Abstract
BackgroundDuring 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.Methods/Principal FindingsVector 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.ConclusionsDespite 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.
Highlights
Dengue fever is a mosquito-borne disease caused by antigenically related but distinct virus serotypes (DENV-1, -2, -3 or -4)
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
Summary
Dengue fever is a mosquito-borne disease caused by antigenically related but distinct virus serotypes (DENV-1, -2, -3 or -4). In spite of remarkable efforts from public health authorities, organizations and research institutes, it has proven very challenging to achieve effective and sustainable control of Ae. aegypti on a long-term basis and disrupt dengue outbreaks This issue has multiple causes, including (a) uncontrolled and unplanned urbanization, providing abundant mosquito breeding sites, (b) lack of basic sanitation and regular distribution of piped water, leading to improvised storage by householders, (c) greater mobility of potentially infected hosts, increasing areas with circulation of multiple serotypes, (d) low investment in proactive vector control measures as well as in area-wide community-based approaches and (e) persistent use of vector control methods that have limited efficacy [6,7,8]. 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
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