CAPC Recommendations:
Ectoparasites:
Lice
Species
Trichodectes canis (canine chewing louse)Felicola subrostratus (feline chewing louse)
Linognathus setosus (canine sucking louse)
Trichodectes canis is a chewing louse found on dogs and wild canids throughout the world and is a vector of the dog tapeworm, Dipylidium caninum. Trichodectes canis causes little irritation except in heavy infestations. It does not occur on kennel-reared dogs except under conditions that likely are unsatisfactory in many other ways.
Felicola subrostratus, a chewing louse, is usually found in large numbers only on aged or diseased cats and on some wild felids. It is probably cosmopolitan in location. Infestations often go unnoticed.
Linognathus setosus is a sucking louse occasionally found on the dog (particularly on long-haired breeds) throughout the world. It causes little irritation except in heavy infestations and is usually absent from dogs raised in kennels. This louse has also been found on wild canids.
Overview of Life Cycle
- A female lays several eggs daily throughout her life, which is about 30 days. Eggs are cemented near the base of the hair and hatch in one to two weeks.
- Hatching of the eggs is followed by three nymphal stages that molt three times and develop into mature lice in two to three weeks. The complete life cycle requires three to six weeks.
- The chewing lice, T. canis and F. subrostratus, feed on tissue debris; the sucking louse, L. setosus, feeds on blood in a sucking manner like a mosquito.
- Lice can survive only three to seven days if separated from the host.
Stages (see images on right)
- Adults (1 to 2.5 mm in length) are yellowish to tan with dark markings.
- In both of the chewing lice, the heads are wider than the thoraxes; the head of F. subrostratus also has a characteristic triangular anterior end.
- In L. setosus, the head is narrower than the thorax. The antennae are short, stout, three-segmented, and fully exposed. Each leg has only one claw. The abdomen is oval and has six pairs of spiracles on the lateral edges of each abdominal segment.
- Eggs (nits) are operculate and glued to the hair shafts.
Disease
- Chewing lice are attached by their claws or mandibles to the base of a hair, usually on the head, neck, and tail. Louse concentrations may occur near body openings or skin abrasions where the lice are seeking moisture.
- Sucking lice are found primarily on the neck and shoulders, especially under a collar.
- Usual signs of louse infestation are irritation, rubbing, scratching, and biting of infested areas, along with sleeplessness, nervousness, alopecia, and a rough matted coat. Heavy infestations may cause restlessness, pruritus, scratching, a ruffled coat, and sometimes alopecia.
Prevalence
- Infestations are more prevalent in very young, old, or debilitated animals or animals maintained in unsanitary environments.
- The chewing louse is fairly common on dogs and cats around the world. Another chewing louse, Heterodoxus spini, is found on dogs in such tropical areas as the Philippines.
- Infestations with the sucking louse are most common in the colder climates to which this louse is mainly restricted.
Host Associations and Transmission Between Hosts
- These lice are fairly restricted parasites of dogs and cats. They usually are not shared between dogs and cats and are not transmitted from pets to people.
- Transmission between hosts is usually through direct contact, but transmission can also occur via eggs on brushes, combs, or similar grooming equipment. The eggs and other stages will die due to desiccation if kept for several hours under hot dry conditions such as in a clothes drier.
Prepatent Period and Environmental Factors
- Adults become mature about three weeks after hatching. Infestations generally are most common when animals are held under unsanitary conditions and during the cooler months.
Site of Infection and Pathogenesis
- Effects on the hair or skin are usually minimal to nonexistent. The eggs and nits can be seen on the hair and may give it a scruffy appearance.
- Cats can develop heavy infestations resulting in restlessness, pruritus, scratching, a ruffled coat, and sometimes alopecia.
Diagnosis
- Diagnosis is based on clinical signs and on demonstration of the parasite or its eggs.
Treatment
- Infestations have been relatively easy to treat for many years. Fipronil (both spray and spot-on formulations) is labeled for the treatment of louse-infested cats and may work for dogs. Imidacloprid and selamectin administered according to label instructions for flea control are also effective. Topical permethrin can be used on dogs with good effect.
- Treated animals should be placed in a clean, disinfected cage or living space. Treatment may be repeated in a week to ensure that any nymphs hatching from eggs are also killed.
Control and Prevention
- Newly acquired dogs should be examined and treated if infested. Infested pets should be quarantined and treated before coming into contact with other pets.
- Monthly treatment with fipronil, imidacloprid, or selamectin for control of fleas should also control lice.
Public Health Considerations
- These parasites pose no public health risk.
- Rarely, T. canis has been reported as a source of cysticercoids of D. caninum that could infect humans or dogs and cats that happen to ingest infected lice.
