Efficacy of ADVANTAGE Against

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Suppl Compend Contin Educ Pract VetVol. 22, No. 4(A), 2000 International Flea Control Symposium

AbstractA field study was performed to evaluate the efficacy of imidaclo-

prid in a 10% spot-on formulation (Advantage ®) against naturallouse infestations on dogs. Lice are reported to be the most commonectoparasites in regions of the northern hemisphere. This study wasconducted to evaluate the efficacy of imidacloprid (Advantage 10%spot-on) against sucking ( Linognathus setosus) and biting ( Tri-chodectes canis) lice. Advantage was topically applied following labelinstructions onto the skin of the dorsal midline between the shoul-der blades of dogs. Louse counts were performed prior to treatmentas well as 24 hours, 2 weeks, 4 weeks, and 6 weeks after treatment.Before treatment a thorough case history was recorded. The exclu-sion criteria required that none of the dogs be concomitantly treat-ed with other insecticides and that insecticides not be used withinthe animals ’ surroundings. In cases where several dogs occupied ahousehold, all dogs were treated. On every examination, the derma-tologic status and the extent of the infestation of the dogs with licewas recorded. Imidacloprid (Advantage) was highly effectiveagainst both sucking and biting lice over the 6-week trial. The dura-tion of efficacy exceeded the egg-to-imago development period of both species of lice. Signs of remission of dermatitis and alopeciabecame visible to the pet owners at 2 weeks after treatment. Theconstant pruritus caused by the lice was seen for up to 2 to 4 weeksafter treatment —even in the absence of lice.

IntroductionReports on ectoparasites on dogs and cats are dominated by dis-

cussion of fleas and ticks. Besides these ectoparasites of significantimportance, lice on dogs are also reported worldwide. Lice are con-

sidered to be the most numerous ectoparasite on dogs, outnumber-ing fleas and ticks, especially in the northern hemisphere. Further-more, in the southern hemisphere, lice are at least concomitantparasites on dogs kept under robust, outdoor housing conditions. Indogs with poor nutrition that are generally diseased or live in poorhygienic conditions, infestations with low numbers of lice hardlyrecognizable 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 orbiting louse ( Trichodectes canis, de Geer, 1778), belonging to theMallophaga order.

For treatment of louse-infested dogs, insecticides from many dif-ferent chemical classes are available, but most of these compoundshave to be used repeatedly to control lice emerging from eggs thatare not affected by the insecticides. The aim of the field studyreported here was to show the efficacy and duration of imidacloprid(Advantage 10% spot-on) against naturally acquired louse infesta-tions in dogs.

Materials and MethodsThe study was designed as a clinical field trial to evaluate the

efficacy of imidacloprid (Advantage 10% spot-on) against naturallouse infestations in dogs. Dogs naturally infested and presented tothe veterinary clinic were applied in the study.

DogsDogs of different breeds, ages, and sexes were enrolled in the

study. Dogs were presented to the veterinary clinic because of der-matologic problems. Dogs positive for lice were included in the

study. Upon the owners ’ consent, a case history was recorded andthe dogs ’ general health status was examined thoroughly. Beforeenrollment in the study, dog owners declared that no insecticideshad been used on the dogs or their surroundings within the last 4weeks. A total of 27 dogs (10 female; 17 male) were included in thestudy.

Louse InfestationsDogs with lice were examined and the severity of the louse infes-

tation 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 measuringseverity of flea infestations. Samples were taken for lice taxonomy.

Treatment All dogs were treated according to their body weight. Imidaclo-

prid was applied topically to the skin as described in the Advantagepackage leaflet for once-a-month topical flea control (Table 1).

Advantage 400 (40 ml of the 10% imidacloprid solution) fordogs 25 kg and heavier by weight was not registered at the onset of the study. Investigations are currently running that show the effica-cy and duration in regard to lice.

