giddy

Gid is a parasitic disease of ruminants, particularly sheep, caused by the larval stage of the tapeworm Taenia multiceps. When infected, the animal becomes giddy: it walks in tight circles, stumbles, loses coordination, and may appear disoriented or distressed. The condition results from coenuri (fluid-filled cysts containing tapeworm larvae) forming in the brain tissue, creating pressure that disrupts normal neurological function.

The disease cycle begins when sheep graze on pasture contaminated with tapeworm eggs shed by infected dogs or other canine hosts. The eggs hatch into larvae that migrate through the sheep's body and lodge in the central nervous system. Development of the cysts takes weeks to months, so an affected animal may show no symptoms during the early infection period, then suddenly develop acute neurological signs.

Recognition and practical impact

A giddy sheep is obvious: it performs involuntary circular movements, often in one direction repeatedly, and may fall or injure itself against obstacles. The spinning is not deliberate behavior but a compulsive response to the physical pressure on the brain. Affected animals become unthrifty, lose condition, and cannot be retained in a commercial flock. Treatment is unreliable once cysts are established; most infected sheep are culled to prevent spread to other animals and to reduce the reservoir of infection in the flock.

The term remains dialectal in British and Irish agricultural speech, though the disease itself is recognized globally. Prevention focuses on controlling the definitive host (dogs) through deworming and preventing access to infected carrion or offal, combined with rotational grazing to reduce pasture contamination. The disease is now less common in intensive sheep systems but persists in pastoral and mixed farming regions where dog control is less rigorous.