The human papillomavirus (HPV) causes mosaic warts. The virus infects cells in the skin known as keratinocytes. As a result, the skin gets thicker and tougher, creating a wart or warts.
A person can get HPV through direct contact with a person who has it or by touching contaminated surfaces. Examples include bare feet touching a contaminated shower floor or swimming pool. The virus enters through small breaks in the skin. Moisture makes the virus easier to enter.
Read more at: https://www.healthline.com/health/mosaic-warts