elsewhere. Increasing antibiotic resistance in gonococci (3) and H. ducreyi (4) has necessitated use of newer, more expensive, antimicrobials, a circumstance that can prohibit effective therapy in developing nations.

The importance of the bacterial STDs rests in part on their adverse effects on reproductive health. Both gonorrhea and genital chlamydia are major causes of salpingitis, ectopic pregnancy, and infertility. A sense of urgency for the control of these diseases has emerged recently because of evidence that they significantly increase the rate of HIV transmission between sexual partners (59). Genital ulcer disease is recognized as an important cofactor for HIV transmission (79) and H. ducreyi and T. pallidum are prominent causes of the genital ulcer syndrome. The effects of gonorrhea and genital chlamydia on HIV transmission (5, 6) may be due to microulceration (10) and increased local accumulation of activated lymphocytes and macrophages, with a corresponding increase in release of HIV into genital secretions (11).

Because of the apparent roles of bacterial STDs in HIV transmission, the World Health Organization has concluded that strategies to control HIV should include development of effective programs for control of bacterial STDs (12). Although experience in several nations shows this can be accomplished (at least temporarily) without vaccines (1, 2), experience in other nations, including the United States, suggests that this is a difficult task. Vaccines against bacterial STDs would improve the public health and would offer long-lasting and cost-effective solutions to common and expensive problems. The question is, can such vaccines be developed? This paper briefly reviews relevant progress in research towards this goal.

CHANCROID

Chancroid is an ulcerating cutaneous infection caused by H. ducreyi. Infection may persist for months without effective antibiotic therapy. In earlier times, clinicians inoculated normal skin with pus taken from genital ulcers of the patient, and development of typical ulcerating lesions after such inoculation was used to confirm the diagnosis of chancroid (13). Indeed, Ducrey (13) was able to serially propagate the infectious agent at least 15 times in the same individual, indicating that little or no immunity occurs in naturally acquired infection. Today, diagnosis is made by in vitro culture. A renewed surge of research interest occurred after recognition that H. ducreyi is a cofactor for HIV transmission (79), and factors involved in pathogenesis are beginning to be delineated (14).

The cardinal feature of chancroid is the development of ulcers on stratified squamous epithelium, which suggests that H. ducreyi might



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