title: Efficacy, persistence and vector susceptibility to pirimiphos-methyl (Actellic 300CS) insecticide for indoor residual spraying in Zanzibar.
abstract: BACKGROUND
  Indoor residual spraying (IRS) of households with insecticide is a principal malaria vector control intervention in Zanzibar. In 2006, IRS using the pyrethroid lambda-cyhalothrine was introduced in Zanzibar. Following detection of pyrethroid resistance in 2010, an insecticide resistance management plan was proposed, and IRS using bendiocarb was started in 2011. In 2014, bendiocarb was replaced by pirimiphos methyl. This study investigated the residual efficacy of pirimiphos methyl (Actellic 300CS) sprayed on common surfaces of human dwellings in Zanzibar.
  
  
  METHODS
  The residual activity of Actellic 300CS was determined over 9 months through bioassay tests that measured the mortality of female Anopheles mosquitoes, exposed to sprayed surfaces under a WHO cone. The wall surfaces included; mud wall, oil or water painted walls, lime washed wall, un-plastered cement block wall and stone blocks. Insecticide susceptibility testing was done to investigate the resistance status of local malaria vectors against Actellic 300CS using WHO protocols; Anopheline species were identified using PCR methods.
  
  
  RESULTS
  Baseline tests conducted one-day post-IRS revealed 100% mortality on all sprayed surfaces. The residual efficacy of Actellic 300CS was maintained on all sprayed surfaces up to 8 months post-IRS. However, the bioassay test conducted 9 months post-IRS showed the 24 h mortality rate to be ≤80% for lime wash, mud wall, water paint and stone block surfaces. Only oil paint surface retained the recommended residual efficacy beyond 9 months post-IRS, with mortality maintained at ≥97 %. Results of susceptibility tests showed that malaria vectors in Zanzibar were fully (100%) susceptible to Actellic 300CS. The predominant mosquito vector species was An. arabiensis (76.0%) in Pemba and An. gambiae (83.5%) in Unguja.
  
  
  CONCLUSIONS
  The microencapsulated formulation of pirimiphos methyl (Actellic 300CS) is a highly effective and appropriate insecticide for IRS use in Zanzibar as it showed a relatively prolonged residual activity compared to other products used for the same purpose. The insecticide extends the residual effect of IRS thereby making it possible to effectively protect communities with a single annual spray round reducing overall costs. The insecticide proved to be a useful alternative in insecticide resistance management plans.
authors.affiliation: Zanzibar Malaria Elimination Programme, Zanzibar, Tanzania. kahajim@yahoo.com.
authors.forename: Khamis A
authors.initials: KA
authors.lastname: Haji
authors.affiliation: RTI International, Dar es Salaam, Tanzania. narjis.thawer@gmail.com.
authors.forename: Narjis G
authors.initials: NG
authors.lastname: Thawer
authors.affiliation: Zanzibar Malaria Elimination Programme, Zanzibar, Tanzania. khatib562@yahoo.com.
authors.forename: Bakari O
authors.initials: BO
authors.lastname: Khatib
authors.affiliation: Zanzibar Malaria Elimination Programme, Zanzibar, Tanzania. jhmach@gmail.com.
authors.forename: Juma H
authors.initials: JH
authors.lastname: Mcha
authors.affiliation: RTI International, Dar es Salaam, Tanzania. Abdullah.salum@yahoo.com.
authors.forename: Abdallah
authors.initials: A
authors.lastname: Rashid
authors.affiliation: Zanzibar Malaria Elimination Programme, Zanzibar, Tanzania. busudi@gmail.com.
authors.forename: Abdullah S
authors.initials: AS
authors.lastname: Ali
authors.affiliation: Liverpool School of Tropical Medicine, Liverpool, UK. Christopher.jones@rothamsted.ac.uk.
authors.forename: Christopher
authors.initials: C
authors.lastname: Jones
authors.affiliation: Liverpool School of Tropical Medicine, Liverpool, UK. j.e.bagi@pgr.reading.ac.uk.
authors.forename: Judit
authors.initials: J
authors.lastname: Bagi
authors.affiliation: RTI International, Dar es Salaam, Tanzania. smagesa@rti.org.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Magesa
authors.affiliation: RTI International, Dar es Salaam, Tanzania. mmohamed@rti.org.
authors.forename: Mahdi M
authors.initials: MM
authors.lastname: Ramsan
authors.affiliation: RTI International, Dar es Salaam, Tanzania. igarimo@nb.rti.org.
authors.forename: Issa
authors.initials: I
authors.lastname: Garimo
authors.affiliation: President's Malaria Initiative/United States Agency for International Development, Dar es Salaam, Tanzania. ggreer@usaid.gov.
authors.forename: George
authors.initials: G
authors.lastname: Greer
authors.affiliation: RTI International, Washington DC, USA. rreithinger@rti.org.
authors.forename: Richard
authors.initials: R
authors.lastname: Reithinger
authors.affiliation: RTI International, Dar es Salaam, Tanzania. jngondi@rti.org.
authors.forename: Jeremiah M
authors.initials: JM
authors.lastname: Ngondi
mesh_terms: D000336:Aerosols / Q000494:pharmacology*; D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000502:physiology; D001681:Biological Assay; D005191:Family Characteristics; D006801:Humans; D007306:Insecticides / Q000494:pharmacology*; D009032:Mosquito Control / Q000379:methods; D009946:Organothiophosphorus Compounds / Q000494:pharmacology*; D016019:Survival Analysis; D013636:Tanzania
chemical_list: D000336:Aerosols; D007306:Insecticides; D009946:Organothiophosphorus Compounds; C014153:pirimiphos methyl