Facial eczema, FE, is a disease that mainly affects ruminants such as cattle, sheep, deer, goats, and South American camelids (alpaca, llamas). It is caused by the fungus Pithomyces chartarum that under favorable conditions can rapidly disseminate in pastures. The fungus requires warm, humid weather with night-time temperatures over 13°C (55°F) for several days, and litter at the bottom of the sward.
P. chartarum occurs worldwide, but is a problem predominantly where farm animals are intensively grazed, especially in New Zealand. The spores of the fungus release the mycotoxin sporidesmin in the gastrointestinal tract, causing a blockage in the bile ducts that leads to injury of the liver. Bile, chlorophyll, and other waste products consequently build up in the bloodstream, causing photosensitivity of the skin, especially that exposed to direct sunlight. This, in turn, causes severe skin irritation that the animal attempts to relieve by rubbing its head against available objects, resulting in peeling of the skin.
The large family of fungi that produce mycotoxins, of which sporidesmin is one, live mainly on ryegrasses and can cause significant problems in grazing animals. Sporidesmin can lower an animal's immunity and affect total production in farm animals, and when taken in larger quantities, can result in death.
The clinical symptoms of FE are distressing: restlessness, frequent urination, shaking, persistent rubbing of the head against objects (e.g. fences, trees etc.), drooping and reddened ears, swollen eyes, and avoidance of sunlight by seeking shade. Exposed areas of skin develop weeping dermatitis and scabs that can become infected and attractive to a blow-fly, causing myiasis.