Soil and Human Pathogens.

Soils of the world harbor a myriad of organisms that are involved in many important nutrient cycles and soil functions. Soils also may harbor pathogenic organisms that can negatively impact humans who live upon soil and are exposed to soil by direct contact, ingestion, or inhalation. This review will discuss the ‘bad guys’ in the soil, how they survive and how they are transmitted. Some pathogens are soil residents spending their life cycles in soil. They take part in normal soil ecosystem services but, under certain conditions, may become human pathogens. Included in this group are lethal bacteria causing anthrax, tetanus, and botulism. Other pathogens are intestinal enterics originating in animal or human guts. These are transitory soil organisms that may not reproduce but can survive in soil until contacting a new host. Survival is affected by sunlight, moisture, temperature, pH, organic matter, texture, and predatory fauna. These organisms most often originate in animal and human feces. Pathogens may move in the soil or may move into surface or groundwaters. Movement is often related to size of the organism and whether saturated, unsaturated, or preferential water flow is involved. Helminths are approximately the size of the sand particles, protozoa the size of silt particles, bacteria the size of coarse clays, and viruses the size of fine clays. Soil pH (and organismal isoelectric point), cation exchange capacity, cation composition and strength, and organic matter influence movement. The involvement of uncultured soil organisms, currently thought to be in the thousands of different species per gram of soil, and human health is little understood. Perhaps early exposure of infants to the soil microflora affects the infant’s intestinal microbiota and immune systems. Much yet remains to be discovered about these uncultured organisms.