The most appropriate test to confirm herpes infection in a vesicular genital lesion is which?

• A. Culture of a vesicle using blood agar medium
• B. The presence of similar lesions on the fingers and hands
• C. A Gram stain of a scraping from the base of the lesion
• D. The presence of giant multinucleated cells on Tzanck smear

Answer: (D)

Herpes infection causes a distinctive cytopathic effect in infected squamous cells, which can be seen quickly with a Tzanck smear. In this test, scraping the base of the vesicle is examined for giant multinucleated cells, a hallmark of herpesvirus activity. This finding provides rapid supportive evidence that the vesicular genital lesion is due to a herpes infection.

The other options don’t fit as well. Culturing a vesicle on blood agar targets bacteria and won’t recover herpes virus. The presence of similar lesions on the fingers is a clinical clue, not a diagnostic test. A Gram stain from the lesion base looks for bacteria, not viral cytopathic changes. So the Tzanck smear’s appearance of giant multinucleated cells best aligns with herpes infection among the choices.

Note: while a Tzanck smear supports herpes infection, it cannot distinguish HSV from VZV; for a definitive HSV-specific diagnosis, PCR or viral culture is preferred.