A fungus of the toenail can take hold on your feet when nails are pushed away from the nail bed or otherwise injured. Try to find shoes that are wide enough for your feet, and will accomodate comfortable walking all day. Many better shoe companies make their designs in varying widths. The wart virus is picked up by the body from somewhere in the everyday environment. People are exposed to wart virii all the time.
Some people grow warts, and some fight off the virus.
What causes people to contract and grow warts is believed to be a defect in the immune system. The body simply doesn't fight the virus off as it normally would. The virus causes an overgrowth of skin in the infected area. This growth also strangulates blood vessels in the infected area. These strangulated blood vessels are the black dots commonly seen at the surface of a wart.