Trees, Birds & Health

The townspeople of little Milan, Mich, watched with satisfaction last week as a work crew cut down the fine old elms and maples around the junior high school parking lot. It was not that they did not love trees. But an odd combination of trees plus bird droppings plus fungus spores plus children had given Milan (rhymes with pylon) a strange epidemic.

During a tuberculosis survey of Milan in 1958, schoolchildren had been given scratches on both arms: one for the tuberculin test, the other for histoplasmosis. This disease, which is like TB in the variety of its effects--ranging from an undetectable, mild infection to fulminating and rapidly fatal cases--is caused by a fungus, Histoplasma capsulatum. Unrecognized until 50 years ago, histoplasmosis is still often mistaken for, and mistakenly treated as, TB. It is now known to be especially common in the mid-continent states. But Milan's infection rate turned out to be an astonishing 62%, contrasted with 8% in adjoining towns.

It took Dr. Horace Dodge, University of Michigan epidemiologist, more than two years to figure out the reason. Most of the children, he found, got infected soon after they began to attend classes in the junior high school building, where the school bus parking lot and the playground were shaded by the trees. In the bare soil beneath the trees. Dr. Dodge found His to plasma fungi galore. Kids scuffing through the lot kicked up dust containing the fungus' spores, which, when inhaled, caused the infections. The dust and spores were also sucked in by the air intake of the school's ventilating system.

This ground was more than usually fertile for Histoplasma, Dr. Dodge found, because in the late summer and early fall, starlings used the treetops as a dormitory. Their droppings, which covered the ground, have the right chemical composition and acidity for Histoplasma to flourish. In cities starlings usually roost in buildings, but even where they stay in trees the terrain underneath is generally lawn or pavement; Milan just happened to offer the right circumstances. To make Milan's school parking lot and playground inhospitable to Histoplasma, the town will blacktop them as soon as the frost is out of the ground.

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