What is the most likely diagnosis for this 19-month-old girl who presented with a 1-week history of an ascending erythematous eruption?

Answer C. Herpes zosterThe results of a scraping from the base of several vesicles were positive for the varicella-zoster virus. The lesions resolved within 2 weeks of treatment with acyclovir. Herpes zoster is unusual in persons younger than 10 years of age, and when it does occur in this age group, the lesions have a predilection for dermatomes supplied by the cervical and sacral nerves.