Lice Life Stages
Pediculus humanus var. corporis, from left to right: three nymphal-staged lice, stage N1, N2, and N3; an adult male louse; and an adult female louse. Photo courtesy of CDC
Lice are an uncommon parasite in dogs and cats in the U.S. Lice infestations can occur in animals in any environment, but they're more common in animals that live in crowded conditions, in animals that aren't observed as closely or often, etc. (Frequent, close examination of the animal's skin and hair helps prevent one louse from having the opportunity to turn into an infestation.) Lice are host-specific. Human lice affect only humans. Dog lice affect dogs. Cat lice affect cats. Rarely, a dog or cat louse might end up on a human, but it doesn't stay there. Children who have head lice get them from other humans.
Lice are flat, six-legged, wingless insects that can be seen with the naked eye. (This makes diagnosis easy.) Lice don't move much or quickly. They spend their entire 21-day life cycle on a pet. They lay eggs, which are called nits, on the shafts of the hair. Nits are easy to see. They attach only to the pet's hair and look like white flakes on the hair shaft.
There are two kinds of dog lice. One (Trichodectes canis) chews skin; the other (Linognathus setosus) sucks blood. The bloodsuckers cause more skin irritation than the chewers do because they break the skin.
There is one kind of louse (Felicola subrostrata, a chewing louse) that affects cats.
Photo courtesy of CDC
What you will notice with either type of louse is severe itching and a scruffy dry coat with bald patches. Lice generally congregate around the ears, neck, shoulders, and anus, so those areas will be most affected.
Because puppies have a small volume of blood compared to adults, they are more likely to become anemic as a result of the blood-sucking lice. In severe cases, a dog could lose about one-fourth of his blood to lice within a few months, and end up anemic or in shock.
Both types of dog and cat lice are transmitted by direct contact with an infested dog or cat, or by contact with nit-contaminated grooming equipment, bedding, etc.
Your veterinarian can diagnose a louse infestation just by looking at your pet.
Treatment and Prevention
Lice are usually fairly easy to eliminate because they haven't yet built up any resistance to insecticides.
There are multiple treatment options your veterinarian may employ. The veterinary clinic employees may bathe your dog with an insecticide shampoo to quickly eliminate the adult lice, and then use an insecticide spray or powder to continue the job. They may use fipronil, selamectin, or an isoxazoline (sarolaner, lotilaner, fluralaner, and afoxalaner.) Whatever treatment is used, the treatment may need to be repeated to kill lice that have hatched from the eggs. Commonly, the pet will be treated every two weeks for three to four treatments. (The isoxazoline products may need only 1-2 treatments.) However, in some cases, treatments may be needed every week for two to four treatments. If your pet continues to have louse infestations after that point, your veterinarian may switch to another treatment.
If the coat is matted, the matted areas (or even the entire pet) should be shaved.
Clean grooming equipment after every animal. Places that have larger turnover, such as rescues, shelters, and boarding kennels, may encounter more animals that carry lice so sanitation is particularly important.
Dispose of or wash bedding.
Although it's not usually necessary to use a fogger for environmental control of lice, it might be needed in a severe infestation.