Ugh, I got plantar warts in high school, along with my brother. We all went barefoot everywhere, but when asked the doctor said the most likely source was from the public showers in the school and not from any barefoot outdoor activities. His were caught quickly because he could feel them, but I've never felt certain types of pain easily so mine were HUGE by the time I notice there were weird spots on my feet. I didn't mind having chunks of my foot cut out by the podiatrist, but I sure resented having to wear shoes while they healed. As a result of that little experience I tumble around all over the place without shoes, but I will not set foot in a public shower without my grungy tennies. Animals are one thing, but when it comes to good odds of catching terrible and disgusting stuff . . . well, in that case you need to avoid humans.