Time required for the production of hay fever by spores of a newly encountered fungus, johnson grass smut

Abstract Johnson grass smut, variously classified as Sphacelotheca sorghi, S. cruenta, or S. holci, was first observed in Arizona in 1931, and by the writer in 1933. Its distribution and prevalence have increased each year. Spores of this smut are found by gravity on slides during eight or more months of each year, and they are at times by far the most numerous particulate objects so found. Extracts of this smut, used intradermally in testing hay fever patients resident in Arizona, elicited no positive reactions in 1935, and none in subsequent years until the fall of 1938. In 1939, 131 persons known to be sensitive to inhaled allergens were tested with smut. Thirty-four had clear and typical positive reactions; one had a mild shock from the intradermal test. All the positive reactors had lived for at least five years in regions where the smut was prevalent. Fifteen of the positive reactors experienced recurrences of hay fever or asthma and were promptly relieved when smut extract was added to their otherwise adequate treatment. So far, the smut has been a subsidiary, rather than a primary, cause of inhalant allergy. In this series of cases, at least five seasons of exposure to the spores of Johnson grass smut were required to induce cutaneous and clinical sensitivity to that fungus.