Does washing insecticide-treated nets 20 times for experimental hut evaluations provide a suitable proxy for their end-of-life performance under household conditions?
Thomas Syme, Abel Agbevo, Josias Fagbohoun, Boris N'dombidjé, Judicael Nounagnon, Juniace Ahoga, Joël Akpi, Corine Ngufor
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引用次数: 0
Abstract
Background: Insecticide-treated nets (ITNs) are washed 20 times as part of experimental hut trials to simulate the loss of active ingredient (AI) occurring over their intended 3-year lifespan and estimate insecticidal durability. The ability of the 20-wash method to predict the end-of-life performance of ITNs has not been empirically validated.
Methods: We performed an experimental hut trial to compare the efficacy of new ITNs unwashed and washed 20 times to field-aged ITNs withdrawn from households 3 years post-distribution against a pyrethroid-resistant vector population in Covè, Benin. Four products from pyrethroid-only (Interceptor®), pyrethroid-piperonyl butoxide (PermaNet® 3.0), pyrethroid-pyriproxyfen (Royal Guard®) and pyrethroid-chlorfenapyr (Interceptor® G2) ITN types were tested. Net pieces were tested in bioassays and sent for chemical analysis to assess differences in surface AI bioavailability and total chemical content between washed and field-aged nets. Susceptibility bioassays were also performed to assess insecticide resistance in the Covè vector population.
Results: Mosquito mortality in experimental huts was similar or slightly higher with field-aged nets than washed nets with Interceptor® (11% vs. 10%, p = 0.339, OR = 1.19, 95% CIs [0.84, 1.69]), PermaNet® 3.0 (12% vs. 18%, p < 0.001, OR = 1.78, 95% CIs [1.34, 2.38]) and Royal Guard® (9% vs. 14%, p = 0.076, OR = 1.33, 95% CIs: [0.97, 1.83]). Likewise, field-aged Royal Guard® induced a similar reduction in fertility to washed Royal Guard® (22% vs. 29%, p = 0.066). In contrast, mortality was significantly lower with field-aged nets Interceptor® G2 compared to washed nets (54% vs. 19%, p < 0.001, OR = 0.18, 95% CIs [0.14, 0.24]). Blood-feeding inhibition was higher with field-aged nets than washed nets across all ITN types. Retention of non-pyrethroid AIs was lower than for the pyrethroid, particularly with field-aged nets (PermaNet® 3.0 (roof): 25% vs. 68%, p < 0.001, Royal Guard®: 27% vs. 53%, p < 0.001, Interceptor® G2: 14% vs. 39%, p < 0.001).
Conclusions: In this setting, the 20-wash method provided a suitable proxy for the end-of-life killing and sterilising performance of Interceptor®, PermaNet® 3.0 and Royal Guard® in experimental huts. In contrast, washing overestimated the end-of-life performance of Interceptor® G2 for mortality and underestimated the personal protection of all field-aged ITNs.
期刊介绍：
Parasites & Vectors is an open access, peer-reviewed online journal dealing with the biology of parasites, parasitic diseases, intermediate hosts, vectors and vector-borne pathogens. Manuscripts published in this journal will be available to all worldwide, with no barriers to access, immediately following acceptance. However, authors retain the copyright of their material and may use it, or distribute it, as they wish.
Manuscripts on all aspects of the basic and applied biology of parasites, intermediate hosts, vectors and vector-borne pathogens will be considered. In addition to the traditional and well-established areas of science in these fields, we also aim to provide a vehicle for publication of the rapidly developing resources and technology in parasite, intermediate host and vector genomics and their impacts on biological research. We are able to publish large datasets and extensive results, frequently associated with genomic and post-genomic technologies, which are not readily accommodated in traditional journals. Manuscripts addressing broader issues, for example economics, social sciences and global climate change in relation to parasites, vectors and disease control, are also welcomed.
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