Louse Infestations

Pediculosis can be caused by sucking lice (Anoploura, such as Linognathus setosus in dogs) or chewing lice (Mallophaga, such as Felicola subrostrata in cats and Trichodectes canis or, in warm climates, Heterodoxus spiniger in dogs).

Nits (louse egg cases) are usually visible, adherent to the hair. The hair coat is often matted and dirty. Lice infestation is associated with neglect (overcrowding, poor sanitation), and affected animals are often debilitated. Anemia can be associ­ated with heavy Linognathus setosus infestation because sucking lice feed on blood. Asymptomatic carriers exhibit only mild pruritus and seborrhea sicca.

Differential diagnosis includes flea-allergy dermatitis, scabies, cheyletiellosis, Dermanyssus or Trombicula infestation, Malassezia dermatitis, allergic skin diseases, and seborrheic disorders. Acetate tape allows lice immobilization and identification by microscopic observation. Hair coat observation with the video otoscope is another possibility. Nits are visible both on macroscopic and microscopic examination. They are larger and more tightly attached to the hair than Cheyletiella eggs.

In dogs and cats, most routine insecticides are active on adult lice (spray, sham­poo, powder, dips), which might explain the observed decrease in pediculosis preva­lence. Nevertheless, treatments are usually ineffective on eggs and have to be applied repeatedly.