Pediculosis

Lice infestation is uncommon in dogs and cats. They complete their life cycle on the host within 14 to 21 days. Lice can survive off the host for only a few days. They are spread by direct contact or by contaminated brushes, combs, and bedding. The white eggs, or nits, are cemented firmly to the hairs of the host. The following lice species cause pediculosis in dogs: Trichodectes canis (biting lice), Heterodoxus spiniger (biting lice); Linognathus setosus (sucking lice).

Courtesy of National Science Foundation

Sucking Lice

Sucking lice (Linognathus setosus) have mouthparts adapted for sucking blood of the host. With heavy infestation, they produce sufficient anemia to cause weakness, and some animals become distraught and ill-tempered because of the chronic skin irritation. Sucking lice do not move and are easily seen and caught.²

Trichodectes canis and Heterodoxus spiniger are called biting lice which feed on skin debris and hair, but some species have also mouthparts adapted for drawing blood from their hosts. Biting lice move rapidly and may be difficult to find and capture. Because they are active, they may cause more irritation than sucking lice, and rubbing by their host can cause alopecia. Trichodectes canis is the common biting louse of dogs; it may act as the intermediate host of the dog tapeworm.²

Signs of Pediculosis

Clinical signs are variable. Animals can have no clinical signs and be parasite carriers. There may be minor skin inflammation only, alopecia only, pimples and crusting eruptions, anemia, weight loss and intense itch.¹ Lice usually accumulate under mats of hair and around the ears and body openings.² Lice produce few lesions, but secondary dermatitis from scratching may be severe. Pediculosis may look like flea allergy dermatitis.²

Parasiticidal dips, powders or shampoos are used once weekly for 4 weeks. Frontline flea spray is applied twice 2 weeks apart. Ivermectin may be prescribed for sucking lice as for cheyletiellosis. The premises must be cleaned up: wash bedding, brushes, and combs. Treat all affected animals and other animals in close association with them.

References

1. Scott, Miller, Griffin. Parasitic Skin Diseases.
2. George H. Muller, Danny W. Scott, Robert Warren Kirk, William Howard Miller, Craig E. Griffin. Muller & Kirk's small animal dermatology.

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