Isolation of Histoplasma capsulatum from Soil in Washington, D.C.

Abstract

IN THE FALL of 1960, Histoplasma capsulatum was isolated from 10 of 10 specimens of soil collected in a small park in downtown Washington, D.C. In order to clarify and emphasize the significance of the demonstration that this pa.thogenic fungus grows freely in urban as well as rural habitats on the Atlantic seaboard, it is necessary to review some of the history of Histopltsma and histoplasmosis. H. capsulatfum was isolated from a saprophytic source for the first time in 1948 (1). Both the local site and the geographic area from which the first positive soil specimen came are historically and scientifically significant. This, specimen was collected near the entrance to a rat burrow under the edge of a chickenhouse in Loudoun County, Va. Later isolations of H. capsulatum from soil taken from many farm premises in both northern Virginia and eastern Maryland (2), the report of four fatal human cases of histoplasmosis in northern Virginia in 1946 (3), the discovery that in this area seven species of animals are natural hosts of H. capsulatum (4), and the observation that as many as 83 percent of persons in one intensively studied community a-re hypersensitive to histoplasmin (5) conclusively demonstrate that H. capsulatumn is a frequent contaminant of man's environment and that histoplasmosis is a common disease and an important medical problem on the Atlantic seaboard. Some workers, in discus-sing the epidemiology of histoplasmosis, have persistently ignored these facts. Epidemiologic studies of many cases of histoplasmosis in residents of the District of Columbia have included searches for H. capsulatum in the urban environments of the patients (2). Up to the time of this study no isolations of this fungus had been reported from soil collected within the District of Columbia. We had isolated the fungus many times from soil (usually around chickenhouses) to which District of Columbia resident patients had been exposed during visits or temporary residence in nearby Maryland or Virginia. Because of persistent confused or erroneous concepts expressed in the literature of the mycoses, the epidemiology of histoplasmosis cannot be discussed without reference to the epidemiology of cryptococcosis. The prese,nt study, although it re.sulted in isolations of Histoplasma, was directed toward a search for Cryptococcus neofor?nrwns. The first reported isolation of C. neoformans since 1896 from a source unrelated to human or animal infection was also from the Washington, D.C., area (6). This report was followed by the demonstration that C. neoformmans is a, frequent inhabitant of accumulations of pigeon droppings in old nests or beneath roosting sites under conditions in which this material has not become composted with soil (7). This purely saprophytic association between virulent strains of C. neofor?mans and pigeon droppings has been confirmed in several parts of the world and in Washington, D.C., by repeated examinations of such material collected from the attics of old school houses, cupolas on school houses and other public buildings, the ledges outside windows of office buildings, and many similar locations (8). Both H. capsulatum and C. neoDr. Emmons is head of the Medical Mycology Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, Public Health Service. (Paper received Feb. 6, 1961.)