January 03, 2020
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WHO schistosomiasis control, elimination targets reached sooner than expected

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WHO goals for schistosomiasis control and elimination are often achieved sooner than expected, according to a study published in the New England Journal of Medicine.

In particular, WHO programs in areas with low endemic levels of disease at baseline were more likely to achieve both the control and elimination targets than the programs in areas with moderate to high endemic levels of disease at baseline.

Schistosomiasis is a parasitic neglected tropical disease that is estimated to currently infect more than 140 million persons. Ninety percent of the disease burden is in sub-Saharan Africa, where the main species that cause schistosomiasis in humans are Schistosoma mansoni (intestinal schistosomiasis) and S. haematobium (urogenital schistosomiasis), which are transmitted through feces and urine, respectively,” Arminder K. Deol, PhD, of the Schistosomiasis Control Initiative and the London Centre for Neglected Tropical Disease Research, and colleagues wrote.

The WHO strategy to control schistosomiasis involved the dissemination of therapy primarily to school-age children 5 to 15 years of age, the group with the highest infection burden, who can be reached effectively through schools. An infection incidence below 10% would involve preventive chemotherapy administration every 3 years; an infection rate of 10% to 49% would require treatment every 2 years and an infection rate of 50% or greater would require annual treatment.

“The initial success of disease control in some countries has led to the more ambitious WHO vision of ‘a world free of schistosomiasis,’” Deol and colleague continued. “The WHO thus set goals for controlling schistosomiasis morbidity by 2020 and achieving the elimination of schistosomiasis as a public health problem ... by 2025 in all countries where schistosomiasis is endemic.”

To evaluate WHO guidelines and the likelihood of reaching these goals, researchers gathered data from nine national schistosomiasis control programs in eight countries in sub-Saharan African and in Yemen. They evaluated the programs by schistosome species, number of treatment rounds, overall incidence and the frequency of heavy-intensity infection.

Infection intensity in all countries studied declined following the first round of treatment to below or within 0.8 percentage points of the 5% prevalence for the heavy-intensity threshold for S. mansoni infection control and within 3.3 percentage points for S. haematibium infection control. Researchers also found that treatment reduced the prevalence of heavy-intensity infection by both species to below 5% in all country programs except that in Niger (5.4%; 95% CI, 2.0 to 13.8), “which only marginally missed the metric for S. haematibium infection in the first treatment round,” the researchers wrote.

The ‘key messages’ of the study demonstrate that “countries often achieve disease control after very few treatment rounds,” Deol and colleagues concluded. In addition, “the universal timeline currently recommended is not appropriate for all programs and will be affected by baseline endemicity, schistosome species, and the context-specific relationship between infection and morbidity, among other extraneous factors.” – by Caitlyn Stulpin

Disclosures: The authors report not relevant financial disclosures.