A 6-month-old infant presents to the pediatrician's office with a two-day history of increased fussiness, poor feeding, low-grade fever and rash. The family returned from a trip to India last week. The rash appears on the trunk in several stages of erythematous macules, vesicular papules and pustules. Which of the following is the most likely diagnosis?

A. Herpes simplex

B. Measles

C. Pityriasis rosea

D. Varicella

The correct answer is D. The most likely diagnosis is varicella.

Explanation:

Varicella is a highly contagious disease caused by human herpes virus 3 (HHV-3), that affects mostly children and is a fairly common child disease. The disease can be prevented by vaccination, but as the disease usually proceeds relatively peacefully and leaves the person with lifelong immunity to the disease, most countries omit the disease in their vaccination program. The incubation time is 1 - 3 weeks. The disease transmits by direct contact, but it is also airborne.

The disease starts with mild fever, cough and possibly headache. After two to five days, a red characteristic rash appears. Some people are not so badly attacked and only get a minor rash, while others get red dots over most of the body. After a few hours, the red dots develop into liquid blisters, which after a few days burst and form a crust. Often the red rash occurs in one - three waves during the course of the disease. Until all blisters have formed a crust, the person can infect other people. Scratched holes on the blisters can leave scars on infection.