Efficacy of Advantage ® AgainstNatural Infestations of Dogs with

Lice: A Field Study from Norway

Norbert Mencke, PhDBayer AG

Animal Health

Leverkusen, Germany



TNAVC, January 2000 Suppl Compend Contin Educ Pract VetVol. 22, No. 4(A), 2000

In cases where several animals lived together in onehousehold, all animals were treated. For animal welfarereasons, this study was designed without an untreated con-trol group, as is usual in such field studies.

ResultsTwenty-two dogs in the study were purebred hunting

dogs; the remaining five were mixed breeds. The purebred

hunting dogs were from the following breeds: Irish setter(eight dogs), retriever (five dogs), English setter (fourdogs), Gordon setter (two dogs), small M ünsterl änder (twodogs), and English pointer (one dog).

The majority of dogs were in the body weight range of 15 to 30 kg. Dogs with a long haircoat were predominatein this study, as indicated by the breeds (22 of the 27 dogs;81.5%). Hair length was recorded as medium for four dogsand short for only one dog, an English pointer. The record-ed age of the purebred dogs included every age group fromjuvenile dogs (younger than 1 year) to old dogs (older than10 years). Table 2 shows the age distribution.

The veterinary examination before treatment recorded clinical-ly healthy dogs with the exception of the hair and skin lesions. All27 dogs in the study were examined for generalized parasitic der-matitis. Dog owners indicated on the questionnaire that 23 of the 27dogs had pruritus.

The parasitologic examination implemented in the study includ-ed a scoring system similar to the one used for flea infestations. Theresults showed that 13 of the 27 dogs were scored for carrying a lightlouse infestation. Furthermore, eight dogs carried a moderate louse

infestation, and six dogs carried a heavy louse infestation (Table 3).The parasitologic examination of the random samples from 15 of the 27 dogs showed a distribution between biting and sucking lice.Ten of the 15 dogs were infested with T. canis ; the remaining fivedogs carried the sucking louse, L. setosus. The examination revealedsingle infestations where either the louse T. canis of the Mallopha-ga order or the louse L. setosus of the Anoplura order was present.There was no record of any dog carrying both louse species. Thesetwo louse species can be distinguished by the shape of their headsand mouth parts (Table 4).

The veterinary examination 24 hours after treatment showed a

fast onset of efficacy. This was visible to the dog owners, especiallyin the heavily infested dogs, where the owners reported that thedogs’ bedding was covered with what one owner called “salt andpepper. ” Although the dogs were kept indoors at night because thisstudy was conducted during winter, the owners could easily see licefalling off the dogs as a result of the treatment. At the followingexaminations of the dogs, 2, 4, and 6 weeks after treatment, no licewere recorded from any of the 27 dogs, which shows 100% efficacy.

The clinical status of hair and skin was examined and showed aremission of the generalized dermatitis and alopecia at the secondexamination 2 weeks after treatment. The dog owners reported that

remission of pruritus began between days 3 and 14 after treatment.Concomitant therapy with corticosteroids and antibiotics was indi-cated in five dogs at the second examination (2 weeks after treat-ment), and four dogs at the third examination (4 weeks after treat-ment). All four dogs examined at 4 weeks after treatment had longhaircoats; one had been scored for a heavy infestation before treat-ment and a severe generalized dermatitis.

DiscussionLouse infestation in dogs is the most common ectoparasitic dis-

ease in regions of the northern hemisphere. In these regions, fleasare often rare or even nonexistent. Infestations with lice range fromlight to heavy and can lead to severe generalized dermatitis, depend-ing on the various factors of lice transmission: hygiene, housing,malnutrition, and general health of the dog.

