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These external parasites are becoming increasingly rare and are species specific. They are usually 1-2 mm in length, a faun to plum colour, and will cause intense irritation on all body surfaces, especially over the body where areas of hair loss and skin inflammation may occur.

Lice Infestation

Lice are insects that can be seen with the naked eye. They are flattened and possess no wings. They are very host-specific and do not tend to leave their preferred animal, in this case dogs and puppies. Lice spend their entire life cycle on the pet. There are several kinds of lice. Blood-sucking lice belong to the group Anoplura. Those that do not suck blood, but rather chew skin, are grouped as Mallophaga.

Transmission of lice is by direct contact with an infested pet. Unlike fleas and ticks, lice do not persist or travel in the environment. Grooming instruments may, however, serve as a source of transmission.

Lice lay eggs (termed nits) on the hair shafts. The life cycle takes about 21 days to complete.

Trichodectes canis is the biting louse of dogs. Another commonly found biting louse of the canine is Heterodoxus spiniger. The only sucking louse of the dog is Linognathus setosus. Cats have one biting louse and that is Felicola subrostratus. None of these lice present a problem to humans.

The most noted sign of a louse infestation is a scruffy, dry hair coat. Hair loss may occur and the animal may itch, at times severely. In very heavy infestations of blood-sucking lice (biting), one may detect anaemia, especially in puppies. A diagnosis can usually be accomplished with the naked eye. Nits tend to be more visible than the actual louse, but both can be seen.

Treatment is very simple. Both biting and chewing lice are easily killed with flea and tick products. We prefer to bathe weekly with a pyrethrin shampoo. Once the pet is dry, powder heavily with a flea and tick powder. Repeat this process weekly for four weeks. It usually is not necessary to treat the environment, but flea and tick foggers may help, especially in severe cases. Keep all grooming utensils clean.

Of all the parasites of dogs and cats, lice are the easiest to eliminate, and they pose no threat to you or your children. 

Canine Biting Louse Trichodectes canis

In the wingless insect suborder of chewing lice (Mallophaga), Trichodectes canis is the louse species that most commonly feeds on domestic dogs and other canids such as coyotes, wolves, and foxes that often have contact dogs. Unlike ticks and other parasites, the 2,800 species of biting lice described worldwide are very host specific. The dog louse or canine biting louse is about 1.5 millimeters in length with a dorsoventrally flattened body and a broad, flat head. As representatives of the Isonocera group, chewing lice extend their highly visible trisegmented antennae laterally. Each of the three pairs of legs is armed with a strong claw for digging into the host canid, even in the face of frantic biting and scratching.

T. canis should not be confused with the canine sucking louse, Linognathus setosus, which features a short, blunt head and seeks blood meals on dogs and their relatives. Rather than needle-like mouthparts that pierce skin, chewing lice, as their names imply, have large, opposing mandibles used to feed on hair fragments, skin, and blood. Symbiotic bacteria, found in specialized mycetocytes throughout the insect's fat reserves, are required for digestion. When the insects are deprived of their bacteria, they perish within a few days.

Having a life cycle that takes about three to four weeks, canine biting lice can be found anywhere on the dog's body. Although rarely discovered on healthy animals, poorly nourished dogs may have heavy infestations, adding to their troubles. In addition to causing severe itching and loss of sleep, Trichodectes canis can also act as the intermediate host for the dog tapeworm, Dipylidium caninum. In the case of Alaskan wolf packs infected by pets, extensive hair loss in sub-zero temperatures creates metabolic demands that reduce survival rates.

Females lay up to 100 eggs or nits. The nits of the canine biting louse are protected by an operculum and are cemented to the base of the dog's hairs. When the eggs hatch, the operculum is lost and the larva emerges through an opening. Because the entire 20-day louse life cycle is spent on the hosts, louse control primarily involves isolating and treating infested dogs with insecticides. There is no need to treat indoor carpet or backyard soils and vegetation as required with other canine pests, such as fleas and ticks. Often, adding additional Vitamin B to the dog's diet helps fight these infestations.

Contributing Authors
Cynthia D. Kelly, Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.


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