Lice are small, wingless, dorsoventrally flattened insects of the order Phthiraptera that live their entire life cycle on the body surface of a host animal, feeding on skin debris, secretions, or blood depending on species. In horses, infestation with lice (pediculosis) is most common during winter and early spring when horses are kept in close contact, have longer coats, and reduced grooming. Heavy infestations cause intense pruritus (itching), hair loss, skin irritation, and restlessness, and can lead to weight loss in severe cases due to the metabolic cost of chronic stress and reduced feed intake.
Two species primarily infest horses: Damalinia equi (also called Werneckiella equi), a biting or chewing louse that feeds on skin scales and debris, and Haematopinus asini, a sucking louse that pierces the skin to feed on blood. The biting louse is more common and is found in the mane, forelock, tail base, and along the topline; the sucking louse favors the head, neck, and inner legs where skin is thinner. Both species attach their eggs (nits) firmly to individual hair shafts, distinguishing an active infestation from simple debris or dandruff. The mane and forelock should be checked during routine grooming by parting the hair and inspecting the skin surface.
Lice are host-specific and do not infest humans, so the zoonotic risk is negligible, but lice spread readily between horses through direct contact or shared grooming equipment, blankets, and tack. Diagnosis is by direct visualization; lice and nits are visible to the naked eye on close inspection. Treatment involves topical insecticides (pyrethrin, permethrin, or organophosphate-based products), applied twice fourteen days apart to catch eggs that were not killed by the first treatment. All horses in contact should be treated simultaneously. New horse owners should include a lice check in their quarantine protocol alongside a fecal parasite baseline and vaccination review.
Further Reading
- louse (Wikipedia)
- For diagnosis, treatment, and prevention of equine pediculosis: lice of horses — Merck Veterinary Manual