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A low technology emanator treated with the volatile pyrethroid transfluthrin confers long term protection against outdoor biting vectors of lymphatic filariasis, arboviruses and malaria

View Article: PubMed Central - PubMed

ABSTRACT

Background: The vapor phase of the volatile pyrethroid transfluthrin incapacitates mosquitoes and prevents them from feeding. Although existing emanator products for delivering volatile pyrethroids protect against outdoor mosquito bites, they are too short-lived to be practical or affordable for routine use in low-income settings. New transfluthrin emanators, comprised simply of treated hessian fabric strips, have recently proven highly protective against outdoor-biting vectors of lymphatic filariasis, arboviruses and malaria, but their full protective lifespan, minimum dose requirements, and range of protection have not previously been assessed.

Methodology: The effects of transfluthrin-treated hessian strips upon mosquito biting exposure of users and nearby non-users, as well as dependence of protection upon treatment dose, were measured outdoors in rural Tanzania using human landing catches (HLC).

Principal findings: Strips treated with 10ml of transfluthrin prevented at least three quarters (p < 0.001) of outdoor bites by Anopheles arabiensis, Culex spp. and Mansonia spp. mosquitoes, and >90% protection against bites on warmer nights with higher evaporation rates, for at least one year. Strips treated with this high dose also reduced biting exposure of non-users at a distance of up to 5m from the strips for An. arabiensis (p < 0.001) and up to 2m for Mansonia spp. (p = 0.008), but provided no protection to non-users against Culex spp. No evidence of increased risk for non-users, caused by diversion of mosquitoes to unprotected individuals, was found at any distance within an 80m radius. A dose of only 1ml provided equivalent protection to the 10ml dose against An. arabiensis, Culex spp. and Mansonia spp. mosquitoes over 6 months (p < 0.001).

Conclusions/significance: Transfluthrin-treated hessian emanators provide safe, affordable, long-term protection against several different pathogen-transmitting mosquito taxa that attack humans outdoors, where they are usually active and cannot be protected by bed nets or residual sprays with conventional, solid-phase insecticides.

No MeSH data available.


Related in: MedlinePlus

Schematic illustration of the design of experiments 1 and 2.Schematic (A) and photographic (B) illustration of the arrangement of human landing catches (HLC) by users of treated or untreated sacking strips and non-users sitting in exposure free M traps at specific randomized distances and angles at which a human baited trap was placed. The HLC captures conducted by the users of treated and untreated strips were used to quantify personal protection provided by the treated strips (Fig 1, Objective 1.1). Captures with nearby M traps occupied by participants lacking any treated or untreated strip were used to quantify the degree to which proximity to a protected strip user might decrease (Fig 1, Objective 1.2) or increase (Fig 1, Objective 1.3) biting exposure, over a range of distances varying from 2 to 40 meters. The same phenomenon was assessed at a distance of 80 meters by comparing the number of mosquitoes caught by users of untreated strips on nights when the other user at the other catching station in the same site used a treated strip with the numbers caught when the nearby strip user had an untreated strip.
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pntd.0005455.g002: Schematic illustration of the design of experiments 1 and 2.Schematic (A) and photographic (B) illustration of the arrangement of human landing catches (HLC) by users of treated or untreated sacking strips and non-users sitting in exposure free M traps at specific randomized distances and angles at which a human baited trap was placed. The HLC captures conducted by the users of treated and untreated strips were used to quantify personal protection provided by the treated strips (Fig 1, Objective 1.1). Captures with nearby M traps occupied by participants lacking any treated or untreated strip were used to quantify the degree to which proximity to a protected strip user might decrease (Fig 1, Objective 1.2) or increase (Fig 1, Objective 1.3) biting exposure, over a range of distances varying from 2 to 40 meters. The same phenomenon was assessed at a distance of 80 meters by comparing the number of mosquitoes caught by users of untreated strips on nights when the other user at the other catching station in the same site used a treated strip with the numbers caught when the nearby strip user had an untreated strip.

Mentions: In the first phase, (Fig 1) five strips treated with 10ml of technical grade transfluthrin (first emulsified by mixing with 90 ml of water and 10ml of liquid detergent as described above) and five untreated control strips were simultaneously assessed by rotation through four separate open-field sites (Fig 2A) within the village of Lupiro (8.385°S and 36.670°E). In this first phase, treated and untreated strips were moved in pairs between field sites and the semi-field tunnel every 3 consecutive experimental nights (See below for details of the three-night randomization cycle for strip treatments) following a 5×5 Latin square design, spanning 15 nights of experimentation for each round of experimental replication. In order to allow volunteers and supervisors four nights per working week to sleep normally, each 3-night cycle of treatment randomizations was allocated to a single working week, so each full round of experimentation was distributed across 5 working weeks. Overall, 5 rounds of experimental replication were completed over the course of phase 1, comprising over 75 nights of experimentation, 600 person-nights of outdoor human landing catches (HLC) measurements, and the same number of person-nights of outdoor mosquito catches measured by human-baited M-trap. The M-trap consisted of netting material wrapped around a wooden frame. The M-trap has two compartments, one occupied by a seated male volunteer protected by a netting panel door and another with an entry slit into which mosquitoes can fly, so that they are captured without being able to make contact with the human occupant.


