louse infestation (pediculosis) in pet animals

Companion Animal Vol 16 March 2011 49© 2011 Blackwell Publishing Ltd

INTRODUCTIONLice are small (1-2 mm), dorsoventrally flattened,wingless insects. They are host-specific, obligateparasites and spend their entire life cycle (about threeweeks) on the host. Lice are reported to be increasingin number in Western Europe, and in northernScotland, they are more common than fleas.

LICE IN DOGSTwo species of lice are found in dogs in the UK,Trichodectes canis (family Mallophaga), the biting orchewing louse (Fig. 1), and Linognathus setosus (familyAnoplura), the sucking louse. In Australia and sometropical countries, another biting louse, Heterodoxusspiniger (family Boopidae), can be found. Transmissionis usually by direct contact between dogs althoughimmature lice can survive for up to three or four daysoff-host, long enough to be transmitted indirectly viabrushes, combs and bedding. Neglected animals inovercrowded, dirty conditions are particularlysusceptible.

Trichodectes feeds on hair, skin debris, scale andinflammatory exudate. It can act as intermediate hostfor the tape worm, Dipylidium caninum. Linognathusfeeds on blood, lymph and inflammatory exudate.Lice are typically found at the base of hairs, and adultlice have a claw at the end of each foot enablingthem to stay attached.

Eggs (nits) are laid by females at the base of hairs andattached firmly to the hairs by cement. They areabout 1 mm long, whitish and operculate (Fig. 2),and hatch out within about six days to produce

nymphs which then moult three times beforebecoming adults. Each female lays about 300 eggsand can live up to eight weeks.

Clinical features of louse infestation in dogsLice are most commonly found around the head andback, accumulating under mats of hair, and aroundthe pinnae (Fig. 3). Pruritus with poor coat andalopecia are classic features although severity ofpruritus is variable (Fig. 4). A pinnal-pedal scratchreflex is sometimes seen. Papules, scale, crusting,excoriations and secondary infections may be severe(Fig. 5). Dogs with lice often have a poor, dirty,matted coat although this can be associated withneglect as much as the lice themselves. Affected dogsmay also smell quite bad and are often irritable. Someanimals, however, are asymptomatic carriers.

Heavy infestations of sucking lice, especially in younganimals, may produce anaemia.

Mark Craig BVSc CertSAD MRCVSRE-FUR-ALL REFERRALS, 31 PORCHESTER ROAD, NEWBURY, BERKSHIRE, RG14 7QH

Louse infestation (pediculosis) in pet animals

Fig. 1: Trichodectes canis, the canine biting louse.

Fig. 2: Trichodectes canis nit.

Fig. 3: Scaling, crusting and alopecia on the pinna of aLabrador with lice.

ABSTRACT: Although pediculosis in pet animals is less common than flea infestation in most parts of the UnitedKingdom, it should be considered in the differential diagnosis of pruritus, erythema, scaling, anaemia andirritability. It is a cause of miliary dermatitis in cats. Lice are easily killed by many commercially availableinsecticides. Transmission is usually by direct contact but indirect transmission is also possible and brushes,combs, bedding and the general environment should be kept clean. DOI: 10.1111/j.2044-3862.2010.00027.x

Diagnosis

The diagnosis is suggested from the history andclinical signs but confirmation requires finding thelice. Lice are visible to the naked eye but biting lice move very quickly and may be difficult to see(Fig. 6). A magnifying glass may be helpful. Skin

scrapings, tape strips and hair plucks can be used todemonstrate both lice and nits (Fig. 7). Skin biopsiesare unnecessary, histopathology revealing varyingdegrees of superficial perivascular dermatitis.

The differential diagnosis includes allergic skindiseases, sarcoptic mange, cheyletiellosis and harvestmite infestation.

Prognosis

The prognosis is usually good with appropriatetreatment.

Treatment

Mats should be clipped and the patient and all in-contact dogs treated with an appropriate insecticide.Fortunately, lice are relatively easy to eradicatealthough products may need to be re-applied in linewith manufacturer’s instructions. Many of today’scommercially available insecticidal products areeffective and licensed for treating biting lice in dogs(Table 1). These products are considered effectiveagainst, but unlicensed for, sucking lice. Brushes,combs and bedding should be cleaned thoroughlyand the premises sprayed where appropriate with asuitable environmental insecticide (Table 2). Adviceshould be given to owners regarding importance ofgeneral hygiene and environmental cleanliness. Thesource of infestation should be investigated with aview to preventing re-contamination.

lICe IN CaTS

The species of louse found in cats is the biting louse,Felicola subrostratus. As well as being a cause of severepruritus, Felicola may be associated with miliarydermatitis. Cats may sometimes be asymptomaticcarriers of Felicola. Diagnosis is confirmed bydemonstration of lice or nits.

