Doum, D. | bioRxiv Science

bioRxiv2024

Field evaluation of a volatile pyrethroid spatial repellent and etofenprox-treated clothing for outdoor protection against forest malaria vectors in Cambodia

Cambodias goal to eliminate malaria by 2025 is challenged by persisting transmission in the countrys forest and forest fringe areas. People living in, or traveling to the forest, are exposed to malaria vector bites during the day due to Anopheles daytime biting; and during the night, due to low bed net use and open sleeping structures. Volatile pyrethroid spatial repellents (VPSRs), and insecticide treated clothing (ITC) may help address these gaps in protection. In this field study the authors evaluated the outdoor application of one passive, transfluthrin-based VPSR, four etofenprox-ITCs paired with a picaridin topical repellent, and a combination of VPSR and ITC against wild Anopheles landing in Cambodia. Mathematical modeling was also used to predict the reduction of vectorial capacity of these interventions. A 7x7 Latin-square (6 interventions and one control) was conducted over 49 collection nights in seven temporary, open structures in a forest in Mondulkiri Province, Cambodia. Pairs of participants conducted human landing catches (HLCs) from 18h00 to 06h00, with each collector conducting collections for six hours. A randomly selected subset of collected Anopheles were identified to species using molecular methods. The rate ratio of each intervention compared to the control on Anopheles landings was estimated using a mixed-effect negative binomial regression with intervention, structure, and collector-pair as fixed-effects, and with collection date and structure-night as random effects. The modeling assessment aims to predict the relative reduction in vectoral capacity. Initial calculations involved establishing a "baseline scenario" without intervention, utilizing biometric parameters for Anopheles dirus. Various scenarios accounting for intervention coverage and adherence were then considered. The study aims to update parameters using field study estimates for wild Anopheles, incorporating multiple semi-field estimates for interventions and accounting for the variability and uncertainty in parameter values. Of the total 8,294 Anopheles specimens collected, 15% (n=1,242) of specimens were confirmed to species or species group via PCR. Fifteen species were confirmed; Anopheles dirus Form A was predominant (n=429), followed by Anopheles maculatus (n=189), and Anopheles minimus (n=60). All six interventions reduced Anopheles landing substantially; protective efficacies ranged between 61% (95% confidence interval (CI): 48 - 71%) (etofenprox-ITC, washed) and 95% (95% CI: 93 - 96%) (combined VPSR and unwashed etofenprox-ITC). Finally, the modelling assessment demonstrates significant reductions in vectoral capacity, with the highest impact observed for the combined ITC and VPSR as well as the VPSR used alone, although effectiveness decreases with intervention aging, and variability exists in the magnitude of predicted reductions due to differences in experimental conditions. These transfluthrin-based VPSR and etofenprox ITC interventions have the potential to reduce outdoor and daytime Anopheles biting by providing substantial protection against Anopheles landing. One or more of these tools may play a valuable role in the push for elimination in Cambodia and the Greater Mekong Subregion if programs can achieve effective coverage.

ecology↗

bioRxiv2020

Field efficacy of guppies and pyriproxyfen (Sumilarv(R) 2MR) combined with community engagement on dengue vectors in Cambodia: a randomized controlled trial

Evidence on the effectiveness of low-cost, sustainable biological vector control tools for Aedes mosquitoes is limited. Therefore, the purpose of this trial is to estimate the impact of guppy fish, in combination with the use of the larvicide Pyriproxyfen (Sumilarv(R) 2MR), and Communication for Behavioral Impact (COMBI) activities to reduce entomological indices in Cambodia. In this cluster randomized, controlled superiority trial, 30 clusters comprising of one or more villages each (with approximately 170 households) will be allocated, in a 1:1:1 ratio, to receive either a) three interventions (guppies, Sumilarv(R) 2MR, and COMBI activities), b) two interventions (guppies and COMBI activities), or c) control (standard vector control). Households were invited to participate, and entomology surveys among 40 randomly selected households per cluster were carried out quarterly. The primary outcome was the population density of adult female Aedes mosquitoes (i.e. number per house) trapped using adult resting collections. Secondary outcome measures include the House index, Container index, Breteau index, Pupae Per House, Pupae Per Person, mosquito infection rate, guppy fish coverage, Sumilarv(R) 2MR coverage, and percentage of respondents with knowledge about Aedes mosquitoes causing dengue. In the primary analysis, adult female Aedes density and mosquito infection rates was aggregated over follow-up time points to give a single rate per cluster. This was analyzed by negative binomial regression, yielding density ratios. The number of Aedes females was reduced by roughly half compared to the control in both the guppy and PPF arm (Density Ratio (DR)=0.54 [95% CI 0.34-0.85], p=0.0073), and guppy arm (DR=0.49 [95% CI 0.31-0.77], p=0.0021). The extremely low cost of including guppy rearing in community-based health structures along with the effectiveness demonstrated suggest guppies should be considered as a vector control tool as long as the benefits outweigh any potential environmental concerns. PPF was also highly accepted and preferred over current vector control tools used in Cambodia, however product costs and availability are still unknown. Author SummaryDengue is one of the most rapidly spreading mosquito-borne viral diseases in the world, is caused by bites of infected Aedes mosquitoes, and can sometimes lead to death. Cambodia has one of the highest per-capita incidence rates in Asia. Without a cure or routinely available efficacious vaccine, dengue control relies largely on reduction and avoidance of mosquitoes. In Cambodia, dengue mosquito control activities are focused on larviciding with temephos and pyrethroid based adulticide sprays to which Aedes have been shown to be increasingly resistant. This study was designed to evaluate novel biological vector control tools (guppy fish and a controlled release larvicidal matrix) utilizing an integrated vector management approach with community-based methods tailored to the local context. The results indicate that the tools resulted in a statistically significant reduction in immature and adult Aedes mosquito density. The interventions were accepted by and communities were willing to pay for them. The results suggest guppies are an ideal vector control tool as long as the benefits outweigh any potential environmental concerns. PPF was also highly accepted and preferred over current vector control tools used in Cambodia, however product costs and availability are still unknown.

ecology↗