Sheep louse

The sheep louse (Linognathus ovillus) is a member of the order Phthiraptera and the family Linognathidae. It is a blood-sucking louse that spends its entire life cycle on the sheep.

The adult louse is small, measuring approximately 2 mm in length, with a head shaped to facilitate blood-feeding. They are wingless and move between fibers using specialized claws.

The life cycle consists of eggs (nits), three nymphal instars, and adults. These stages occur entirely within the fleece of the animal.

Eggs are firmly cemented to the hair shafts near the skin surface, making them resistant to removal by weather or environmental conditions.

The species is highly host-specific, adapted to the specific skin temperature and hair density of domestic sheep.

Linognathus ovillus causes linognathosis, a parasitic condition affecting the health and welfare of sheep flocks globally.

By feeding on blood, these parasites cause irritation and anemia, particularly in lambs or heavily infested animals during winter.

The constant irritation causes sheep to scratch, bite, and rub against structures, leading to significant wool loss and physical damage to the fleece.

The resulting skin lesions may become sites for secondary bacterial infections, further weakening the animal and reducing its productivity.

Poor skin condition and constant stress translate into lower weight gains and decreased overall fitness of the affected flock.

Restlessness in the flock is the most common early sign of an infestation, as animals spend more time rubbing against fences or feeders.

Close inspection of the wool, especially around the face, neck, and shoulders, will reveal clusters of lice and eggs attached to the hair.

Damaged, matted, or thinning wool patches are clear indicators that a heavy infestation may be present in the affected area.

The skin surface often shows redness, scabs, and scratch marks as a direct consequence of the persistent itching caused by the parasites.

In cases of severe infestation, anemia manifests as pale gums and conjunctiva, signaling that blood loss is impacting the health of the sheep.

Effective management requires a combination of chemical treatment and good husbandry practices to keep parasite numbers low.

• Strategic dipping or spraying with insecticides immediately after shearing when the wool is short.
• Use of pour-on or injectable macrocyclic lactones for systemic control of lice.
• Routine quarantine of incoming sheep to prevent introducing lice into a clean flock.
• Proper cleaning and disinfection of housing facilities to reduce the risk of re-infestation from the environment.

Total eradication is difficult, so management programs should focus on reducing infestation levels below the threshold of economic and physical damage.