Ulcus Molle — Chancroid

Acute sexually transmitted bacterial infection caused by Haemophilus ducreyi.

Aetiology

Causative organism:
  • Haemophilus ducreyi
Microbiological characteristics:
  • Gram-negative coccobacillus
  • Non-motile, non-spore forming
  • Facultative anaerobe
  • Requires enriched media (chocolate agar with hemin)
  • Arranged in characteristic “school of fish” or “railroad track” pattern on Gram stain

Pathophysiology

  1. Entry through minor skin or mucosal trauma
  1. Local bacterial multiplication
  1. Tissue necrosis and ulcer formation
  1. Intense inflammatory response
  1. Regional lymphatic spread → bubo formation
Key venereology principle:
No protective immunity → reinfection possible.

Clinical presentation

Incubation Period

  • 3–7 days (short)

Primary Lesion

  • Begins as:
    • Erythematous papule → pustule → ulcer
Ulcer characteristics (classic):
  • Painful
  • Soft (non-indurated) base
  • Ragged, undermined edges
  • Friable, necrotic base with purulent discharge
  • Bleeds easily on touch
Number:
  • Often multiple (autoinoculation common)
notion image

Regional Lymphadenitis (Bubo)

  • Develops in ~50% of patients
  • Usually unilateral
  • Painful, tender inguinal nodes
  • May suppurate and rupture through skin
notion image

Investigations

  • Gram stain
    • Gram-negative coccobacilli
    • “School of fish” pattern
    • Low sensitivity
  • Culture
    • Special media
    • Technically difficult
    • Limited availability
  • PCR (NAAT)
    • Most sensitive and specific
    • Not widely available in many settings

Management

  • Ciprofloxacin 500mg BID PO for 3 days
  • Azithromycin 1G SD PO
  • Erytrhomycin 500mg QID PO for 7 days
  • Ceftriaxone 250mg SD IM