title: Undesirable consequences of insecticide resistance following Aedes aegypti control activities due to a dengue outbreak.
abstract: BACKGROUND
  During a dengue outbreak with co-circulation of DENV-1 and -2 in the city of Boa Vista, one patient was diagnosed with DENV-4, a serotype supposed absent from Brazil for almost 30 years. The re-emergence of DENV-4 triggered the intensification of mechanical and chemical Aedes aegypti control activities in order to reduce vector density and avoid DENV-4 dissemination throughout the country.
  
  
  RESULTS
  Vector control activities consisted of (a) source reduction, (b) application of diflubenzuron against larvae and (c) vehicle-mounted space spraying of 2% deltamethrin to eliminate adults. Control activity efficacy was monitored by comparing the infestation levels and the number of eggs collected in ovitraps before and after interventions, performed in 22 Boa Vista districts, covering an area of ∼ 80% of the city and encompassing 56,837 dwellings. A total of 94,325 containers were eliminated or treated with diflubenzuron. The most frequently positive containers were small miscellaneous receptacles, which corresponded to 59% of all positive breeding sites. Insecticide resistance to deltamethrin was assessed before, during and after interventions by dose-response bioassays adopting WHO-based protocols. The intense use of the pyrethroid increased fourfold the resistance ratio of the local Ae. aegypti population only six months after the beginning of vector control. Curiously, this trend was also observed in the districts in which no deltamethrin was applied by the public health services. On the other hand, changes in the resistance ratio to the organophosphate temephos seemed less influenced by insecticide in Boa Vista.
  
  
  CONCLUSIONS
  Despite the intense effort, mosquito infestation levels were only slightly reduced. Besides, the median number of eggs in ovitraps remained unaltered after control activity intensification. The great and rapid increase in pyrethroid resistance levels of natural Ae. aegypti populations is discussed in the context of both public and domestic intensification of chemical control due to a dengue outbreak.
authors.affiliation: Laboratório de Transmissores de Hematozoários, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brazil.
authors.forename: Rafael
authors.initials: R
authors.lastname: Maciel-de-Freitas
authors.affiliation: Secretaria de Vigilância em Saúde, Ministério da Saúde, Brasília, Brazil.
authors.forename: Fernando Campos
authors.initials: FC
authors.lastname: Avendanho
authors.affiliation: Secretaria Estadual de Saúde de Roraima, Boa Vista, Brazil.
authors.forename: Rosangela
authors.initials: R
authors.lastname: Santos
authors.affiliation: Laboratório de Transmissores de Hematozoários, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brazil.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Sylvestre
authors.affiliation: Laboratório de Fisiologia e Controle de Artrópodes Vetores, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brazil; Instituto de Biologia do Exército, Rio de Janeiro, Brazil.
authors.forename: Simone Costa
authors.initials: SC
authors.lastname: Araújo
authors.affiliation: Laboratório de Fisiologia e Controle de Artrópodes Vetores, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brazil; Instituto de Biologia do Exército, Rio de Janeiro, Brazil.
authors.forename: José Bento Pereira
authors.initials: JB
authors.lastname: Lima
authors.affiliation: Laboratório de Fisiologia e Controle de Artrópodes Vetores, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brazil; Instituto de Biologia do Exército, Rio de Janeiro, Brazil; Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular (INCT-EM), Rio de Janeiro, Brazil.
authors.forename: Ademir Jesus
authors.initials: AJ
authors.lastname: Martins
authors.affiliation: Secretaria de Vigilância em Saúde, Ministério da Saúde, Brasília, Brazil.
authors.forename: Giovanini Evelim
authors.initials: GE
authors.lastname: Coelho
authors.affiliation: Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular (INCT-EM), Rio de Janeiro, Brazil; Laboratório de Biologia Molecular de Flavivírus, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brazil.
authors.forename: Denise
authors.initials: D
authors.lastname: Valle
mesh_terms: D000330:Aedes / Q000187:drug effects*; D000818:Animals; D001938:Brazil / Q000453:epidemiology; D003715:Dengue / Q000453:epidemiology* / Q000635:transmission; D003716:Dengue Virus / Q000145:classification; D004196:Disease Outbreaks; D005843:Geography; D006736:Horses; D006801:Humans; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D009032:Mosquito Control / Q000379:methods; D011159:Population Surveillance
chemical_list: D007306:Insecticides