A low technology emanator treated with the volatile pyrethroid transfluthrin confers long term protection against outdoor biting vectors of lymphatic filariasis, arboviruses and malaria
Schematic illustration of the design of experiments 1 and 2.Schematic (A) and photographic (B) illustration of the arrangement of human landing catches (HLC) by users of treated or untreated sacking strips and non-users sitting in exposure free M traps at specific randomized distances and angles at which a human baited trap was placed. The HLC captures conducted by the users of treated and untreated strips were used to quantify personal protection provided by the treated strips (Fig 1, Objective 1.1). Captures with nearby M traps occupied by participants lacking any treated or untreated strip were used to quantify the degree to which proximity to a protected strip user might decrease (Fig 1, Objective 1.2) or increase (Fig 1, Objective 1.3) biting exposure, over a range of distances varying from 2 to 40 meters. The same phenomenon was assessed at a distance of 80 meters by comparing the number of mosquitoes caught by users of untreated strips on nights when the other user at the other catching station in the same site used a treated strip with the numbers caught when the nearby strip user had an untreated strip.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384659&req=5

pntd.0005455.g002: Schematic illustration of the design of experiments 1 and 2.Schematic (A) and photographic (B) illustration of the arrangement of human landing catches (HLC) by users of treated or untreated sacking strips and non-users sitting in exposure free M traps at specific randomized distances and angles at which a human baited trap was placed. The HLC captures conducted by the users of treated and untreated strips were used to quantify personal protection provided by the treated strips (Fig 1, Objective 1.1). Captures with nearby M traps occupied by participants lacking any treated or untreated strip were used to quantify the degree to which proximity to a protected strip user might decrease (Fig 1, Objective 1.2) or increase (Fig 1, Objective 1.3) biting exposure, over a range of distances varying from 2 to 40 meters. The same phenomenon was assessed at a distance of 80 meters by comparing the number of mosquitoes caught by users of untreated strips on nights when the other user at the other catching station in the same site used a treated strip with the numbers caught when the nearby strip user had an untreated strip.
Mentions: In the first phase, (Fig 1) five strips treated with 10ml of technical grade transfluthrin (first emulsified by mixing with 90 ml of water and 10ml of liquid detergent as described above) and five untreated control strips were simultaneously assessed by rotation through four separate open-field sites (Fig 2A) within the village of Lupiro (8.385°S and 36.670°E). In this first phase, treated and untreated strips were moved in pairs between field sites and the semi-field tunnel every 3 consecutive experimental nights (See below for details of the three-night randomization cycle for strip treatments) following a 5×5 Latin square design, spanning 15 nights of experimentation for each round of experimental replication. In order to allow volunteers and supervisors four nights per working week to sleep normally, each 3-night cycle of treatment randomizations was allocated to a single working week, so each full round of experimentation was distributed across 5 working weeks. Overall, 5 rounds of experimental replication were completed over the course of phase 1, comprising over 75 nights of experimentation, 600 person-nights of outdoor human landing catches (HLC) measurements, and the same number of person-nights of outdoor mosquito catches measured by human-baited M-trap. The M-trap consisted of netting material wrapped around a wooden frame. The M-trap has two compartments, one occupied by a seated male volunteer protected by a netting panel door and another with an entry slit into which mosquitoes can fly, so that they are captured without being able to make contact with the human occupant.

View Article: PubMed Central - PubMed

ABSTRACT

Background: The vapor phase of the volatile pyrethroid transfluthrin incapacitates mosquitoes and prevents them from feeding. Although existing emanator products for delivering volatile pyrethroids protect against outdoor mosquito bites, they are too short-lived to be practical or affordable for routine use in low-income settings. New transfluthrin emanators, comprised simply of treated hessian fabric strips, have recently proven highly protective against outdoor-biting vectors of lymphatic filariasis, arboviruses and malaria, but their full protective lifespan, minimum dose requirements, and range of protection have not previously been assessed.

Methodology: The effects of transfluthrin-treated hessian strips upon mosquito biting exposure of users and nearby non-users, as well as dependence of protection upon treatment dose, were measured outdoors in rural Tanzania using human landing catches (HLC).

Principal findings: Strips treated with 10ml of transfluthrin prevented at least three quarters (p < 0.001) of outdoor bites by Anopheles arabiensis, Culex spp. and Mansonia spp. mosquitoes, and >90% protection against bites on warmer nights with higher evaporation rates, for at least one year. Strips treated with this high dose also reduced biting exposure of non-users at a distance of up to 5m from the strips for An. arabiensis (p < 0.001) and up to 2m for Mansonia spp. (p = 0.008), but provided no protection to non-users against Culex spp. No evidence of increased risk for non-users, caused by diversion of mosquitoes to unprotected individuals, was found at any distance within an 80m radius. A dose of only 1ml provided equivalent protection to the 10ml dose against An. arabiensis, Culex spp. and Mansonia spp. mosquitoes over 6 months (p < 0.001).

Conclusions/significance: Transfluthrin-treated hessian emanators provide safe, affordable, long-term protection against several different pathogen-transmitting mosquito taxa that attack humans outdoors, where they are usually active and cannot be protected by bed nets or residual sprays with conventional, solid-phase insecticides.

No MeSH data available.


Related in: MedlinePlus