Lice Notes

Ectoparasitic skin disease - lice

INTRODUCTION

Lice are insects, and therefore have three body segments and three pairs of legs. They are small but visible to the naked eye.

N.B. lice may be confused with keds, which are wingless flies. Keds are larger than lice and have much longer legs.

Lice may be sucking or chewing lice. Sucking lice have long narrow heads, whereas chewing lice have broader heads.

Sucking louse Chewing louse

Lice are very host specific.

Lice infestation is known as pediculosis.

The louse life cycle lasts approximately 3 weeks.

Lice eggs are found attached to hairs, and can cause indirect infestation from contaminated bedding and blankets.

CANINE AND FELINE PEDICULOSIS

In dogs caused by Trichodectes canis (biting louse) and Linognathus setosus (sucking louse).

Trichodectes canis Linognathus setosus

In cats caused by Felicola subrostratus.

Clinical signs

• May be asymptomatic

• Poor haircoat

• Scaling

• Papules

• Crusts

• Variable pruritus.

• Heavy infestation can cause anaemia and lethargy.

Pathogenesis

• Lice eggs are found attached to hairs.

Diagnosis

• Demonstration of lice or lice eggs with magnifying glass or under microscope

• Tape strip

• Hair plucking

Treatment

• Insecticidal products, but these are often poorly ovicidal. Treatment should be re-applied every 2 weeks for 4-6 weeks.

• Imidacloprid/moxidectin

• Fipronil

• Amitraz

• Selamectin

• Environmental cleaning.

Prognosis

• Good.

EQUINE PEDICULOSIS

Caused by Werneckiella equi (biting louse, previously Damalinia equi) and Haematopinus asini (sucking louse).

Werneckiella equi Haematopinus asini

Clinical signs

• Variable hair loss

• Broken hairs

• Excoriation

• Scaling

• Mature lice and eggs visible to naked eye

• Particularly under the main, tail and forelock.

Pathogenesis

• Entire life cycle is spent on the horse.

• Transmission may direct or indirect.

• Pediculosis is highly contagious.

• The lice can survive off the host for up to 4 weeks depending on environmental conditions.

• Pediculosis is more common in autumn and winter.

• It is associated with animals that are stressed, diseases, under nourished or living n overcrowded spaces.

Diagnosis

• Identification under a microscope

• Tape strips

• Coat brushings

Treatment

• Topical insecticides – three treatments t 10 day intervals.

• Kill adults but are poorly ovicidal.

• Permethrin (Switch, Cooper’s fly repellent plus)

• Cypermethrin (Deosect)

• Piperonylbutoxide and pyrethrum (Dermoline shampoo).

• Treat all in contact animals.

• Rugs should be steam cleaned and treat environment with louse powders.

Prognosis

• Good.

BOVINE AND OVINE PEDICULOSIS

In cattle caused by Bovicola bovis (biting louse), Linognathus vituli (sucking louse), Solenoptes capillatus (sucking louse) and Haematopinus eurysternus (sucking louse).

Bovicola bovis Solenoptes capillatus

Linognathus vituli Haematopinus eurysternus

In sheep caused by Bovicola ovis (biting louse), Linognathus pedalis (sucking louse) and Linognathus ovillus (sucking louse).

Bovicola ovis

Linognathus pedalis Linognathus ovillus

Clinical signs

• Pruritus

• Scractching

• Rubbing

• Chewing

• Rough coat

• Decreased production

• Alopecia

Pathogenesis

• ...

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