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Companion Animal Vol 16 March 201150 © 2011 Blackwell Publishing Ltd

Fig. 5: Erythema, alopecia and excoriations on theforelegs of the dog in Fig. 4.

Fig. 6: Lice and nits adherent to the base of hairs onthe head of a Labrador with Trichodectes infestation.

Fig. 7: Tape strips can be used to demonstrate lice inanimals.

Fig. 4: Depression, poor coat, scaling, crusting andalopecia in a Labrador with lice

Table 1: Commonly used insecticidal products, licensed for useagainst biting lice (Trichodectes canis) in dogs. all productsshould be used in line with manufacturer’s instructions.

Formulation Ingredients ApplicationAdvantage (Bayer plc) Spot-on Imidacloprid On dogAdvantix * (Bayer plc) Spot-on Imidacloprid and On dog

permethrinAdvocate (Bayer plc) Spot-on Imidacloprid, On dog

moxidectinEffipro Spray (Pfizer Ltd) Spray Fipronil On dogFrontline Spray (Merial Spray Fipronil On dogAnimal Health)Frontline Spot-on Dog Spot-on Fipronil On dog(Merial Animal Health)Frontline Combo Spot-on Fipronil, On dogSpot-on Dog methoprene(Merial Animal Health)Promeris duo Spot-on Metaflumizone, On dog(Pfizer Ltd) amitrazStronghold (Pfizer Ltd) Spot-on Selamectin On dog

* Contraindicated in cats Continued on page 52

Companion Animal Vol 16 March 201152 © 2011 Blackwell Publishing Ltd

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Treatment

Some insecticidal products are specifically licensedfor use against Felicola subrostratus in cats (Table 3).Advantix is toxic to cats and should always beavoided in this species. Cats should not be allowed tocome into contact with animals treated withAdvantix until the application site is dry. The datasheet states that cats should not be allowed to groomthe application site on a dog treated with Advantix.

lICe IN OTHeR SPeCIeS (Table 4)

Diagnosis is confirmed by demonstration of lice or nits.

GUINea PIGS

Lice are common in guinea pigs. The two mostcommon species, Gliricola porcelli (slender guinea piglouse) (Fig. 8) and Gyropus ovalis (oval guinea piglouse) are both biting lice. Another species of biting louse, more rarely found in guinea pigs, isTrimenopon hispidum.

Infestation in guinea pigs is often asymptomatic althoughpruritus, poor coat, scaling, crusting and alopecia,especially around the ears and dorsum, may develop(Fig. 9). Young guinea pigs kept in poor conditionsare more susceptible to heavy louse infestations.

Treatment

A recent study (Sanghun et al., 2008) suggested a singletopical application of 0.05 ml of a solution containingimidacloprid (10% w/v) and moxidectin (1% w/v)(Advocate spot on solution for small cats and ferrets:Bayer plc) to be an effective and convenient treatmentfor G. porcelli infestation in guinea pigs. Sprays

approved for lice in cats are likely to be safe andeffective in guinea pigs, although it would always beprudent to check with the manufacturers. A range oftopical and injectable ivermectin products areavailable for guinea pigs (Table 4).

RabbITS

Lice are an uncommon cause of skin disease inrabbits. Heavy infestations of Haemodipsus ventricosus(a sucking louse) may result in variable pruritus,scaling and anaemia.

For treatment options see Table 4.

Fig. 8: Gliricola porcelli, a biting louse of guinea pigs.

Table 2: Commonly used environmental insecticidal products.all products should be used in line with manufacturer’sinstructions.

Acclaim Spray S-methoprene, General, (CEVA Animal permethrin householdHealth Ltd) environmentIndorex Spray Permethrin, General, (Virbac Ltd) pyriproxyfen, household

piperonyl butoxide environmentRIP for fleas Spray Methoprene, General, (Genitrix) permethrin, household

bioallothrin environmentStaykil (Novartis) Spray Permethrin, General,

cyromazine householdenvironment

Table 3: Commonly used insecticidal products, licensed for useagainst biting lice (Felicola subrostratus) in cats. all productsshould be used in line with manufacturer’s instructions.

