Deltamethrin‐impregnated bednets reduce human landing rates of sandfly vector Lutzomyia longipalpis in Amazon households

Abstract

The entomological efficacy of using 25% deltamethrin EC insecticide-treated bednets (ITNs) was evaluated against the sandfly Lutzomyia longipalpis Lutz and Neiva (Diptera: Psychodidae), the principal vector of zoonotic visceral leishmaniasis (ZVL) in Latin America. A crossover field study in Amazon Brazil (Marajó Island, Pará State) demonstrated that, compared with untreated nets, the insecticide increased the barrier effect of nets by 39% (95% confidence interval [CI] 34-44%), reduced human landing rates by 80% (95% CI 62-90%) and increased the 24-h mortality rate from 0% to 98% (95% CI 93-99%) inside ITNs. The presence of an ITN also reduced the human landing rate on unprotected persons outside the net in the same room by 56% (95% CI 52-59%), and increased 24-h mortality to 68% (95% CI 62-73%) compared to 0.4% (0.1-2.0%) in untreated houses. The reduction in human landing rates in ITN rooms was associated with a doubling in the proportion of sandflies alighting on walls compared with that in untreated rooms, which was attributed to insecticide-induced excito-repellency. There was no evidence that sandflies were diverted onto unprotected hosts. Human landing catches inside houses peaked between 19.00 hours and 23.00 hours and declined steadily to zero at 02.00 hours and thereafter. House-to-house questionnaires established that only 34% of households owned at least one net (median two, range 1-8), only 20% of the population slept under a net (33% of 0-5-year-old children), and the majority (73%) of the population slept in hammocks. Combined data pertaining to sleeping times for children and sandfly activity period indicate that > 50% of sandfly bites inside houses, and substantially more outside houses, were taken before a third of children were potentially protected by a net. This study demonstrates the clear entomological efficacy of ITNs against Lu. longipalpis in this endemic region. The effectiveness of ITNs at preventing ZVL infection and disease has still to be evaluated.

Transmission, reservoir hosts and control of zoonotic visceral leishmaniasis

“…Possible reasons for a low efficacy of residual insecticide spraying in Brazil include low coverage, for example only spraying houses within 200 m of a human case, the relatively short-lived residual activity of pyrethroids compared to DDT (Oliveira and Melo, 1994), the higher densities of vectors outside houses (e.g. in animal sheds) and vector behaviour, as L. longipalpis is active in the early evening while people are outside houses (Quinnell and Dye, 1994 ;Courtenay et al 2007). …”

Progress in the Mathematical Modelling of Visceral Leishmaniasis

“…IRS is not expected to impact on exophilic and exophagic vectors, nor immature stages; though sandfly breeding sites are largely unknown (Alexander and Maroli, 2003). Measurable entomological indicators of control success include reductions in human landing rates, blood-feeding success, or human blood index, and reduced vector survival (lower parous rates), as demonstrated for a wide range of New World (Davies et al, 2000;Feliciangeli et al, 2003a,b;Courtenay et al, 2007;Falcao et al, 1991), and Old World sandfly species (Benzerroung et al, 1992;Reyburn et al, 2000;Joshi and Rai, 1994;Kaul et al, 1994;Mukhopadhyay et al, 1996;Joshi et al, 2009). Insecticide deterrency (sometimes called repellency cf.…”

Epidemiological situation of leishmaniasis and perception of key actors in the department of Alto Paraná, Paraguay

“…En síntesis, a pesar de la poca existencia de registros oficiales en la zona sobre la LV se requiere la implementación de medidas inmediatas para evitar su expansión, tales como la educación ambiental, el monitoreo de vectores emergentes para el control químico, el abordaje de perros polisintomáticos con las asociaciones veterinarias y la búsqueda de nuevos focos en las áreas rurales y urbanas, mediante acciones que deberán basarse en las condiciones epidemiológicas locales para ser eficaces (22,24).…”