Chancroid is a sexually transmitted genital ulcer disease (GUD) caused by the gram-negative bacillus Haemophilus ducreyi. Chancroid is characterized by the presence of painful ulcers (see image below) and inflammatory inguinal adenopathy. 
Chancroid is often referred to as a soft chancre because the lesions are usually not indurated. In contrast, a syphilitic chancre is nontender and indurated. The identification of the causative agent of chancroid was first reported in 1889 by August Ducrey, following experiments in which he autoinoculated patients' forearms with pus from their genital ulcers. [2, 3, 4]
H ducreyi produces a potent cytolethal distending toxin, which is an important virulence factor in the pathogenesis of chancroid, probably contributing to both the generation and the slow healing of ulcers. [5, 6, 7, 8]
H ducreyi contains a fimbrialike protein (Flp) operon that encodes proteins that contribute to adherence and pathogenesis. The production and secretion of 3 Flp proteins, Flp1, Flp2, Flp3, has been demonstrated to contribute to microcolony formation and attachment to human foreskin fibroblasts cells in vitro.  In a small human trial, injection of a deletion mutant that lacked expression of all 3 Flp proteins into volunteers demonstrated significantly reduced size of papule formation, as well as pustule formation rate. 
Chancroid, or soft chancre, facilitates human immunodeficiency virus (HIV) transmission. The chemokine receptors CCR5 and CXCR4 belong to the class of 7 transmembrane G-protein–coupled receptors, and their natural ligands are key players in the recruitment of immune cells to sites of inflammation. CCR5 and CXCR4 are the 2 main co-receptors essential for HIV entry. Macrophages in chancroid lesions have significantly increased expression of CCR5 and CXCR4 compared with peripheral blood cells, and CD4 T cells have significant up-regulation of CCR5. The beta-chemokine RANTES (regulated on activation, normal T cell expressed and secreted) are important ligands for CCR5. RANTES is present throughout the papular and pustular stages of chancroid infection but is not present in uninfected control skin. 
Host polymorphisms in TLR9 and IL10 may alter manifestations of the disease. 
Together with the disruption of mucosal and skin barriers, the presence of cells with up-regulated HIV-1 co-receptors in H ducreyi –infected lesions provides an environment that facilitates the acquisition of HIV-1 infection. Effective and early treatment of genital ulceration, and chancroid in particular, may help to control the spread of HIV infection in tropical countries  ; however, at present, evidence to determine whether this will significantly reduce the risk of HIV acquisition is insufficient. [14, 15]
Chancroid is rarely reported in the United States, but regional outbreaks and some endemic transmission occur, principally among migrant farm workers and poor inner-city residents. 
Because of a lack of readily available, accurate diagnostic tests, the global incidence of chancroid is unknown. An estimated 6 million cases of chancroid occur each year. Chancroid is common in many of the world's poorest regions such as areas of Africa, Asia, and the Caribbean. These regions also have some of the highest rates of HIV infection in the world, and chancroid is common in all 18 countries where adult HIV prevalence surpasses 8%. In addition to regional outbreaks, individual cases are reported sporadically in the developed world, usually in individuals who have recently returned from chancroid-endemic areas or occasionally within the context of localized urban outbreaks, which may be associated with commercial sex work.
Males develop chancroid most often, with a male-to-female ratio of 3-25:1.  Uncircumcised men develop chancroid more often than circumcised men.  Patients who are uncircumcised do not respond to treatment as well as those who are circumcised. [19, 20] Chancroid is more common in heterosexual men. 
Female prostitutes, either with active disease in the form of genital ulcers or as asymptomatic carriers, are an important reservoir for chancroid infection.
Chancroid is most prevalent in sexually active and promiscuous males, with a mean patient age of 30 years.
The prognosis is excellent if chancroid is treated properly and if no co-infection with HIV is present. As many as 5% of patients have a chancroid relapse and usually respond to a repeat course of their original therapy. No adverse effects of chancroid on pregnancy outcome have been reported.
Chancroid produces painful ulcers on the genitals, often (50%) associated with unilateral tender inguinal lymphadenitis (ie, a bubo). Left untreated, the buboes can form fluctuant abscesses that spontaneously rupture, resulting in a nonhealing ulcer.
Chancroid has been shown to be a major cofactor in the transmission of HIV-1 infection.  This relationship has been especially significant in the heterosexual spread of HIV in Africa. [13, 23] Chancroid-infected patients who have HIV should be monitored closely because they are more likely to experience treatment failure and to have ulcers that heal slowly.
The patient should be strongly advised to avoid sexual contacts while the ulcers are open because they are highly infectious and may cause a community outbreak.
Patients should be advised to avoid prostitutes, to use condoms, and to avoid having multiple partners.
Cocaine and alcohol abuse should be addressed because both contribute to higher rates of the disease.
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