A new WHO bottle bioassay method to assess the susceptibility of mosquito vectors to public health insecticides: results from a WHO-coordinated multi-centre study.

BACKGROUND: The continued spread of insecticide resistance in mosquito vectors of malaria and arboviral diseases may lead to operational failure of insecticide-based interventions if resistance is not monitored and managed efficiently. This study aimed to develop and validate a new WHO glass bottle bioassay method as an alternative to the WHO standard insecticide tube test to monitor mosquito susceptibility to new public health insecticides with particular modes of action, physical properties or both. METHODS: A multi-centre study involving 21 laboratories worldwide generated data on the susceptibility of seven mosquito species (Aedes aegypti, Aedes albopictus, Anopheles gambiae sensu stricto [An. gambiae s.s.], Anopheles funestus, Anopheles stephensi, Anopheles minimus and Anopheles albimanus) to seven public health insecticides in five classes, including pyrethroids (metofluthrin, prallethrin and transfluthrin), neonicotinoids (clothianidin), pyrroles (chlorfenapyr), juvenile hormone mimics (pyriproxyfen) and butenolides (flupyradifurone), in glass bottle assays. The data were analysed using a Bayesian binomial model to determine the concentration-response curves for each insecticide-species combination and to assess the within-bioassay variability in the susceptibility endpoints, namely the concentration that kills 50% and 99% of the test population (LC50 and LC99, respectively) and the concentration that inhibits oviposition of the test population by 50% and 99% (OI50 and OI99), to measure mortality and the sterilizing effect, respectively. RESULTS: Overall, about 200,000 mosquitoes were tested with the new bottle bioassay, and LC50/LC99 or OI50/OI99 values were determined for all insecticides. Variation was seen between laboratories in estimates for some mosquito species-insecticide combinations, while other test results were consistent. The variation was generally greater with transfluthrin and flupyradifurone than with the other compounds tested, especially against Anopheles species. Overall, the mean within-bioassay variability in mortality and oviposition inhibition were < 10% for most mosquito species-insecticide combinations. CONCLUSION: Our findings, based on the largest susceptibility dataset ever produced on mosquitoes, showed that the new WHO bottle bioassay is adequate for evaluating mosquito susceptibility to new and promising public health insecticides currently deployed for vector control. The datasets presented in this study have been used recently by the WHO to establish 17 new insecticide discriminating concentrations (DCs) for either Aedes spp. or Anopheles spp. The bottle bioassay and DCs can now be widely used to monitor baseline insecticide susceptibility of wild populations of vectors of malaria and Aedes-borne diseases worldwide.

Comportamiento de picadura de Anopheles darlingi Root,1926 (Diptera: Culicidae) y su asociación con la transmisiónde malaria en Villavicencio (Colombia) / Biting behavior of Anopheles darlingi Root, 1926 (Diptera: Culicidae) and its association with malaria transmission in Villavicencio (Meta, Colombia)

Introducción. Anopheles darlingi es el principal vector de la malaria, o paludismo, en el neotrópico. Esta especie es reconocida por presentar un comportamiento antropofílico y variabilidad en sus hábitos de picadura a lo largo de su rango de distribución. Objetivo. Caracterizar el comportamiento de picadura de An. darlingi y establecer su relación con la transmisión de la malaria en Villavicencio. Materiales y métodos. Entre 2008 y 2009 se llevaron a cabo un estudio de tipo transversal y uno longitudinal, en cinco localidades de Villavicencio con transmisión de malaria. Estos incluyeron recolección de ejemplares inmaduros y de adultos en las viviendas. Se utilizó la prueba ELISA para la detección de infección con Plasmodium spp. Resultados. Se recolectaron 2.772 mosquitos. Anopheles darlingi fue la especie predominante en las capturas con atrayente humano. Los criaderos identificados para esta especie fueron pantanos, caños, lagunas y estanques piscícolas. Anopheles darlingi estuvo presente durante todo el año, con densidades mensuales promedio entre 2,2 y 55,5 mosquitos por persona por noche. Presentó actividad hematofágica durante toda la noche en el intradomicilio y en el peridomicilio. De las 18:00 a las 22:00, se registraron entre el 47 % y el 81 % de los mosquitos capturados en 12 horas de observación. Se encontró una tasa de infección con Plasmodium falciparum de 0,05 % y se estimó una tasa entomológica de inoculación de 2,9 picaduras infecciosas por persona al año. Conclusión. Anopheles darlingi se encontró infectado con P. falciparum, estuvo presente durante todo el año y exhibió características en su comportamiento de picadura que favorecen el contacto entre humano y vector, lo cual es un riesgo permanente para la transmisión de la malaria en Villavicencio.

Introduction: Anopheles darlingi is the main malaria vector in the neotropics. This species is recognized by its anthropophilic behavior and its high variability in biting activity throughout its distribution range. Objective: To characterize the biting behavior of An. darlingi and to establish its association with malaria transmission in Villavicencio. Materials and methods: Between 2008 and 2009, a cross sectional and a longitudinal entomological study were carried out in 5 localities with malaria transmission in Villavicencio. Mosquito collections included breeding sites search and human landing catches in houses. Collected mosquitoes were analyzed for Plasmodium using the ELISA standard protocol. Results: A total of 2,772 mosquitoes were collected in the study. Anopheles darlingi was the most abundant anopheline species. The most common breeding sites for this species were marshes, streams, lakes and fish ponds. Anopheles darlingi was found at all times during the year with monthly average human biting rates between 2.2 y 55.5 mosquitos/person/night. This species was collected throughout the night, indoors and outdoors, and 47 to 81% of An. darling captured during twelve hours of observation (18:00 to 06:00) were collected between18:00 and 22:00. Anopheles darlingi was found positive for P. falciparum with a 0.05% rate and the entomological inoculation rate was estimated at 2.9 infective bites/person per year. Conclusion: Anopheles darlingi was infected with P. falciparum, it was found all year long and it exhibited characteristics in biting behavior that favor human-vector contact, being a permanent risk for malaria transmission in Villavicencio.

