Assessment of the virulence of H. ducreyi 35000HP vs. its derivative (FX548) containing a class II hgbA allele in humans

In addition to causing chancroid, Haemophilus ducreyi is a major cause of cutaneous ulcers in children. Despite mass drug administration with azithromycin, both class I and class II strains persist in ulcer-endemic regions, suggesting the need for a vaccine. The hemoglobin receptor (HgbA) is a leading vaccine candidate, but its efficacy in animal models is class-specific. As a prelude to evaluating HgbA vaccines in a human infection model, we tested whether a class 1 strain (35000HP) is as virulent as its derivative (FX548) containing a class II hgbA allele.