A 10-year-old boy comes to your clinic with his father for evaluation of a rash that started on his wrists and ankles, then later spread to his palms, soles, and trunk, present for 4 days. His father stated that they returned home from a hill station two weeks ago and following that his son had developed a headache and mild fever. The physical examination reveals a rash on his hands, feet, and trunk as shown below. What is the probable diagnosis?