Besnoitiosis is a protozoal skin disease of donkeys (and more rarely horses) caused by the organism Besnoitia bennetti. It causes multiple tiny cystic skin lesions, mostly around the muzzle and face.

This disease is endemic and more commonly occurs in tropical and semi-tropical regions. How the disease is transmitted and where it comes from is currently unknown. It is a more important disease of cattle, and similar disease occurs in many other species.

The disease is characterized in equines by the appearance of many pinpoint cystic lesions that appear on the face, ears, nostrils and body. Tiny pale cysts on the surface of the eye, called "sclera pearls" are a classic characteristic of this disease. Often, Besnoitiosis does not cause any other illness and signs may be mild. However, in some cases infected animals may develop a poor hair coat, crusty skin lesions, sustain patchy areas of hair loss, or become weak and lose weight. Only rarely does this disease cause death.

In 2005 this disease surfaced in the United States in a group of donkeys, leading to speculation that the disease is more common in donkeys than once thought. There is speculation that it may be an emerging disease in the United States.

Diagnosis is currently mostly by skin biopsy, although blood testing may have some value. Donkeys with the disease may have signs within the upper airway on endoscopy.

There is currently no effective treatment for the disease. Antiprotozoal drugs have not been effective.