Historical background and epidemiology
The bacterium Haemophilus ducreyi has a rich history of study: the microorganism was first isolated by O.V. Petersen in 1887, and already in 1890 it was described in detail by A. Ducrey, whose name forms the basis of the species epithet.
The infection belongs to the group of classical sexually transmitted diseases. The human patient is the sole source of infection. Transmission occurs predominantly through contact. In the vast majority of cases, the sexual route of transmission is realized, although in rare situations contact-household transmission is also possible. Epidemiological foci of the disease nowadays are most frequently registered in regions of Africa and South America.
Clinical presentation and pathogenesis
The incubation period for Haemophilus ducreyi infection is relatively short: on average it lasts from 3 to 5 days, although the first clinical signs may manifest as early as the first day after contact with the pathogen.
The pathological process is most often localized in the genital area. However, due to the propensity for autoinoculation (transfer of the pathogen by hands to other parts of the body), extragenital lesions may occur.
Main morphological features of chancroid:
- Formation of a soft ulcer with uneven, rough edges.
- Development of significant edema of the surrounding soft tissues.
- Appearance of regional lymphadenitis — the lymph nodes noticeably increase in size and become sharply painful.
The course of the infection is characterized by slow healing of the ulcerative defects. In an unfavorable scenario, there is a high risk of generalization of the process, when the pathogen enters the systemic bloodstream.
Differential diagnosis
An essential stage is the differentiation of chancroid from the hard chancre, which is the classic manifestation of primary syphilis.
| Sign | Chancroid (H. ducreyi) | Hard chancre (syphilis) |
|---|---|---|
| Painfulness | Ulcer is sharply painful upon palpation | Ulcer is painless |
| Bleeding | Pronounced bleeding is characteristic | Bleeding is not typical |
| Consistency | Soft base of the ulcer | Hard (cartilaginous) base |
Laboratory diagnostics
To confirm the diagnosis, discharge from the bottom and edges of the ulcer is used as the test material.
- Microscopic method. Gram staining of smears reveals small Gram-negative rods. It is important to consider that Haemophilus ducreyi is often present in association with abundant concomitant pyogenic microflora.
- Culture (bacteriological) method. Isolation of a pure culture requires the creation of specific conditions. The pathogen requires X-factor (hemin), while V-factor is not required for its growth. Inoculation is performed on chocolate agar supplemented with vancomycin — this antibiotic is necessary to suppress the growth of concomitant flora. Incubation is carried out at 33 °C in an atmosphere enriched with CO₂. Characteristic grayish colonies without signs of hemolysis grow on Petri dishes.
- Molecular genetic method. PCR diagnostics is used for rapid and accurate identification of the pathogen's DNA in clinical material.
Principles of treatment and prevention
Since specific prevention (vaccination) against chancroid has not been developed to date, and post-infection immunity is not produced, timely antibiotic therapy plays a key role.
Drugs of choice to eliminate the infection:
- Ceftriaxone;
- Co-trimoxazole;
- Erythromycin.
The standard course of antibacterial therapy lasts 2 weeks.
Antibiotic resistance issue: It is important to remember that drugs from the tetracycline, sulfonamide, and penicillin groups are not used in modern clinical practice. This is due to the high resistance of circulating strains of Haemophilus ducreyi to these antibiotics.
Briefly: answers to topical questions
What is the morphology and respiration type of Haemophilus ducreyi?
The causative agent Haemophilus ducreyi represents small Gram-negative rods that are classified as facultative anaerobes based on their respiration type.
Morphological features of the bacterium:
- Size and shape — Gram-negative rods (0.5–0.7 × 2–3 µm), often located in smears in association with pyogenic flora.
- Motility — non-motile, as they lack flagella.
- Spore formation — do not form spores.
- Capsule formation — do not form capsules.
To remember the microbe's growth factor requirements, use the phrase: "Chancroid is an EX-clusive infection" (only X-factor is required, and V-factor is not needed).
Class and exam questions
Can you get infected with chancroid again?
Yes, it is possible. Protective immunity is not developed after the infection, so reinfection is possible.
What is the main clinical difference between chancroid and hard chancre?
Unlike the hard chancre in syphilis, the ulcer in Haemophilus ducreyi infection has a soft base, bleeds characteristically, and is sharply painful upon palpation.
Why is vancomycin added when plating on nutrient media?
Vancomycin is added to chocolate agar to suppress the growth of concomitant pyogenic flora, which is present in excess in the ulcer discharge and can inhibit the growth of Haemophilus ducreyi.
What else to study on this topic
- Mechanisms of antibiotic resistance development in Haemophilus ducreyi
- Features of autoinoculation and extragenital localization of ulcers
- Pathogenesis of ulcer defect formation and the role of toxins
- Detailed algorithm for differential diagnosis of genital ulcers
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