Lice are small, flightless insects that live in the hair or feathers of animals and people. There are 2 basic types of lice. Biting or chewing lice (order Mallophaga) infest both birds and mammals. They feed mostly on skin debris and the secretions of their hosts. Blood-sucking lice (order Anoplura) are skin parasites of mammals only. Typically, lice are species specific; that is, they do not readily transfer from one animal species to another.
Female lice glue their eggs, called nits, to the hairs of the host near the skin. Ordinary shampooing and washing will not dislodge the nits. Nits are pale, translucent, and almost oval in shape. Once the nits hatch, the lice undergo a nymphal stage before reaching adulthood. The immature nymphs look very much like adult lice, only smaller. It takes about 3 to 4 weeks for most lice to go from nit to reproductively capable adult, although this period varies with the species.
Dogs can be infested with 2 species of lice, Linognathus setosus (the dog sucking louse) and Heterodoxus spiniger (the biting louse). Dogs in poor health can become heavily infested. The biting louse is rare in North America. It can serve as an intermediate host for intestinal tapeworms (see Digestive Disorders of Dogs: Tapeworms).
The first signs that your dog may have lice include scratching, biting, and rubbing of infested areas. A dog with lice will have a rough, dry coat. If the lice are abundant, the hair might also be matted. Sucking lice cause small wounds that can become infected. Usually, the diagnosis is made by seeing lice on the infested pet. Parting the hair often reveals the lice. Chewing lice are active and can be seen moving through the hair. Sucking lice usually move more slowly. They are often found with their mouth-parts embedded in the skin.
Using a fine-toothed comb to dislodge nits is a tedious process that will not kill lice that have hatched. Dogs, cats, and other pets are usually treated with dips, washes, sprays, or dusts that kill lice. Your veterinarian can recommend an appropriate control product for your pet and provide directions for its use.
Lice dropped or pulled from the host die in a few days, but eggs may continue to hatch over 2 to 3 weeks. Thus, lice control treatments should be repeated 7 to 10 days after the first treatment (see Drugs and Vaccines: Antiparasitic Drugs). Careful inspection of your pet's coat should be continued daily for at least 2 weeks after you see the last louse. Be sure to carefully collect any lice (dead or alive) removed from your pet and dispose of them promptly in a sealed container (such as a zip-closure plastic bag).
In severe louse infestations, the dog may damage its skin by scratching. Bacterial infections and scratch wounds are common. If these conditions are present, your veterinarian may prescribe an antibiotic or other medication.
In addition to killing the lice on your pet, you will want to be sure that lice are not infesting your dog's bedding, collar, grooming tools (including bushes or combs), and other similar objects in your dog's environment. Careful cleaning and inspection of these objects can help provide your pet with continued relief from the irritation caused by lice.
The lice that infest dogs, cats, and other pets are not normally attracted to humans. Therefore, while care in dealing with the lice infecting your pet is recommended, owners should understand that people rarely get lice from their pets.
Last full review/revision July 2011 by Karen A. Moriello, DVM, DACVD; Patricia D. White, DVM, MS, DACVD; Michael W. Dryden, DVM, PhD; Carol S. Foil, DVM, MS, DACVD; William W. Hawkins, BS, DVM; Thomas R. Klei, PhD; John E. Lloyd, BS, PhD; Bernard Mignon, DVM, PhD, DEVPC; Wayne Rosenkrantz, DVM, DACVD; David Stiller, MS, PhD; Patricia A. Talcott, MS, DVM, PhD, DABVT; Alice Villalobos, DVM, DPNAP; Stephen D. White, DVM, DACVD