A 10 year old boy develops an itchy, vesicular rash, which is maximal on his face and trunk. Physical examination demonstrates a mixture of lesions, with macules, papules, vesicles, and crusted lesions. The mother repos that the lesions seem to be occurring in crops. Which of the following is the most likely diagnosis?

This is varicella (chicken pox), which is the primary form of infection by the herpes zoster (varicella-zoster) virus. Recurrence due to virus harbored in neurons tends to be dermatomal in distribution and is called shingles. Fever, malaise, headache, and myalgia may also be present, paicularly in the prodromal phase. Tzanck smear of the base of a vesicle may demonstrate multinucleated giant cells. Immunocompromised patients can be treated with acyclovir to prevent dissemination. Chicken pox may be complicated by secondary bacterial infection, pneumonia, systemic spread (immunosuppressed patients), neurologic involvement (rare), Reye's syndrome (rare), and hemolytic anemia (rare). Herpes simplex I causes oral vesicles and ulcers. Herpes simplex II causes genital vesicles and ulcers. Measles causes a blotchy, non vesicular rash. Ref: Ray C.G., Ryan K.J. (2010). Chapter 14. Herpesviruses. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.