title: The impact of different sprayable surfaces on the effectiveness of indoor residual spraying using a micro encapsulated formulation of lambda-cyhalothrin against Anopheles gambiae s.s.
abstract: BACKGROUND
  The type of sprayable surface impacts on residual efficacy of insecticide used in indoor residual spraying (IRS). However, there is limited data on common types of wall surfaces sprayed in Zanzibar and mainland Tanzania where IRS began in 2006 and 2007 respectively. The study investigated residual efficacy of micro-encapsulated lambda-cyhalothrin sprayed on common surfaces of human dwellings and domestic animal shelters in Zanzibar and mainland Tanzania.
  
  
  METHODS
  An experimental hut was constructed with different types of materials simulating common sprayable surfaces in Zanzibar and mainland Tanzania. Surfaces included cement plastered wall, mud-daub, white-wash, wood, palm-thatch, galvanized iron-sheets, burnt-bricks, limestone and oil-paint. The World Health Organization (WHO) procedure for IRS was used to spray lambda-cyhalothrin on surfaces at the dose of 20-25 mg/m(2). Residual efficacy of insecticide was monitored through cone bioassay using laboratory-reared mosquitoes; Kisumu strain (R-70) of Anopheles gambiae ss. Cone bioassay was done every fortnight for a period of 152 days. The WHO Pesticide Evaluation Scheme (WHOPES) threshold (80% mortality) was used as cut-off point for acceptable residual efficacy.
  
  
  RESULTS
  A total of 5,800 mosquitoes were subjected to contact cone bioassay to test residual efficacy of lambda-cyhalothrin. There was a statistically significant variation in residual efficacy between the different types of wall surfaces (r = 0.24; p < 0.001). Residual efficacy decreased with increasing pH of the substrate (r = -0.5; p < 0.001). Based on WHOPES standards, shorter residual efficacy (42-56 days) was found in wall substrates made of cement, limestone, mud-daub, oil paint and white wash. Burnt bricks retained the residual efficacy up to 134 days while galvanized iron sheets, palm thatch and wood retained the recommended residual efficacy beyond 152 days.
  
  
  CONCLUSIONS
  The study revealed a wide variation in residual efficacy of micro encapsulated formulation of lambda-cyhalothrin across the different types of wall surfaces studied. In areas where malaria transmission is bimodal and wall surfaces with short residual efficacy comprise > 20% of sprayable structures, two rounds of IRS using lambda-cyhalothrin should be considered. Further studies are required to investigate the impact of sprayable surfaces on residual efficacy of other insecticides commonly used for IRS in Zanzibar and mainland Tanzania.
authors.affiliation: RTI International, Dar es salaam, Tanzania. mmutagahywa@yahoo.com.|Department of Zoology and Wildlife Conservation College of Natural and Applied Sciences, University of Dar es salaam, Dar es salaam, Tanzania. mmutagahywa@yahoo.com.
authors.forename: Joshua
authors.initials: J
authors.lastname: Mutagahywa
authors.affiliation: Nelson Mandela African Institute of Science and Technology, Arusha, Tanzania. jasperijumba@hotmail.com.
authors.forename: Jasper N
authors.initials: JN
authors.lastname: Ijumba
authors.affiliation: Department of Zoology and Wildlife Conservation College of Natural and Applied Sciences, University of Dar es salaam, Dar es salaam, Tanzania. pratap@udsm.ac.tz.
authors.forename: Harish B
authors.initials: HB
authors.lastname: Pratap
authors.affiliation: Swiss Tropical and Public Health Institute, Dar es salaam, Tanzania. fabrizio.molteni@netcell.org.|National Malaria Control Program, Ministry of health and Social Welfare, Dar es salaam, Tanzania. fabrizio.molteni@netcell.org.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Molteni
authors.affiliation: Sengerema Health Institute, Sengerema, Tanzania. eradiusmugalurafrances@gmail.com.
authors.forename: Frances E
authors.initials: FE
authors.lastname: Mugarula
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: United States Agency for International Development, Abuja, Nigeria. jkafuko@yahoo.com.
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Kafuko
authors.affiliation: School of Public Health, Catholic University of Health and Allied Sciences, Mwanza, Tanzania. elcnyanza@gmail.com.
authors.forename: Elias C
authors.initials: EC
authors.lastname: Nyanza
authors.affiliation: RTI International, Dar es salaam, Tanzania. smwaipape@nb.rti.org.
authors.forename: Osia
authors.initials: O
authors.lastname: Mwaipape
authors.affiliation: RTI International, Dar es salaam, Tanzania. jrutta@nb.rti.org.
authors.forename: Juma G
authors.initials: JG
authors.lastname: Rutta
authors.affiliation: National Malaria Control Program, Ministry of health and Social Welfare, Dar es salaam, Tanzania. dismas@yahoo.com.
authors.forename: Charles D
authors.initials: CD
authors.lastname: Mwalimu
authors.affiliation: RTI International, North Carolina, USA. indong@rti.org.
authors.forename: Isaiah
authors.initials: I
authors.lastname: Ndong
authors.affiliation: RTI International, Washington, DC, USA. reithinger@rti.org.
authors.forename: Richard
authors.initials: R
authors.lastname: Reithinger
authors.affiliation: RTI International, Dar es salaam, Tanzania. narjis.thawer@gmail.com.
authors.forename: Narjis G
authors.initials: NG
authors.lastname: Thawer
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 / Q000008:administration & dosage*; D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000502:physiology*; D001681:Biological Assay; D006798:Housing; D006801:Humans; D007306:Insecticides / Q000008:administration & dosage*; D008962:Models, Theoretical; D009570:Nitriles / Q000008:administration & dosage*; D011722:Pyrethrins / Q000008:administration & dosage*; D013499:Surface Properties; D016019:Survival Analysis; D013636:Tanzania; D016896:Treatment Outcome
chemical_list: D000336:Aerosols; D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C037304:cyhalothrin