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3.13 Pediculosis (Louse infestation) – Small Animals

Learning Objectives

  1. Learn the host specificity of lice.
  2. Learn the approximate time that lice can live off the host.
  3. Learn the types of louse that infests cats and dogs.
  4. Know the methods to identify lice.
  5. Know the clinical signs associated with louse infestation.
  6. Know how to manage louse infestation.

  1. General Considerations:

    1. Louse infestation also known as pediculosis is uncommon in dogs and cats.
    2. Lice are highly host-specific.
    3. They complete the life cycle on the host in 14 to 21 days.
    4. The female louse lives for about 30 days and lays several eggs daily throughout her life.
    5. Lice survive off the host for only about 3 to 7 days.
    6. In low infestation, lice cause minimal to no clinical signs.
    7. Contagion occurs by direct contact with the infested animal of the same species or by contaminated brushes, combs, and bedding.
    8. The operculated eggs (nits) are cemented firmly to hair shafts of the host.

  2. Cause:

    1. Dogs:
      1. Trichodectes canis: biting or chewing louse (suborder Mallophaga). Vector of the dog tapeworm (Dipylidium caninum).
      2. Heterodoxus spiniger: biting or chewing louse (suborder Mallopaga).
      3. Linognathus setosus: sucking louse (suborder Anoplura). Rare cause of pediculosis in dogs.
    2. Cats:
      1. Felicola subrostratus: biting or chewing louse (suborder Mallophaga).

  3. Clinical Signs:

    1. Clinical signs are variable and depend on the degree and duration of infestation.
    2. Animals can be asymptomatic carriers.
    3. Clinical signs if present include variable degrees of pruritus, self-inflicted alopecia, variable degrees of inflammation and scaling and a rough matted hair coat. Papules and crusting may occur occasionally.
    4. Anemia can develop in heavy and chronic infestation with the sucking louse Linognathus setosus.

  4. Diagnosis:

    1. Demonstration of lice and/or eggs on physical examination.
    2. Scotch tape impression is the best method to immobilize and demonstrate the lice.

  5. Treatment:

    1. Correct any underlying disease or factor.
    2. Matted hairs should be clipped before the application of topical parasiticides.
    3. Fluralaner (Bravecto®), afoxolaner (NexGard®) and esafoxolaner (NexGard Combo®) have shown to be effective to treat louse infestation in cats and dogs caused by sucking and chewing lice. The label dose recommended to control flea and tick was used in the studies.
    4. Fipronil (Frontline® flea spray; Merial): Apply twice 2 weeks apart. Fipronil is also available for dogs and cats as a spot-on and to be applied once monthly (Frontline® Plus; Merial).
    5. Selamectin (Revolution®; Zoetis) applied once or twice a month is effective.
    6. Imidacloprid is available in several products (Advantage II®, Advantage Multi®, K9 Advantix II®; Bayer HealthCare LLC.). If applied once or twice a month it should be effective.
    7. Seresto™ flea and tick collar (Bayer HealthCare LLC; Shawnee Mission, KS) is available for both cats and dogs and kills lice. It is labeled for dogs and puppies 7 weeks of age and older and for cats and kittens 10 weeks of age and older.
    8. Ivermectin at the dose of 300 µg/kg (0.3 mg/kg) given subcutaneously every 2 weeks for three treatments is effective to treat the sucking louse Linognathus setosus.
    9. Clean-up the environment and fomites by washing beds, brushes, and combs.
    10. Treat all in-contact animals of the same species.

Important Facts

  • Lice infestation is uncommon in dogs and cats.
  • Cats are only infested by the biting louse Felicola subrostratus.
  • Dogs are infested by chewing and biting lice.
  • Lice are highly species specific and complete the life cycle on the host.
  • They survive for only a few days off the host.
  • Clinical signs can vary from none to variable degrees of pruritus, self-inflicted alopecia, scaling and inflammation.
  • Louse infestation is generally easy to treat.
  • Treat the environment and all in-contact animals of the same species.

References

Defalque VE. Isoxazolines for treating canine demodicosis, sarcoptic mange (scabies), and lice infestation. Can Vet J 2022; 63: 1159-1162.

Azaria H, Defalque VE. Isoxazolines for treating canine and feline otodectic mange; feline demodicosis, lynxacariasis, lice infestation, and notoedric mange (scabies); demodicosis in hamsters; and sarcoptic and psoroptic manges in rabbits. Can Vet J 2023; 64: 1066-1070.

Miller WH, Griffin CE, Campbell KL.  Small Animal Dermatology, 7th edn. St. Louis, MO: Elsevier, 2013; 320-322.

Mihalca AD, Deak G, Panait LC, et al. Efficacy of afoxolaner (NexGard®) against natural infestations with Trichodectes canis in dogs under field conditions.  Parasit Vectors 2022; 15: 317.

Mihalca AD, Deak G, Panait LC, et al. Efficacy of a topical formulation containing esafoxolaner, eprinomectin and praziquantel (NexGard Combo) against natural infestations with the cat louse, Felicola subrostratus under field conditions. Parasite 2022; 29: 62.

Scott DW, Miller WH, Griffin CE.  Small Animal Dermatology. 5th edn. Philadelphia: W.B. Saunders Co., 1995; 445-448.

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Small and Large Animal Dermatology Handbook, Vol. 1 Copyright © 2025 by Sheila M.F. Torres, DVM, MS, PhD, DACVD is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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