TABLE OF CONTENTS
Pediculosis (Lice Infestation) in Animals
Pediculosis is a common ectoparasitic condition caused by lice infestation in animals. Lice may cause pruritus, skin irritation, alopecia, reduced productivity, and, in severe cases, anemia. The severity of infestation depends on factors such as louse density, host species, age, health status, and environmental conditions. This article covers the effects of pediculosis, common lice affecting domestic animals, and general treatment and control measures.
In medical and veterinary entomology, lice are well known as vectors of diseases such as typhus and louse-borne relapsing fever.
Clinical Signs and Effects of Pediculosis
The effects of lice infestation are usually a function of their density. A small number of lice may present no problem and may, in fact, be a normal part of the skin fauna. Heavy louse infestations may cause pruritus, alopecia, excoriation, and self-wounding. The resulting disturbance may cause lethargy and reduced weight gain or egg production.
Severe infestations with sucking lice may cause anemia. Heavy infestations are usually associated with young animals or older animals in poor health.
Factors Affecting Louse Infestation
Louse infestations are more common in cattle than in other domestic animals. In temperate seasonal habitats, the heaviest louse infestations occur in late winter and early spring, when the coat is thickest, providing a protective, humid environment. This may be exacerbated by winter housing, particularly if the animals are in poor condition or are deprived of the opportunity to groom themselves properly while housed in stanchions.
Most of the louse population may be lost when the winter coat is shed. Louse infestation may also be indicative of another underlying problem, such as malnutrition or chronic disease.
Clinical Signs
Hosts become restless, may not feed or sleep well, and may injure themselves by biting and scratching the parts of their bodies irritated by lice. They may also overgroom or damage their feathers, hair, or wool. The skin of people who harbor large numbers of lice may become thickened and pigmented, and the condition is known as vagabond’s disease.
Egg production in birds and milk production in cattle may decrease. In mammalian hosts, scratching may produce wounds or bruises, while in sheep, the wool may be damaged. It may also become soiled by louse feces. The coat becomes rough and shaggy, and if the irritation is severe, the hair may become matted.
Heavy lice infestations cause irritation in animals. Due to continuous irritation, an animal may bite the affected area, pull out the hair, and swallow it, which may lead to the formation of hairballs in the stomach.
Common Lice in Animals
The foot louse of sheep (Linognathus pedalis) is found most frequently around the dewclaws, and severe infestations may produce lameness.
Some species of dog lice (Heterodoxus spiniger and Trichodectes canis) may act as intermediate hosts for the dog tapeworm, Dipylidium caninum, and the pig louse, Haematopinus suis, may transmit swinepox virus and Mycoplasma suis.
Treatment & Control
- Topical ectoparasiticides: Pyrethroids, macrocyclic lactones (selamectin), etc.
- Systemic treatment: Macrocyclic lactones such as ivermectin may be effective against susceptible sucking lice in some species.
- Repeat treatment: Because many insecticides have limited activity against louse eggs (nits), treatment may need to be repeated according to the louse life cycle.
- Treat in-contact animals: Animals that have close contact with the affected animal should be examined and treated to reduce the risk of reinfestation.
- Environmental management: Bedding, grooming equipment, housing areas, and other items that may harbor lice should be cleaned or treated appropriately, particularly in cases of heavy infestation or group housing.
