August 20, 2018
2 min read

Dual-treated bed nets enhance protection against malaria in children

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Long-lasting insecticidal bed nets treated with permethrin and pyriproxyfen were more effective against malaria than standard nets treated with permethrin alone, according to recent findings published in The Lancet.

The study showed that young children who used long-lasting insecticidal bed nets (LLINs) with the commonly used pyrethroid, permethrin, as well as pyriproxyfen, a chemical that reduces mosquito growth and reproduction (PPF; Olyset Duo, Sumitomo Chemical), were 12% less likely to develop clinical malaria and 52% less likely to develop moderate anemia than children who used standard LLINs.

“This study is important because malaria control in sub-Saharan Africa has stalled, partly because the mosquitoes are adapting and becoming resistant to the pyrethroid insecticides used for treating the old bed nets,” Steve W. Lindsay, PhD, professor in the department of biosciences at Durham University, said in a news release. “Malaria still kills a child every 2 minutes, so we need to keep working to find the best ways to stop this from happening.”

Lindsay and colleagues assessed the efficacy of the dual-treated LLINs in 40 rural clusters covering 91 villages in Burkina Faso, where mosquitoes are becoming increasingly resistant to pyrethroids. The researchers performed a two-group, step-wedge, cluster-randomized controlled trial in which standard LLINs were replaced over time in the clusters with the PPF-treated LLINs. Approximately 50 children in each cluster were evaluated for mosquito bites, clinical malaria and anemia.

By the end of the 2-year trial, 99% of children in the clusters slept under a bed net. The incidence of clinical malaria was two episodes per child-year among participants using the standard LLIN and one and a half episodes per child-year among those using the PPF-treated LLINs, representing a 12% reduction in cases (incidence rate ratio = 0.88; 95% CI, 0.77-0.99). The incidence of moderate anemia was also lower among children using the PPF-treated LLINs (OR = 0.48; 95% CI, 0.24-0.96).

“The reduction in moderate anemia is clinically relevant because anemia due to malaria is a major cause of mortality in children younger than 2 years,” the researchers wrote.

The entomological inoculation rate, defined as the number of infective mosquito bites, was 85 (95% CI, 63-108) bites per transmission season in the standard LLIN group and 42 (95% CI, 32-52) bites per transmission season in the PPF-treated LLIN group, representing a 51% reduction.

“This trial provides, for the first time, evidence of added benefit from an LLIN treated with a nonpyrethroid insecticide in combination with a pyrethroid,” John E. Gimnig, PhD, of the CDC’s Division of Parasitic Diseases and Malaria, and Eric Ochomo, PhD, of the Center for Global Health Research at Kenya Medical Research Institute, wrote in a related editorial.

Despite its efficacy, Gimnig and Ochomo warned that the higher cost of the dual-treated LLINs may reduce coverage. However, they noted that donors such as the U.S. President’s Malaria Initiative and the Global Fund to Fight AIDS, Tuberculosis and Malaria, might invest in the PFF-treated LLINs, and that costs may decrease over time with competition and economies of scale.

“Although the [Global Plan for Insecticide Resistance Management] is in need of updating, its recommendation to use nets with nonpyrethroid active ingredients as soon as they become available is suddenly relevant,” they wrote. “They are available now and it is time to use them. However, we must do so judiciously to maintain the efficacy of these new active ingredients and to avoid the crisis we have faced with pyrethroid resistance.” – by Stephanie Viguers

Disclosures: The authors report no relevant financial disclosures.