A male patient reports painful vesicular eruptions on the penis. Based on this presentation, which of the following is the most likely causative agent?

1. A

   A. Haemophilus ducreyi

2. B

   B. Human papillomavirus

3. C

   C. Herpes simplex virus

4. D

   D. Treponema pallidum

Appeared in: INI-CET EXAM -2026

Explanation

• Herpes simplex virus (HSV), typically HSV-2, is the primary cause of genital herpes.
• The characteristic initial lesion of genital herpes is a cluster of small, painful vesicles (blisters) on an erythematous (red) base, as described in the question and shown in the image.
• These vesicles eventually rupture, leaving shallow, painful ulcers that then crust over and heal.
• The presence of both pain and vesicles strongly points to HSV as the causative agent.

Why Other Options Were Wrong

• Option A: Haemophilus ducreyi causes chancroid. The characteristic lesion is a painful, soft ulcer with ragged edges, not a vesicle.
• Option B: Human papillomavirus (HPV) causes genital warts (condylomata acuminata). These lesions are typically painless, solid, fleshy, cauliflower-like growths, not fluid-filled vesicles.
• Option D: Treponema pallidum causes syphilis. The primary lesion (chancre) is classically a single, firm, indurated, and painless ulcer with a clean base, not multiple painful vesicles.

Related Visual

Clinical Relevance

• Nursing practice connection: Prioritize focused assessment, early escalation, and real-time monitoring when managing Identification of causative agents for sexually transmitted infections based on clinical presentation of genital lesions in acute care settings.
• Accurate identification of genital lesions is crucial for correct diagnosis, treatment, and patient education. Misdiagnosis can lead to ineffective treatment and continued transmission.
• Nurses play a key role in educating patients with genital herpes about its chronic nature, the possibility of recurrent outbreaks, and the risk of asymptomatic viral shedding, which can transmit the virus to partners even when no lesions are present.
• Patient counseling should include information on suppressive antiviral therapy, safe sex practices (condom use), and the importance of informing sexual partners.

How to Approach the Question

• First, analyze the keywords in the question stem. The key descriptors are 'painful' and 'vesicular eruptions'.
• Next, examine the provided image to visually confirm the description. The image clearly shows small blisters (vesicles).
• Systematically evaluate each option based on your knowledge of sexually transmitted infections.
• Recall or deduce the classic lesion for each pathogen: HSV (painful vesicles), H. ducreyi (painful ulcer), HPV (painless warts), T. pallidum (painless ulcer).
• Match the patient's presentation (painful vesicles) to the correct pathogen. Only Herpes simplex virus fits this description.
• Eliminate the other options because their lesion characteristics (ulcer, wart) and pain profile do not match the case.

Concept Tested & Keywords

• Concept Tested: Identification of causative agents for sexually transmitted infections based on clinical presentation of genital lesions.
• Stem keywords: painful vesicular eruptions, penis, causative agent
• Lead-in keywords: most likely
• Clinical cues: The combination of 'painful' and 'vesicular' are the key diagnostic clues in the stem.
• Clinical cues: The image showing a cluster of blisters is a classic presentation of genital herpes.

Question ID

QoqzZZUq1ULiTOxkNiiCdr

Copy ID

Reference Book

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 pp. 1255-1257, 1763-1765