A one year study on the viability of Cryptococcus neoformans in nature

Abstract

Using four different assay procedures we found a 50 to 86% decrease in viability of Cryptococcus neoformans over a one year period after two towers in the Oklahoma City area were modified to exclude pigeons and weather elements, especially rain. In homogeneous pigeon dropping samples a sharp decrease in viability occurred after 7 to 9 months of storage. The decrease occurred in pigeon dropping samples maintained at the natural sites and at ambient temperature in the laboratory but not in droppings stored at −4 °C. Air sampling studies done at the natural sites before and after tower modifications also showed a decrease in C. neoformans viability. The decrease in viability cannot be explained by seasonal temperature variations that occurred at the natural sites. Our findings suggest that death of C. neoformans occurred because of lack of available intracellular water exacerbated by low humidity, exclusion of precipitation and moisture from fresh pigeon droppings.

In light of our experiences, at one site in south central United States, the feasibility of controlling C. neoformans at heavily contaminated sites, other than by the use of noxious or potentially dangerous chemicals, is discussed.