A study published in The Lancet tested LLINs with new active ingredients to evaluate their success against malaria carriers. The study found that LLINs treated with the insecticides chlorfenapyr and pyrethroid reduced malaria infections by almost half. “Malaria remains a huge problem in sub-Saharan Africa and is one of the leading causes of death in Tanzania,” said Jacklin F. Mosha, PhD, the study’s lead author. “We urgently need new interventions to restore control efforts and protect young people from this deadly disease. “These exciting results underscore that we have another effective tool for controlling malaria.” The researchers conducted a randomized trial in groups in Misungwi, Tanzania, an area in sub-Saharan Africa with a high incidence of malaria among children. The groups were villages of at least 119 households with children aged 6 months-14 years living in the central area. The groups received 1 of the 4 LLIN types treated with α-cypermethrin alone (pyrethroid control group only). pyriproxyfen and α-cypermethrin (pyriproxyfen group). chlorfenapyr and α-cypermethrin (chlorfenapyr group). or the synergistic piperonylbutoxide and permethrin (piperonylbutoxide group). At least 1 LLIN was given to every 2 people. The researchers collected data on the prevalence of malaria by administering synchronous surveys to randomly selected households in each group. Children 6 months-14 years were tested for malaria infection with Plasmodium falciparum through rapid diagnostic testing. Each of the active duel LLINs was compared to standard LLINs with pyrethroids only. The main outcome of the study was the prevalence of malaria at 24 months after distribution of LLIN. Side effects included the cost-effectiveness of LLINs with two active ingredients. From May 11 to July 2, 2018, researchers recruited 39,307 households, divided into 84 groups. A total of 147230 LLINs were distributed among households from 26 January to 28 January 2019. LLIN use was reported in 72.1% of survey participants 3 months after distribution, which decreased by a response rate of 40.9% in 24 months after delivery. Malaria infection at 24 months after LLIN dispersal was 45.8% in the pytheroid group alone, 37.5% in the pyriproxyphene group, 40.7% in the piperonylbutoxide group and 25.6% in the chlorophenapyr group. The most effective LLINs were chlorfenapyr and the most commonly reported side effects were skin irritation or hallucinations. The study authors noted that poor fabric quality and durability of the active ingredients of piperonylbutoxide and pyrroxyphene LLIN may have reduced their effectiveness. Overall, LLINs treated with chlorfenapyr and pytheroid reduced malaria infections by 43% in the first year and 37% in the second year. Chlorfenapyr works differently from standard LYLs that contain only pteroids, causing wing muscle cramps that prevent mosquitoes from flying and thus biting the hosts. “What really struck us for a long time was that in daily trials chlorfenapyr was not very toxic to mosquitoes,” said Mark Rowland, PhD, author of the study. “But at night, when malaria mosquitoes fly naturally over the treated net, a serious case of muscle cramps occurs, so it bends and falls where it is likely to be carried by the wiping ants. No other mosquito repellent works this way and because of its unique mode of action it kills all species of mosquitoes that have developed resistance to other insecticides. “It must have a long future.” The researchers concluded that after 2 years, chlorfenapyr LLINs provided better protection against malaria than pyrethroid-only LLINs in an area with pyrethroid-resistant mosquitoes. However, they noted that switching to chlorfenapyr nets should be done with caution to prevent mosquitoes from developing resistance again. “The mass escalation of typical LLIN pyrethroids 10-20 years ago has led to the rapid spread of pyrethroid resistance. “The challenge now is to maintain the effectiveness of chlorfenapyr by developing rational resistance management strategies,” said Natacha Protopopoff, PhD, lead researcher.
