Macoris MDL, Martins AJ, Andrighetti MTM, Lima JBP, Valle D. Pyrethroid resistance persists after ten years without usage against Aedes aegypti in governmental campaigns: Lessons from São Paulo State, Brazil.
PLoS Negl Trop Dis 2018;
12:e0006390. [PMID:
29601580 PMCID:
PMC5895049 DOI:
10.1371/journal.pntd.0006390]
[Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 04/11/2018] [Accepted: 03/19/2018] [Indexed: 01/12/2023] Open
Abstract
Background
Aedes aegypti, vector of dengue, chikungunya and Zika viruses, is found at high densities in tropical urban areas. The dissemination of this vector is partially the consequence of failures in current vector control methods, still mainly relying upon insecticides. In the State of São Paulo (SP), Brazil, public health managers employed pyrethroids against Ae. aegypti adults from 1989 to 2000, when a robust insecticide resistance monitoring system detected resistance to pyrethroids in several Ae. aegypti populations. However, pyrethroids are also the preferred compounds engaged in household applications due to their rapid knockdown effect, lower toxicity to mammals and less irritating smell.
Methodology/Principal findings
We evaluated pyrethroid resistance in Ae. aegypti populations over the course of a decade, from 2004 to 2015, after interruption of pyrethroid public applications in SP. Qualitative bioassays with papers impregnated with a deltamethrin diagnostic dose (DD) performed with insects from seven SP municipalities and evaluated yearly from 2006 to 2014, detected resistance in most of the cases. Quantitative bioassays were also carried out with four populations in 2011, suggesting a positive correlation between resistance level and survivorship in the DD bioassays. Biochemical tests conducted with seven insect populations in 2006 and 2015, detected increasing metabolic alterations of all major classes of detoxifying enzymes, mostly of mixed function oxidases. Genotyping of the voltage-gated sodium channel (AaNaV, the pyrethroid target-site) with a TaqMan real time PCR based technique was performed from 2004 to 2014 in all seven localities. The two kdr mutations, Val1016Ile and Phe1534Cys, known to be spread throughout Brazil, were always present with a severe decrease of the susceptible allele over time.
Conclusions/Significance
These results are discussed in the context of public and domestic insecticide use, the necessity of implementation of a strong integrated vector control strategy and the conceptual misunderstanding between 'vector control' and 'chemical control of vectors'.
Insecticides will continue to exert an essential role in the reduction of vector density and personal protection for a long time, especially during epidemics. In Brazil, these chemicals are extensively incorporated in national campaigns against Ae. aegypti, favoring the rise and dispersion of resistant populations. The State of São Paulo (SP), the capital (also named São Paulo) being the 5th most populated city in the world, interrupted pyrethroid application in 2000 given the high resistance levels registered. Nevertheless, SP Ae. aegypti populations remain resistant to pyrethroids with an ever increasing frequency of kdr mutations, one of the main mechanisms responsible for resistance to these chemicals. Although no longer employed by public authorities, pyrethroids are readily available on the commercial market and are extensively used by households as well as private companies, which may partially account for the high resistance ratios still in effect. All in all, it is essential to invest in basic infrastructural sanitation and community educational methods to consciously avoid larval breading sites as well as encourage the correct use of insecticides. Without this, we are fated to forfeit the efficacy of all insecticide classes as well as undermine any other new methods of Aedes control.
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