Quantifying Seasonal Variation in Insecticide-Treated Net Use among Those with Access

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Background: Effective targeting and evaluation of interventions that protect against adult malaria vectors requires an understanding of how gaps in personal protection arise. An improved understanding of human and mosquito behaviour, and how they overlap in time and space, is critical to estimating the impact of insecticide-treated nets (ITNs) and determining when and where supplemental personal protection tools are needed. Methods for weighting estimates of human exposure to biting Anopheles mosquitoes according to where people spend their time were first developed over half a century ago. However, crude indoor and outdoor biting rates are still commonly interpreted as indicative of human-vector contact patterns without any adjustment for human behaviour or the personal protection effects of ITNs. Main text: A small number of human behavioural variables capturing the distribution of human populations indoors and outdoors, whether they are awake or asleep, and if and when they use an ITN over the course of the night, can enable a more accurate representation of human biting exposure patterns. However, to date no clear guidance is available on what data should be collected, what indicators should be reported, or how they should be calculated. This article presents an integrated perspective on relevant indicators of human-vector interactions, the critical entomological and human behavioural data elements required to quantify human-vector interactions, and recommendations for collecting and analysing such data. Conclusions: If collected and used consistently, this information can contribute to an improved understanding of how malaria transmission persists in the context of current intervention tools, how exposure patterns may change as new vector control tools are introduced, and the potential impact and limitations of these tools. This article is intended to consolidate understanding around work on this topic to date and provide a consistent framework for building upon it. Additional work is needed to address remaining questions, including further development and validation of methods for entomological and human behavioural data collection and analysis.

Section: Discussionmentioning

confidence: 99%

Methods and indicators for measuring patterns of human exposure to malaria vectors

Monroe

Moore

Okumu

et al. 2020

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“…Only LLINs that are being used can contribute to malaria transmission control, and LLINs that are present in households but are stored away and remain in good condition are useless until used. LLIN use, in addition to depending on presence, physical and chemical status of LLINs, depends on a plethora of factors including product quality, geographically specific use practices, knowledge about their benefits, and seasonally varying factors such as mosquito nuisance levels, temperature and humidity which impact the comfort level inside a LLIN [ 25 – 29 ]. Also, LLINs may be temporarily unavailable due to washing or travel.…”

Section: Discussionmentioning

confidence: 99%

Attrition, physical integrity and insecticidal activity of long-lasting insecticidal nets in sub-Saharan Africa and modelling of their impact on vectorial capacity

Briët

Koenker

Norris

et al. 2020

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Background: Long-lasting insecticidal nets (LLINs) are the primary malaria prevention and control intervention in many parts of sub-Saharan Africa. While LLINs are expected to last at least 3 years under normal use conditions, they can lose effectiveness because they fall out of use, are discarded, repurposed, physically damaged, or lose insecticidal activity. The contributions of these different interrelated factors to durability of nets and their protection against malaria have been unclear. Methods: Starting in 2009, LLIN durability studies were conducted in seven countries in Africa over 5 years. WHOrecommended measures of attrition, LLIN use, insecticidal activity, and physical integrity were recorded for eight different net brands. These data were combined with analyses of experimental hut data on feeding inhibition and killing effects of LLINs on both susceptible and pyrethroid resistant malaria vectors to estimate the protection against malaria transmission-in terms of vectorial capacity (VC)-provided by each net cohort over time. Impact on VC was then compared in hypothetical scenarios where one durability outcome measure was set at the best possible level while keeping the others at the observed levels. Results: There was more variability in decay of protection over time by country than by net brand for three measures of durability (ratios of variance components 4.6, 4.4, and 1.8 times for LLIN survival, use, and integrity, respectively). In some countries, LLIN attrition was slow, but use declined rapidly. Non-use of LLINs generally had more effect on LLIN impact on VC than did attrition, hole formation, or insecticide loss. Conclusions: There is much more variation in LLIN durability among countries than among net brands. Low levels of use may have a larger impact on effectiveness than does variation in attrition or LLIN degradation. The estimated

“…Unfortunately, all surveys in this study were done in the rainy season so that dry season use could not be observed. But there is good evidence from other sources to suggest that in this dry savannah area with a short and heavy rain period and a long dry period LLIN use is seasonal [25,26]. Therefore, the question arises whether a lower use rate of the cohort nets in the dry season could have contributed to the significantly better physical durability of the monitored LLIN in Zamfara.…”

Section: Discussionmentioning

confidence: 99%

Monitoring the physical and insecticidal durability of the long-lasting insecticidal net DawaPlus® 2.0 in three States in Nigeria

Obi¹,

Okoh

Blaufuss

et al. 2020

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Background: Following guidance from the US President's Malaria Initiative, durability monitoring of DawaPlus ® 2.0 brand of long-lasting insecticidal net (LLIN) distributed during the 2015/16 mass campaign was set up in three ecologically different states: Zamfara, Ebonyi and Oyo. Methods: This was a prospective cohort study of representative samples of households from each location, recruited at baseline, 1 to 6 months after the mass campaign. All campaign nets in the households were labelled and followed up over a period of 36 months in Zamfara and Ebonyi and 24 months in Oyo. Primary outcome was the "proportion of nets surviving in serviceable condition" based on attrition and integrity measures and the median survival in years. The outcome for insecticidal durability was determined by bio-assay from sub-samples of campaign nets. Results: A total of 439 households (98% of target) and 1096 campaign nets (106%) were included in the study. Definite outcomes could be determined for 92% of the cohort nets in Zamfara, 88% in Ebonyi and 75% in Oyo. All-cause attrition was highest in Oyo with 47% no longer present after 24 months, 53% in Ebonyi and 28% in Zamfara after 36 months. Overall only 1% of all campaign nets were used for other purposes. Estimated survival in serviceable condition of the campaign nets was 80% in Zamfara, 55% in Ebonyi (36 months follow-up) and 75% in Oyo (24 months follow-up) corresponding to median survival of 5.3, 3.3, 3.2 years, respectively. Factors associated with better survival were exposure to social messaging combined with a positive net-care attitude and only adult users. Failing to fold the net when hanging and having children under 5 years of age in the household negatively impacted net survival. Insecticidal effectiveness testing at final survey showed knock-down rates of 50-69%, but 24-h mortality above 95% resulting in 100% optimal performance in Ebonyi and Oyo and 97% in Zamfara. Conclusions: Results confirm the strong influence of net-use environment and behavioural factors in the physical survival of the same LLIN brand, which can increase the time until 50% of nets are no longer serviceable by up to 2 years.