Certain ulcer-causing bacteria have a natural reservoir

A study led by ISGlobal, an institution supported by the "la Caixa" Foundation, detects the presence of Haemophilus ducreyi, an ulcer-causing bacterium, on intact skin of asymptomatic children. It was also detected on flies and bedding from houses of children with ulcers. These results, published in Plos Neglected Tropical Diseases, could explain the persistence of a high prevalence of tropical ulcers despite one round of massive antibiotic administration.

Children living in rural communities of tropical countries often suffer skin ulcers that are mainly caused by infection with Haemophhilus ducreyi (causative agent of chancroid) and/or Treponema pallidum pertenue (causative agent of yaws).

Previous studies have shown that massive treatment with azithromycin is highly effective in reducing the number of yaws cases within treated communities, but the efficacy in reducing H. ducreyi infections is limited. Both infections are predominantly transmitted through direct contact with skin lesions on other children. However, the persistence of H. ducreyi ulcers after one round of massive antibiotic treatment raises the possibility that the bacteria may exist in a natural reservoir (e.g. skin colonization of asymptomatic carriers or contaminated surfaces).

In this study, the authors investigated the reasons underlying the limited effect of massive drug administration on H. ducreyi among communities in Lihir island, Papua New Guinea . They analysed potential environmental reservoirs and found the presence of H. ducreyi on skin of 21% of examined asymptomatic children and young adults (with no ulcers). In addition, they found DNA of H. ducreyi and T. p. pertenue on flies and bedsheets of households of children with ulcers, which could contribute to the spread of these organisms despite azithromycin treatment.

“Our results indicate that the persistence of ulcers caused by H. ducreyi after one round of massive drug administration is the result of the organism’s ubiquity in the environment” explains Oriol Mitjà, study coordinator. The authors argue that improved hygiene and repeated rounds of mass antibiotic administration could be necessary to control such a reservoir.

Each year, there are more than 100,000 cases of chronic tropical ulcers that represent a considerable physical and psychological burden for small children. In remote villages, up to 7% of children suffer from these ulcers, and therefore represent a serious public health problem.