Enzyme immunoassays (EIAs) for the detection of anti-Haemophilus ducreyi serum IgA, IgG, and IgM antibodies

Abstract

Background and objectives: Chancroid is a risk factor for heterosexually acquiring HIV. Controlling its spread may reduce HIV transmission.

Goal of the study: To develop EIAs for assessing antibody levels and for seroepidemiologic studies.

Study design: Anti-Haemophilus ducreyi IgA, IgG and IgM EIAs were standardized using a crude cocktail antigen. Evaluation was on sera from Kenya, Rwanda, Thailand and The Gambia. The two-tailed student's t test was used to compare results.

Results: The specificity of IgA was 97% (95% confidence interval (CI): 95-99%), of IgG was 92% (95% CI: 89-95%), and of IgM was 99% (95% CI: 98-100%). The sensitivity of IgA was 88% (95% CI: 83-93%), of IgG was 93% (95% CI:89-97%), and of IgM was 78% (95% CI:71-85%) in patients having an ulceration for more than eight days. Thus, 95% (95% CI:92-98%) of the chancroid patients were seropositive for at least one antibody type. The IgG and IgA EIAs were more sensitive in patients older than 24 years of age. Higher IgG rates were found in HIV infected chancroid patients.

Conclusion: The EIAs should be useful for studying the kinetics of antibody levels and the epidemiology of H. ducreyi infection.

PIP: In Belgium, the Department of Infection and Immunity of the Institute of Tropical Medicine in Antwerp modified an experimental enzyme immunoassay (EIA) for the detection of serum IgG to Hemophilus ducreyi to develop EIAs for detection of anti-H. ducreyi IgA and IgM antibodies. They tested the modified EIA on sera from people in Nairobi, Kenya; Kigali, Rwanda; Banjul, The Gambia; and Bangkok, Thailand, who had a sexually transmitted disease. The EIA was able to identify correctly those who did not have anti-H ducreyi IgA, IgG, and IgM antibodies in 97%, 92%, and 99% of cases, respectively. Among people with a genital ulceration for more than 8 days, it was able to identify correctly those who had IgA, IgG, and IgM antibodies in 88%, 93%, and 78% of cases, respectively. 95% of all culture-proven chancroid patients tested seropositive for at least 1 antibody type. The sensitivity of IgG and IgA EIAs was significantly enhanced in patients with culture-proven chancroid who were older than 24 years old (p .01). HIV seropositive people from Kigali who had culture-proven chancroid had higher anti-H. ducreyi IgG seropositivity rates (but not IgA and IgM seropositivity rates), than did HIV seronegative chancroid people from Kigali (p .05). The increased IgG seropositivity rate was not related to higher antibody titers, however, suggesting that HIV infection modifies the response to H. ducreyi. These results show that the 3 EIAs hold promise as a means to study the kinetics of antibodies and the epidemiology of chancroid.