Lice are external parasites fairly uncommon on pets in the U.S. Two types take up residence on dogs: the canine chewing louse, Trichodectes canis, which consumes its host's skin, and the canine sucking louse, Linognathus setosus, which feeds on its host's blood. They're most likely to become a problem in dirty, unsanitary conditions. Lice require a host to live, but they can survive for a while if they fall off or cannot locate a host right away.
Life Without a Host
Lice securely adhere their eggs, or nits, to hair shafts on their host. However, once hatched, nymphal and adult lice sometimes fall off their host or get knocked off by the host's scratching. Lice don't quickly die without a host, though, and generally survive for three to seven days on their own. The species, age, environmental factors, when they last fed and other specifics can affect exactly how long a louse is able to live off of a host. Because they survive for at least a few days without a host, aggressive environmental cleaning is important during treatment and containment phases if you have a lice infestation in your home.
Seeking a Host
Lice that have fallen off or been dislodged from their host will eagerly seek out a new host on which to feed. However, unlike fleas, ticks and other common ectoparasites, lice are highly species-specific. In other words, dog lice only go on dogs to feed and reproduce; cat lice stick to cats, human lice stick to humans and so on. So, if your dog has lice, you only need to worry about her becoming reinfested and about any other dogs in the home becoming infested. Other animals and people need not be quarantined or treated.
See your vet for lice treatment. He'll probably prescribe an appropriate topical insecticide, usually one made for flea control. These come in a number of forms, including shampoos, sprays and powders. Lice are generally easy to kill off, but their nits aren't susceptible to most insecticides. For this reason, one or two subsequent treatments are typically prescribed every one or two weeks to eliminate new lice that hatch after the initial treatment.
Because lice are likely to fall off your dog and survive for up to a week, environmental cleaning is a necessary aspect of controlling an infestation until completion of the prescribed medication regimen. Launder your dog's bedding and wash her toys and grooming implements every day or two. Vacuum the floors, carpets and furniture every day or two, as well, and carefully empty the vacuum bag outside and deposit it contents into a sealed garbage bag in an outdoor garbage can. Disinfect your dog's living space with a pet-safe cleaning product. Items of concern that can't be washed can be stored in airtight bags for a few weeks to kill off any lice and nits.