was found to carry both ectoparasites at the same time (internal reports, data on file). Imidacloprid in a topical spot-on formulation (Advantage 10%) was effective in eliminating an existing louse infestation on dogs. Furthermore, imidacloprid was effective during the whole 6-week study and therefore exceeded the egg-to-imago development period of both louse species. This is in contrast to the insecticides currently in use, such as carbamates, organophosphates, or pyrethrins, which do not penetrate the egg shell, rendering a single treatment insufficient. Furthermore, the compounds do not maintain an effective level on dog skin or haircoat and so the following generation of

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TABLE 2

TABLE 3

AGE DISTRIBUTION OF DOGS

DISTRIBUTION OF SEVERITY OF LOUSE INFESTATION

Age

No. of Dogs

Younger than 1 year 1–3 years 4–10 years Older than 10 years Age unknown

Type of Infestation

5 9 4 4 5

No. of Dogs

Light Moderate Heavy

13 8 6

TABLE 4 CHARACTERISTICS OF THE TWO LOUSE SPECIES FOUND ON DOGS Order

Mallophaga

Anoplura

Species

Trichodectes canis and 10 more species described

Linognathus setosus, only species

Morphology

Head: rectangular shape, wider than long, flat at front Mouth part: sharp Abdomen: broad oval Color: yellowish Size: 1.5 mm Single egg on the hair

Head: slightly more narrow than thorax; overall shape: square Mouth part: round Abdomen: broad egg shaped Color: brown and white Size: 1.5 mm (male), 1.7 mm (female) Single egg on the hair, egg with a “lid”

Feeding habit

Skin squamae, secretion (blood)

Blood

Clinic

Pruritus because of very mobile louse dermatitis, eczema

Pruritus, dermatitis, eczema; anemia mainly in puppies

Location

Whole body

Head (around mouth), neck, dorsal body (often in clusters)

lice that hatches from the eggs develops undisturbed. The visible remission of louse-induced dermatologic problems in dogs commenced at 2 weeks after a single treatment with imidacloprid. Louse infestations in dogs led to an often severe pruritus that caused constant scratching and self-traumatization. This is often the starting point for a severe generalized dermatitis with secondary infections; the clinical impact is equivalent to flea allergy dermatitis for both dogs and cats. Even after treatment, a constant pruritus was reported by some dog owners, but no lice were detected during clinical examinations.

Conclusion The results of this study clearly demonstrated that diagnosing by pruritus alone is misleading, assuming an ongoing louse infestation after treatment. This study showed that pruritus persists for some time after treatment in the absence of an active louse infestation.

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Although especially light infestations with lice are often overlooked by dog owners, a regular louse control is recommended during the peak season from early autumn into spring. Regular treatment against lice reduces the increase of lice on dogs and the possibility of louse-induced dermatologic problems.

Bibliography Bowman DD: Georgis’ Parasitology for Veterinarians, ed 6. Philadelphia, Saunders, 1990, p 32. Christensson D, Zakrisson G, Holm B, Gunnarsson L: Lus hos hund i Sverige (in Swedish). Svensk Veterinartidn 50:189–191, 1998. Elbert A, Becker B, Hartwig J, Erdelen C: Imidacloprid—a new systemic insecticide. Pflanzenschutz Nachrichten (Bayer) 44:113–136, 1991. Hopkins TJ, Kerwick C, Gyr P, Woodley I: Efficacy of imidacloprid to remove and prevent Ctenocephalides felis infestations on dogs and cats. Aust Vet Pract 26:150–153, 1996. Persson L: Ektoparasiter hos hund och katt (in Swedish). Svensk Veterinartidn 25:254–260, 1973.

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