Photosensitization associated with exposure to Pithomyces chartarum in lambs

An epidemic of photosensitization was observed in a group of lambs on irrigated autumn pasture in western Oregon. Signs included crusting, necrosis, and sloughing of the skin over the nostrils, lips, and ears, and of the mucous membranes of the buccal regions. Microscopic examination of plant material from the pasture disclosed spores of Pithomyces chartarum. This fungus has been documented as a causal factor in photosensitization in sheep and cattle (facial eczema) in other parts of the world. An infective agent or other plant material that could have induced the clinical signs in the lambs was not evident. Weather and humidity conditions were ideal for fungal growth during the grazing period, and the fungus was detected in large numbers before and during the epidemic. Even though facial eczema has not been reported previously in northwestern United States, we feel the circumstances surrounding this epidemic warrant such a diagnosis.