Lice are tiny, species-specific external parasites that live on the skin and hair coat of dogs and other mammals. A single one of these parasites is called a "louse." Adult canine lice are pale, wingless and flat. They are small insects, averaging between 1.5 to 4 millimeters in length. Usually, they can be seen by the naked eye, although it is easier to identify them under a microscope or magnifying glass. Lice live for about 4 weeks. The eggs (called "nits") transition to 3 different stages of nymphs, and then become adults.
Lice are classified in the order Phthiraptera. They are generally divided into two distinct categories: biting lice (suborder Mallophaga) and sucking lice (suborder Anoplura). There are two main species of lice that infest dogs. The canine biting louse is Trichodectes canis. The sucking louse of dogs is Linognathus setosus. A heavy louse infestation, whether caused by biting lice or sucking lice, is referred to as "pediculosis." The lice that affect people are not the same as the lice that affect dogs or other animals, and they typically do not transfer between different species. In other words, people cannot become infested with lice from their dogs, and dogs become infested with lice from their people.
Lice are annoying insects. Fortunately, they are not common in clean, healthy, well-fed and well-maintained companion dogs. These parasites tend to thrive mostly on debilitated dogs that are old, run-down, malnourished or poorly cared for. When lice are present, they usually are found in dirty areas under matted hair around the dog's head, ears, neck, shoulders and genitalia. Lice cause intense itchiness, constant irritation and relentless restlessness in affected dogs. This almost always causes the dogs to lick, rub, scratch, chew and bite at affected areas. They also develop a coarse, roughened hair coat and skin redness, rawness and inflammation (dermatitis). Some dogs become lethargic, lose weight and suffer poor growth. Owners of dogs infested with lice may notice bare patches of skin, where the hair has been rubbed off as a result of the discomfort caused by these parasites. These symptoms usually are worse when sucking lice are involved.
Dogs that are heavily infested with sucking lice may develop mild to severe anemia, because those lice feed on and will deplete the dogs of blood, proteins and other essential nutrients. Anemia is an abnormal reduction in the number of circulating red blood cells. Red blood cells are necessary to deliver oxygen and other key nutrients throughout the body, and to remove waste products from all tissues. Dogs that are severely anemic, whether from sucking lice, ticks, internal parasites or otherwise, may require intravenous blood transfusions or supplementation with iron, vitamins and other minerals.
Sucking lice are slow-moving external parasites; in fact, most of the time they are virtually motionless. Biting lice, on the other hand, tend to move more quickly, although they still are considered to be slow-movers. Biting lice feed on the flakes and scales of a dog's skin, not on its blood, and they usually are less irritating than sucking lice. Unlike fleas, lice do not jump from one dog to another. However, they can be spread by direct physical dog-to-dog contact. This can happen anywhere, but it most commonly occurs in boarding kennels, animal shelters, grooming facilities, dog parks and other situations where a number of dogs are in close proximity. Dogs that share bedding, crates or runs with unfamiliar dogs have an increased risk of becoming infected with lice.
A diagnosis of pediculosis (louse infestation) is usually made when an owner, groomer or veterinarian visually identifies adult lice or their eggs, which are called "nits," on a dog - especially in soiled areas under matted hair. Adult lice look more like specks of dirt than insects. They can be difficult to detect when only a few are present. However, they typically are easy to see when there is significant infestation. Adult lice tend to stick to a dog's skin, rather than to its hair. On the other hand, nits - which look like grains of white sand - do stick to a dog's hair, especially at the base of the hair shaft. Sometimes, louse nits look like flakes of dandruff that closely resemble Cheyletiella mites (so-called "walking dandruff"). When these insects are examined under a microscope or magnifying glass, the differences between them become readily apparent.
Because lice cannot survive for long off of their particular host, they are almost never found living freely in the environment. This distinguishes them from fleas, ticks and most other external dog parasites. Lice are one of the easiest of all canine parasites to treat. They are easily killed by topical insecticides. Some of the more common insecticides used to treat pediculosis include lime-sulfur, pyrethrins and pyrethroids. Many authorities recommend that the infested dog, and all other dogs that it has been in close contact with, be treated every 1 to 2 weeks, for at least 4 weeks, with an insecticidal shampoo, dip or powder. A number of canine flea-control products are reportedly effective at killing or preventing infestation of lice. However, some insecticides and preventatives are not recommended for use in or on pregnant bitches or young puppies. Bedding that was used by an infected animal probably should be disposed of in an outside garbage receptacle. Alternatively, owners can try to disinfect and sanitize the dog's bedding, along with its sleeping area, grooming equipment, leashes, collars and any other areas that it frequented. A veterinarian is in the best position to advise owners about the appropriate methods to prevent and to treat canine lice.