Sporobolomyces: a possible cause of extrinsic allergic alveolitis

A 28-year-old horseback rider presented with symptoms, chest radiograph, and pulmonary function tests suggestive of extrinsic allergic alveolitis related to exposure to a horse barn. Exposure to the barn produced symptoms, fever, and a fall in VC commencing 4 hr after exposure. Precipitins were positive against Sporobolomyces, suggesting this might be the causative agent; precipitins were negative against other fungi and horses. Lymphocyte stimulation to Sporobolomyces in vitro was positive in the patient and negative in two control subjects. Sporobolomyces was grown from straw in the barn. Cessation of exposure to this barn (but continued exposure to horses) has resulted in improvement in clinical condition. A survey for immunologic sensitivity to Sporobolomyces revealed that eight of 30 atopic subjects had positive wheal-and-flare prick skin tests to Sporobolomyces antigen, whereas none of 30 laboratory controls or 30 grain handlers had precipitins against Sporobolomyces. Sporobolomyces is a common fungus in cereal grain growing areas. Its spore size is less than 5 micron, consistent with other causative agents of this disorder. In this patient, positive precipitins and lymphocyte stimulation to Sporobolomyces and negative precipitins to other known causes of extrinsic allergic alveolitis provide circumstantial evidence that Sporobolomyces was the cause of the syndrome.