Lice infestation can occur in debilitated or stray dogs and cats, but is rare in populations treated with monthly flea and tick preventatives. As is true for other species, pruritus, self-trauma and roughened haircoat are common clinical signs. Pyrethrins can be used to treat dogs with lice; fipronil and selamectin are common spot-on treatments used for both dogs and cats.
Courtesy of Dr. Jennifer Ketzis.
Courtesy of Dr. Jennifer Ketzis.
Dogs can be infested with one species of bloodsucking lice (Linognathus setosus) and two species of chewing lice (Trichodectes canis and Heterodoxus spiniger).
Dogs neglected or in poor health may become heavily infested with L setosus, which tends to prefer long-haired breeds.
T canis prefers the head, neck, and tail of the host, and it may be found around wounds and body openings. Very heavy infestations can lead to severe anemia.
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.
Lice infestations of dogs 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. Infestations can sometimes go unnoticed in long-haired breeds, requiring the parting of hair to find nits and lice.
Courtesy of Dr. Jennifer Ketzis.
Courtesy of Dr. Jennifer Ketzis.
Cats can be infested with one species of chewing louse (Felicola subrostratus); however, there are rare reports of H spiniger on feral cats in some regions of the world. The louse may be more common on older, long-haired cats that are unable to groom themselves.
Veterinarians 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 infestations resulted 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 US. Infestation usually occurs on debilitated, feral, stray, or shelter animals.
Pathogenesis and Disease Transmission of Lice in Dogs and Cats
T canis can serve as an intermediate host to the double-pored tapeworm, Dipylidium caninum. This parasite of dogs and cats can occasionally infect humans. Heterodoxus spiniger has been found to contain the filarial nematode Acanthocheilonema (formerly Dipetalonema) reconditum; however, its competence as a vector has not been demonstrated.
Treatment of Lice in Dogs and Cats
Monthly flea and tick products with protection against lice
In severe infestations, clipping of the hair
Various 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. Other compounds, such as fluralaner and moxidectin, also have demonstrated efficacy against lice on dogs; however, they are not currently registered for this use in the US.
Although carbamates are effective against lice, carbaryl-containing collars were removed from the US market in 2010, and propoxur-containing collars were removed in 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 also 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.
Key Points
Lice infestations on dogs and cats can lead to severe dermal irritation, alopecia, and anemia.
Infestations are frequently associated with underlying conditions.
Many flea and tick products are effective in controlling lice on dogs and cats.
For More Information
Martins DB, de Oliveira EZ, Valandro MA, et al. Trichodectes canis in puppy and adult dogs. Comp Clin Pathol. 2014;23:1485-1489.
Bowman DD. Feline Clinical Parasitology. 1st ed. Iowa State University Press; 2002.
Also see pet health content regarding lice of dogs and of cats.
