History and Epidemiology
Haemophilus ducreyi was first isolated by O.V. Petersen in 1887 and described in detail by A. Ducrey in 1890, after whom the species is named.
Chancroid is a classic sexually transmitted infection. Humans are the only reservoir. Transmission occurs almost exclusively via sexual contact, though rare non-sexual contact transmission is possible. Epidemiological hotspots are most frequently reported in developing regions of Africa and South America.
Clinical Presentation and Pathogenesis
The incubation period for Haemophilus ducreyi is relatively short: averaging 3 to 5 days, though initial clinical lesions can appear within 24 hours of exposure.
Pathologic changes primarily involve the genitalia. However, due to autoinoculation (transferring the organism via hands to other body sites), extragenital lesions can occur.
Key morphological features of chancroid:
- Formation of a painful, soft ulcer with ragged, undermined edges.
- Marked surrounding soft-tissue edema.
- Regional lymphadenopathy—lymph nodes become significantly enlarged and exquisitely tender (buboes).
The infection typically shows slow ulcer healing. Without intervention, there is a risk of systemic dissemination.
Differential Diagnosis
A critical step is differentiating chancroid from the hard chancre of primary syphilis.
| Feature | Chancroid (H. ducreyi) | Hard Chancre (Syphilis) |
|---|---|---|
| Pain | Exquisitely painful on palpation | Painless |
| Bleeding | Easily bleeds | Bleeding not typical |
| Base/Consistency | Soft, non-indurated base | Firm, indurated (cartilaginous) base |
Laboratory Diagnosis
Diagnosis relies on clinical presentation and laboratory confirmation using swabs from the base or margins of the ulcer.
- Microscopy. Gram staining reveals small Gram-negative rods. Note that Haemophilus ducreyi often appears alongside heavy mixed pyogenic flora.
- Culture. Isolating the organism requires specialized media. The bacterium requires X-factor (hemin), but does not require V-factor (NAD). Culture is performed on chocolate agar supplemented with vancomycin to inhibit contaminating flora. Incubation occurs at 33 °C in a humid, CO₂-enriched atmosphere. Characteristic small, greyish colonies grow without hemolysis.
- Molecular Testing. Multiplex PCR assays are increasingly used for rapid and highly sensitive detection of H. ducreyi DNA in clinical specimens.
Treatment and Prevention
Since specific vaccination is unavailable and prior infection confers no lasting immunity, management relies on prompt antibiotic therapy.
First-line regimens include:
- Azithromycin;
- Ceftriaxone;
- Ciprofloxacin;
- Erythromycin.
Antimicrobial Resistance: Strains historically resistant to older regimens (such as tetracyclines, sulfonamides, and penicillin) are common, making them unreliable choices in modern clinical practice.