Formulation Ingredients ApplicationEffipro Spray (Pfizer Ltd) Spray Fipronil On catFrontline Spray Spray Fipronil On cat(Merial Animal Health)Frontline Spot-on Cat Spot-on Fipronil On cat(Merial Animal Health)Frontline Combo Spot-on Spot-on Fipronil, On catCat (Merial Animal Health) methopreneStronghold (Pfizer Ltd) Spot-on Selamectin On cat

Table 4: lice found in rabbits, guinea pigs, mice and rats andtreatments used.

Lice TreatmentRabbits Haemodipsus Pyrethroid-containing powders;

ventricosus permethrin (Xenex Ultra Spot-on,(sucking) Genitrix Ltd); ivermectin spot-on

(Xeno 50-mini, Genitrix); ivermectin spray (Xeno 200 spray, Genitrix Ltd); ivermectin injection (200-400 µg/kg sc injection on 3 occasions at 2 week intervals); selenium sulphide shampoo (Seleen, Ceva). Improved husbandry.

Guinea pigs Gliricola porcelli (biting) Imidacloprid and Gyropus ovalis (biting) moxidectin; also as Trimenopon hispidum per rabbits(biting)

Mice and ratsPolyplax serrata As per guinea pigs(sucking louse of mice)Polyplax spinulosa(sucking louse of rats)

Fig. 9: Alopecia in a guinea pig infested with Gliricolaporcelli, a biting louse.

8th International Parasite Control Symposium, Compendium of

continuing education for veterinarians, 29, 5A, May 2007.

BECK, W.: Common endo- and ectoparasitic diseases in small mammals

- clinical features, diagnosis and treatment: a review of the literature and

own experiences Tierarztl Prax 32(K):311-321, 2004.

SCARFF, D., Rabbits and rodents, In BSAVA Manual of Small Animal

Dermatology 2nd edition. Eds: Foster A and Foil C (2003) pp 242-251

Eds: Scott D.W., Miller M.H. and Griffin C.E. (2000) Muller and Kirk’s Small

Animal Dermatology 6th edition, pp 1415-1455. W.B. Saunders, Philadelphia.

mICE aND RaTS Sucking lice (Polyplax serrata in mice, Polyplaxspinulosa in rats) are occasionally found. Clinical signsare variable and include pruritus, erythema andscaling, typically on the neck and back. Young anddebilitated rodents are more susceptible.

TreatmentOne drop of imidacloprid (10% w/v) and moxidectin(1% w/v) (Advocate spot on solution for small catsand ferrets: Bayer plc) has been recommended fortreatment of lice in small rodents (Beck, 2004).

SummaryAlthough pediculosis in pet animals is less commonthan flea infestation in most parts of the UnitedKingdom, it should be considered in the differentialdiagnosis of pruritus, erythema, scaling, anaemia andirritability. It is a cause of miliary dermatitis in cats.Lice are easily killed by many commercially availableinsecticides. Transmission is usually by direct contactbut indirect transmission is also possible and brushes,combs, bedding and the general environment shouldbe kept clean.

FURTHER READING

GUAGUÈRE, E. and BEUGNET, F. In: A Practical Guide to Canine

Dermatology. Eds: Guaguère E., Prélaud P. and Craig J.M. (2008) pp 203-

204, Kalianxis, Italy.

SANG-HUN KIM HYUNG-KYOU JUN, MYUNG-JO YOO and DUCK-

HWAN KIM. Use of a formulation containing imidacloprid and

moxidectin in the treatment of lice infestation in guinea pigs. Veterinary

Dermatology, 2008, 19, 3, 187-188.

C O N T I N U I N G P RO F E S S I O N a LD E v E L O P mE N T S P O N S O R E D b Yb aY E R a N I ma L H E a LT H

1. Which of the following statements is/are accurate:a. Lice are small, flattened insectsb. Lice spend much of their life cycle off the hostc. Lice are not host-specificd. All of the above

2. Linognathus setosus is the sucking louse of dogs:True or false.

3. Which of the following are biting lice:a. Felicola subrostratusb. Linognathus setosusc. Polyplax serratad. All of the above

4. Which of the following lice are found in guinea pigs:a. Gliricola porcellib. Polyplax serratac. Heterodoxus spinigerd. None of the above

These multiple choice questions are based on the abovetext. Answers appear as supporting information in theonline version of this article.

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louse infestation (pediculosis) in pet animals

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