Dogs can be infested with one species of bloodsucking lice, Linognathus setosus, and two species of chewing lice, Trichodectes canis and Heterodoxus spiniger. H spiniger is considered rare in North America. It is distributed worldwide but appears to be more common in warmer environments; infestations are heavier on animals in poor physical condition. H spiniger exhibits atypical behavior for a chewing louse—it is a blood-feeder. Dogs neglected or in poor health may become heavily infested with L setosus, which tends to prefer longhaired breeds. T canis prefers the head, neck, and tail of the host, and it may be found around wounds and body openings. Infestations may be heavy on very young and very old animals. Infested dogs rub, bite, and scratch the affected area and have a rough, matted coat.
Cats can be infested with one species of chewing lice, Felicola subrostratus, although there are rare reports of H spiniger on feral cats in other regions of the world. The louse may be seen more frequently on older, longhaired cats that are unable to groom themselves.
Practitioners should be able to distinguish Phthirus pubis, the human crab louse, from the lice of dogs and cats. This species may be presented for identification by owners who claim to have found them on an animal. P pubis does not typically infest dogs or cats; there have been only two reports of dogs infested with P pubis, both of which occurred from sharing bedding with a person who was severely infested.
With widespread use of monthly flea and tick preventives, pediculosis in dogs and cats has become rare in the USA. Infestation is usually seen on debilitated, feral, stray, or shelter animals.
T canis can serve as an intermediate host to the double-pored tapeworm, Dipylidium caninum. This parasite of dogs and cats can occasionally infect people. H spiniger has been found to contain the filarial nematode Acanthocheilonema reconditum (formerly Dipetalonema reconditum), but its competence as a vector has not been demonstrated.
A variety of compounds effectively control lice on dogs and cats, including many of the topical, monthly flea and tick control products. Pyrethrins and pyrethroids are very effective pediculicides. However, caution must be exercised when using these products on cats, because this species is highly sensitive to pyrethrins and pyrethroids, lacking the ability to metabolize high doses. Limited pyrethrin or pyrethrin products are labeled for use on cats; the products either contain very low concentrations of the active compound or are available in a slow-release formulation (eg, flumethrin/imidacloprid collar). Selamectin, imidacloprid, and fipronil have all been used successfully to treat lice on dogs and cats.
Although carbamates are effective against lice, carbaryl-containing collars were removed from the USA market in 2010, and propoxur-containing collars will no longer be available for sale in the USA after April 1, 2016. Extra-label use of eprinomectin or doramectin may result in fatalities.
Currently, spot-on products are the most popular way to treat lice in dogs and cats. However, other formulations, such as collars, shampoos, sprays, or dusts, are available for insect control on pets.
If the animal is heavily matted or long-haired, treatment may be facilitated by clipping the coat. Bedding should be washed frequently in hot, soapy water or treated with an approved bedding or premise spray until the infestation is controlled. Certain fipronil products are labeled for this use. Nutritional deficiencies or concurrent health conditions should be addressed.