Field Efficacy of Larvivorous Fish and Pyriproxyfen Combined with Community Engagement on Dengue Vectors in Cambodia: A Randomized Controlled Trial

Abstract

Evidence on the effectiveness of low-cost, sustainable biological vector control tools for Aedes mosquitoes is limited. Therefore, the purpose of this trial was to estimate the impact of guppy fish in combination with the larvicide pyriproxyfen (PPF) (Sumilarv® 2MR) and communication for behavioral impact (COMBI) activities to reduce entomological indices in Cambodia. In this cluster randomized, controlled superiority trial, 30 clusters comprised of one or more villages each was allocated in a 1:1:1 ratio to receive either 1) all three interventions (guppies, PPF, and COMBI), 2) two interventions (guppies and COMBI), or 3) control (standard vector control). Entomological surveys among 40 randomly selected households per cluster were carried out quarterly. The primary outcome was the population abundance of adult female Aedes mosquitoes trapped using adult resting collections. In the primary analysis, adult female Aedes abundance and mosquito infection rates was aggregated over follow-up time points to give a single rate per cluster. These data were analyzed by negative binomial regression, yielding abundance ratios (ARs). The number of Aedes females was reduced roughly by half compared with the control in both the guppy, PPF, and COMBI arm (AR = 0.54; 95% CI, 0.34–0.85; P = 0.0073); and the guppy and COMBI arm (AR = 0.49; 95% CI, 0.31–0.77; P = 0.0021). The effectiveness demonstrated and extremely low cost of including fish rearing in community-based health structures suggest they should be considered as a vector control tool as long as the benefits outweigh any potential environmental concerns. Sumilarv® 2MR was also highly accepted and preferred over current vector control tools used in Cambodia.

Entomological outcomes of cluster-randomised, community-driven dengue vector-suppression interventions in Kampong Cham province, Cambodia

“…In the February 2020 survey, guppies were found in 40.7% of eligible containers in the Intervention Arm. This compares with the earlier cluster-randomised trial in the same villages in which guppy coverage was approximately 60–70% [ 17 ] and with non-randomised studies in Cambodia in which Poecilia reticulata were found in 57% of eligible containers [ 20 ] and 88% of eligible containers [ 21 ], respectively. Guppy fish coverage may have been lower in this project than previous projects due to the passive nature of guppy fish distribution, which relied in particular on school children taking fish home to their households.…”

“…The use of the guppy fish Poecilia reticulata in household water containers was found to be highly acceptable to the households in the surveys, and guppies were present in almost 10% of containers in the August 2018 survey, before the project began to distribute the fish, showing a background use of guppy fish in Kampong Cham province which is likely related to previous studies of guppies in the same province and same villages [ 17 , 21 ]. Guppy fish appeared to be effective predators of immature mosquito stages, although they were unable to eat all the immature stages in their containers: across the four surveys, the Container Index in containers with guppies was 4.0% compared with 21.6% in containers without guppies, an 81% reduction.…”

“…In the February 2020 survey in this study, the Container Index was 89% higher in the Control Arm than the Intervention Arm. In the other cluster-randomised trial, the Container Index was 38% higher in the Control Arm than the Intervention Arm [ 17 ]. In the non-randomised study with 57% guppy coverage, it was 77% higher in the Control than the Intervention Arm [ 20 ], while in the study with 88% guppy coverage, it was approximately 90% higher in the Control than the Intervention Arm [ 21 ].…”

“…Bacillus thuringiensis israelensis ( Bti ), a facultative anaerobic Gram-positive bacterium which produces toxins that kill immature mosquito stages and is available as a water-dispersible granule, showed promise in two trials in Cambodia [ 14 , 15 ] and is being evaluated further by the Cambodian government [ 9 ]. The larvicide pyriproxyfen, sold under the trade name Sumilarv, showed promise in a 2008 field trial and proved effective in a recent cluster-randomised trial in Cambodia [ 16 , 17 ]. A further biological control strategy is the use of larvivorous guppy fish in water containers.…”

“…A cluster-randomised trial of the use of guppy fish was conducted in Kampong Cham province in Cambodia over one year from 2015–16, with results published by Hustedt et al (2021) [ 17 ]. It was a three-arm trial comparing entomological outcomes in a control arm, an intervention arm which used guppy fish in combination with Communication for Behavioural Impact (COMBI) activities, and an intervention arm which additionally used Sumilarv in combination with guppy fish and COMBI activities.…”