New chemical formulation fights resistance in malaria bed nets
During a trial in Uganda, long-lasting insecticidal nets, or LLINs, augmented with a chemical called piperonyl butoxide were more effective in reducing the prevalence of malaria parasites than conventional insecticidal nets treated with just pyrethroid, according to results presented at the American Society of Tropical Medicine and Hygiene Annual Meeting.
“LLINs are the cornerstone of malaria control in Africa, but their effectiveness is threatened by pyrethroid resistance,” Sarah Staedke, MD, PhD, DTM&H, professor of malaria and global health at the London School of Hygiene & Tropical Medicine, told Healio. “Newer LLINs combine pyrethroid insecticides with a synergist, piperonyl butoxide (PBO), which can block the mosquito’s defense against pyrethroids and at least partially restore susceptibility to the insecticide.”
Staedke and colleagues examined parasite prevalence in over 23,000 children aged 2 to 10 years old — covering 40% of Uganda. They randomly assigned 104 health subdistricts, or clusters, to use either PermaNet or Oylset Plus brand nets with or without PBO. In the PBO group, 31 clusters were assigned PermaNet and 18 were assigned Oylset Plus, whereas 39 were assigned PermaNet and 13 were assigned Oylset in the non-PBO group. They conducted cross-sectional surveys in 50 randomly selected households per cluster at 6, 12 and 18 months, with a subset of 10 households per cluster randomly selected for entomology surveys.
Parasite prevalence was 10.7% in the PBO group and 14.5% in the non-PBO group, an adjusted prevalence ratio (PR) of 0.74 (95% CI, 0.62-0.87) at 6 months. Results were similar at 12 months (10.6% vs. 13%; PR = 0.73; 95% CI, 0.63-0.85) and 18 months (11.8% vs. 14%; PR = 0.84; 95% CI, 0.72-0.98).
“There are also potential improvements to net design,” Martin Donnelly, MSc, PhD, professor of evolutionary genetics at the Liverpool School of Tropical Medicine, told Healio. “At LSTM, researchers are using high-resolution video capture to investigate mosquito behavior at the net interface and have used this information to develop new net shapes.”
Donnelly also believes the dual-compound strategy could potentially be applied in other areas, like house screening, and potentially aid in mitigating other vector-borne diseases like dengue.
“This innovative trial, embedded within a national LLIN distribution campaign, serves as a paradigm for future assessment of malaria control interventions,” Staedke said. “Future studies should investigate the cost-effectiveness of PBO LLINs, the effectiveness of new-generation LLINs, including those with two active ingredients, and approaches for integrating LLINs with [indoor residual spraying] and other new malaria control tools, as these become available.” – by Eamon Dreisbach
Staedke SG, et al. LLIN Evaluation in Uganda Project (LLINEUP) – Effect of long-lasting insecticidal nets (LLINs) with, and without, piperonyl butoxide on malaria indicators in Uganda: a cluster-randomised trial embedded in a national LLIN distribution campaign. Presented at: ASTMH Annual Meeting; Nov. 20-24, 2019; National Harbor, Maryland.
Disclosures: Donnelly and Staedke report no relevant financial disclosures.