There is a significant risk of infection from walking barefoot.
In
Parasites: Tales of Humanity's Most Unwelcome Guests, Rosemary Drisdelle writes about the
hookworm, a parasite that is spread through feces. The eggs in an infected mammal's feces enter the soil, and then the infective larvae of the hookworm enter the body of a new host through the skin The parasite penetrates skin, typically
through the feet of people who walk barefoot, and moves to intestine.
The hookworm was introduced to the United States by slaves from Africa.
While the slaves were relatively immune to it, whites of American South walked barefoot and contracted the parasite.
Hookworm causes severe anemia. It caused weakness of many soldiers in the Confederate Army, thereby contributing to the defeat of the Confederacy and the freedom of the slaves who brought it.