Ovine and Caprine External Parasites – NAVLE Study Guide

Overview and Clinical Importance

External parasites (ectoparasites) of sheep and goats represent a significant challenge in small ruminant practice and are commonly tested on the NAVLE. These parasites cause direct economic losses through reduced weight gain, decreased milk and wool production, hide damage, and transmission of infectious diseases. Major categories include lice (pediculosis), mites (mange), sheep keds, ticks, and blowfly strike (myiasis). Understanding the life cycles, clinical presentations, and treatment protocols is essential for board examination success.

1. Lice (Pediculosis)

Pediculosis is infestation with lice, wingless, dorsoventrally flattened insects that spend their entire life cycle on the host. Lice are highly host-specific and transmission occurs primarily through direct contact. Infestations peak during winter months when animals are housed closely together.

Types of Lice

Biting (Chewing) Lice - Mallophaga

Biting lice have broad, rounded heads with chewing mouthparts. They feed on skin debris, epidermal tissue, hair, and exudates. Important species include: Bovicola (Damalinia) ovis (sheep body louse), Bovicola caprae (goat biting louse), and Bovicola crassipes (Angora goat louse).