In contrast to other authors ’ reports of simultaneous infestationsof biting and sucking lice on the same host, the study reported hereexamined only single infestations with either T. canis or L. setosus.Furthermore, results of other flea trials conducted within Europeshow 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-weekstudy and therefore exceeded the egg-to-imago development periodof both louse species. This is in contrast to the insecticides current-ly in use, such as carbamates, organophosphates, or pyrethrins,which do not penetrate the egg shell, rendering a single treatmentinsufficient. Furthermore, the compounds do not maintain an effec-tive level on dog skin or haircoat and so the following generation of

TABLE 1NUMBER OF DOGS TREATED WITH

ADVANTAGE ® ACCORDING TOBODY WEIGHT RANGE

Dosage No. of Dogs Body WeightsVolume (mg/kg body weight) Treated (kg)

Advantage ® 100 10 to 25 1 9.0(dogs 4–10 kg)

Advantage ® 250 10 to 25 14 12.0 –24.0(dogs 10–25 kg)

Advantage ® 250* up to 20 12 26.0 –53.0(two tubes; dogs ≥ 25 kg)

*The Advantage 400 (4 ml of the 10% imidacloprid solution) for dogs ≥ 25 kg by weightwas not registered at the onset of the study. Investigations are currently running thatshow the efficacy and duration in regard to lice, respectively.



Suppl Compend Contin Educ Pract VetVol. 22, No. 4(A), 2000 International Flea Control Symposium

lice that hatches from the eggs develops undisturbed. The visibleremission of louse-induced dermatologic problems in dogs com-menced at 2 weeks after a single treatment with imidacloprid.

Louse infestations in dogs led to an often severe pruritus thatcaused constant scratching and self-traumatization. This is often thestarting point for a severe generalized dermatitis with secondaryinfections; the clinical impact is equivalent to flea allergy dermati-tis for both dogs and cats. Even after treatment, a constant pruritus

was reported by some dog owners, but no lice were detected duringclinical examinations.

ConclusionThe results of this study clearly demonstrated that diagnosing by

pruritus alone is misleading, assuming an ongoing louse infestationafter treatment. This study showed that pruritus persists for sometime after treatment in the absence of an active louse infestation.

Although especially light infestations with lice are often overlookedby dog owners, a regular louse control is recommended during thepeak season from early autumn into spring. Regular treatmentagainst lice reduces the increase of lice on dogs and the possibilityof louse-induced dermatologic problems.

BibliographyBowman DD: Georgis’ Parasitology for Veterinarians, ed 6. Philadelphia, Saun-

ders, 1990, p 32.Christensson D, Zakrisson G, Holm B, Gunnarsson L: Lus hos hund i Sverige

(in Swedish). Svensk Veterinartidn50:189–191, 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 felisinfestations on dogs and cats. Aust VetPract 26:150–153, 1996.

Persson L: Ektoparasiter hos hund och katt (in Swedish). Svensk Veterinartidn25:254–260, 1973.

TABLE 2AGE DISTRIBUTION OF DOGS

Age No. of Dogs

Younger than 1 year 51–3 years 94–10 years 4Older than 10 years 4Age unknown 5

TABLE 3DISTRIBUTION OF SEVERITY

OF LOUSE INFESTATION

Type of Infestation No. of Dogs

Light 13Moderate 8Heavy 6

TABLE 4CHARACTERISTICS OF THE TWO LOUSE SPECIES FOUND ON DOGS

Order Mallophaga Anoplura

Species Trichodectes canisand 10 more species described Linognathus setosus,only species

Morphology Head: rectangular shape, wider than long, flat at front Head: slightly more narrow than thorax; overallshape: square

Mouth part: sharp Mouth part: roundAbdomen: broad oval Abdomen: broad egg shapedColor: yellowish Color: brown and whiteSize: 1.5 mm Size: 1.5 mm (male), 1.7 mm (female)Single egg on the hair Single egg on the hair, egg with a “lid”

Feeding habit Skin squamae, secretion (blood) Blood

Clinic Pruritus because of very mobile louse Pruritus, dermatitis, eczema; anemia mainlydermatitis, eczema in puppies

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

Documents

Efficacy of ADVANTAGE Against