Reduced exposure to malaria vectors following indoor residual spraying of pirimiphos-methyl in a high-burden district of rural Mozambique with high ownership of long-lasting insecticidal nets: entomological surveillance results from a cluster-randomized trial

• Published in: Malaria journal 2021-01, Vol.20 (1), p.54-54, Article 54
• Main Authors: Wagman, Joseph M, Varela, Kenyssony, Zulliger, Rose, Saifodine, Abuchahama, Muthoni, Rodaly, Magesa, Stephen, Chaccour, Carlos, Gogue, Christelle, Tynuv, Kenzie, Seyoum, Aklilu, Dengela, Dereje, Saúte, Francisco, Richardson, Jason H, Fornadel, Christen, Linton, Yvonne-Marie, Slutsker, Laurence, Candrinho, Baltazar, Robertson, Molly
• Format: Article
• Language: English
• Subjects: 3GIRS; An. funestus; Aquatic insects; Bioassays; Biting; Cluster-randomized trial; Collections; Cypermethrin; Distribution; Feeds; Global health; Health surveillance; Households; Human diseases; Indoor environments; Indoor residual spraying; Insecticides; Light; Light traps; Malaria; Mortality; Mosquitoes; Nets; New products; Pirimiphos-methyl; Prevention; Public health; Pyrethroid resistance; Pyrethroids; Risk factors; Spraying; Statistical analysis; Testing; Vector-borne diseases; Vectors; Villages
• ISSN: 1475-2875; 1475-2875
• DOI: 10.1186/s12936-021-03583-8

The need to develop new products and novel approaches for malaria vector control is recognized as a global health priority. One approach to meeting this need has been the development of new products for indoor residual spraying (IRS) with novel active ingredients for public health. While initial results showing the impact of several of these next-generation IRS products have been encouraging, questions remain about how to best deploy them for maximum impact. To help address these questions, a 2-year cluster-randomized controlled trial to measure the impact of IRS with a microencapsulated formulation of pirimiphos-methyl (PM) in an area with high ownership of long-lasting insecticidal nets (LLINs) was conducted in a high-transmission district of central Mozambique with pyrethroid resistant vectors. Presented here are the results of the vector surveillance component of the trial. The 2 year, two-armed trial was conducted in Mopeia District, Zambezia Province, Mozambique. In ten sentinel villages, five that received IRS with PM in October-November 2016 and again in October-November 2017 and five that received no IRS, indoor light trap collections and paired indoor-outdoor human landing collections catches (HLCs) were conducted monthly from September 2016 through October 2018. A universal coverage campaign in June 2017, just prior to the second spray round, distributed 131,540 standard alpha-cypermethrin LLINs across all study villages and increased overall net usage rates in children under 5 years old to over 90%. The primary malaria vector during the trial was Anopheles funestus sensu lato (s.l.), and standard World Health Organization (WHO) tube tests with this population indicated variable but increasing resistance to pyrethroids (including alpha-cypermethrin, from > 85% mortality in 2017 to 7% mortality in 2018) and uniform susceptibility to PM (100% mortality in both years). Over the entire duration of the study, IRS reduced An. funestus s.l. densities by 48% (CI 33-59%; p