[Biting behavior of Anopheles darlingi Root, 1926 (Diptera: Culicidae) and its association with malaria transmission in Villavicencio (Meta, Colombia)]. / Comportamiento de picadura de Anopheles darlingi Root,1926 (Diptera: Culicidae) y su asociación con la transmisiónde malaria en Villavicencio (Colombia).

INTRODUCTION: Anopheles darlingi is the main malaria vector in the neotropics. This species is recognized by its anthropophilic behavior and its high variability in biting activity throughout its distribution range. OBJECTIVE: To characterize the biting behavior of An. darlingi and to establish its association with malaria transmission in Villavicencio. MATERIALS AND METHODS: Between 2008 and 2009, a cross sectional and a longitudinal entomological study were carried out in 5 localities with malaria transmission in Villavicencio. Mosquito collections included breeding sites search and human landing catches in houses. Collected mosquitoes were analyzed for Plasmodium using the ELISA standard protocol. RESULTS: A total of 2,772 mosquitoes were collected in the study. Anopheles darlingi was the most abundant anopheline species. The most common breeding sites for this species were marshes, streams, lakes and fish ponds. Anopheles darlingi was found at all times during the year with monthly average human biting rates between 2.2 y 55.5 mosquitos/person/night. This species was collected throughout the night, indoors and outdoors, and 47 to 81% of An. darling captured during twelve hours of observation (18:00 to 06:00) were collected between18:00 and 22:00. Anopheles darlingi was found positive for P. falciparum with a 0.05% rate and the entomological inoculation rate was estimated at 2.9 infective bites/person per year. CONCLUSION: Anopheles darlingi was infected with P. falciparum, it was found all year long and it exhibited characteristics in biting behavior that favor human-vector contact, being a permanent risk for malaria transmission in Villavicencio.

Diagnóstico preliminar de la molestia sanitaria causada por Culicoides (Diptera: Ceratopogonidae) / Culicoides biting nuisance (Diptera: Ceratopogonidae) in the province of Boyacá, Colombia

Introducción. Los habitantes del occidente del departamento de Boyacá han reportado molestia sanitaria y problemas dermatológicos ocasionados por la constante picadura de insectos del género Culicoides. Objetivo. Identificar el área de Boyacá afectada por Culicoides, determinar las especies antropofílicas involucradas y su abundancia. Materiales y métodos. Se solicitó información sobre la molestia sanitaria y el registro decasos dermatológicos asociados a la picadura de Culicoides a las autoridades de salud de los municipios que por sus reportes previos o por sus características geográficas se consideraron como potencialmente afectados. En los municipios que informaron sufrir la problemática, se realizó un muestreo entomológico con atrayente humano afuera de las viviendas. Resultados. Se confirmó la gravedad de la molestia en el área rural de nueve municipios ubicados en el flanco occidental de la Cordillera Oriental. Aunque los registros epidemiológicos fueron fragmentados, se estableció que en seis municipios el 11,4 por ciento de los casos (n=2.472) dedermatitis reportados entre el 2003 y el 2005 fueron atribuidos a la picadura de Culicoides. Los resultados entomológicos mostraron que la especie dominante fue Culicoides pachymerus, 99,3 porcentaje de las 3.389 hembras recolectadas, con tasas de picadura (promedios geométricos) por municipio de hasta 52 hembras/persona en 5 minutos. Mediante análisis multivariado, se encontró que la abundancia de esta especie se relaciona negativamente con la altitud. Conclusiones. Por su dominancia y altas tasas de picadura, C. pachymerus es muy probablemente la especie responsable de la molestia sanitaria y los problemas dermatológicos causados por Culicoides en el departamento de Boyacá.

[Preliminary evaluation of the Culicoides biting nuisance (Diptera: Ceratopogonidae) in the province of Boyacá, Colombia]. / Diagnóstico preliminar de la molestia sanitaria causada por Culicoides (Diptera: Ceratopogonidae) en el departamento de Boyacá, Colombia.

INTRODUCTION: Inhabitants in the western border of Boyacá province have reported high nuisance levels and dermatologic problems caused by the intensely irritating bites of the very small flies of the genus Culicoides. OBJECTIVE: A survey was carried out to locate the affected area, identify the anthropophylic Culicoides species and estimate its abundance in Boyacá. MATERIALS AND METHODS: Nuisance reports and clinical records of dermatologic cases associated with Culicoides bites were requested from health authorities in counties where nuisance reports had been received or which had geographical features apparently favorable for Culicoides infestations. An outdoors entomological survey using human landing catches was undertaken in areas reporting a pest problem. RESULTS: Culicoides infestations were confirmed as a serious nuisance problem in the rural areas of nine counties located in the western foothills of the Eastern Range of the Colombian Andes. Although available epidemiological records were fragmented, it was established that in six counties 11.4% of the dermatitis cases (total=2,472 cases) reported between 2003 and 2005 were attributed to the Culicoides bites. The entomological survey identified Culicoides pachymerus as the dominant species, 99.3% of 3,389 caught females. Biting rates in the most intensely affected areas reach a geometric mean of 52 females/person per 5 minutes. Multivariate analysis indicated that abundance of C. pachymerus had a negative relationship with altitude. CONCLUSIONS: Based on its dominance and high biting rates, C. pachymerus is probably the species responsible for the high nuisance levels caused by Culicoides bites and the associated dermatological pathology, within the study area.