H. ducreyi causes
chancroid, a common cause of genital ulcer in Africa, Southeast Asia,India, and
Latin America. Occasional outbreaks in North America have most often been
associated with the exchange of sex for drugs or money. The typical lesion is a
tender papule on the genitalia that develops into a painful ulcer with sharp
margins. Satellite le-sions may develop by autoinfection, and regional
lymphadenitis is common. The incuba-tion period is usually short (2 to 5 days).
The lack of induration around the ulcer has caused the primary lesion to be
called “soft chancre” to distinguish it from the primary syphilitic chancre,
which is typically indurated and painless. The presence of open genital sores
due to H. ducreyi enhances the risk
of transmission of HIV either by providing a portal of entry or by the
recruitment of CD4+ cells to the site. This may contribute to the heterosexual
spread of acquired immunodeficiency syndrome (AIDS) on the African con-tinent,
where chancroid is common. Candidate H.
ducreyi virulence factors include adhe-sive pili, resistance to phagocytosis,
and complement-mediated killing. A seeming lack of immunity may be due to the
action of a toxin (cytolethal distending toxin) on T cells.
The specific diagnosis of H. ducreyi infection is difficult. Although the organism grows on
chocolate agar, it does so slowly and other organisms present in the genital
flora are apt to overgrow the plates. A special medium incorporates vancomycin
as a selective agent, but few laboratories in the United States have it on
hand. Chancroid is effectively treated with azithromycin, ceftriaxone, or