Laboratory wash resistance of long-lasting insecticidal nets.

Long-lasting insecticidal nets (LLINs) may eliminate the need for retreatment of mosquito nets used for the control of malaria and other vector-borne diseases. The efficacy of LLINs after repeated washing under laboratory conditions has been used to predict long-lasting efficacy under field conditions. We evaluated under laboratory conditions the wash resistance of two LLINs (PermaNet 1.0, Vestergaard-Frandsen, Denmark; Olyset, Sumitomo Chemical Co., Japan), two candidate LLINs (Dawa, Siamdutch Mosquito Netting Co., Thailand; Insector, Athanor, France) and a net treated with a process designed to increase its wash resistance and compared them with conventionally treated nets (deltamethrin, 25 mg/m(2)). Nets of all six types were washed using a standard protocol and tested weekly using WHO cone bioassays with Anopheles gambiae (Kisumu strain). The PermaNet 1.0 was the most wash resistant with >50% mosquito mortality in WHO cone bioassays after as many as 20 washes. The Dawa net also retained some activity after repeated washing but exhibited wide variation in insecticide retention and biological activity. The remaining nets lost >90% of their biological activity after six washes as measured by 24-h mortality of A. gambiae in WHO cone tests. After 20 washes, all nets lost >50% of their initial insecticide concentrations except for the Olyset net. After 20 washes, nets were heated for 4 h at 60 degrees C to determine whether biological activity could be restored by heat-assisted regeneration. Only the Olyset net was regenerated by heating, with average mosquito mortality and knockdown in WHO cone tests rising to >90% after heating for 4 h at 60 degrees C. However, regeneration of the biological activity of Olyset nets that had been washed three times did not occur at 30 degrees C or 35 degrees C after 12 weeks. The wash resistance of these LLINs corresponded well to their retention of biological activity observed in a field trial, suggesting that wash resistance may be a good predictor of the longevity of insecticidal activity of LLINs under field conditions.

High-performance liquid chromatographic assay for the simultaneous determination of sulfadoxine and pyrimethamine from whole blood dried onto filter paper.

A method using solid-phase extraction and high-performance liquid chromatography is evaluated for the simultaneous determination of sulfadoxine and pyrimethamine from 0.1 ml of whole blood dried onto filter paper. Extraction recoveries are about 60% for both drugs. The coefficient of variation for intra-assay precision, inter-assay precision and accuracy is less than 10% for sulfadoxine (10-100 microg/ml) and pyrimethamine (1-10 microg/ml).

Prevalence of malaria parasitemia and accuracy of microscopic diagnosis in Haiti, October 1995 / Prevalencia de parasitemia por malaria y precisión del diagnóstico microscópico en Haití, octubre de 1995

In October 1995 the Ministry of Public Health and Population in Haiti surveyed 42 health facilities for the prevalence and distribution of malaria infection. They examined 1.083 peripheral blood smears from patients with suspected malaria; the overall slide positivity rate was 4.0 por cent (range, 0.0 por cent to 14.3 por cent). The rate was lowest among 1-to 4-year-old children (1.6 por cent) and highest among persons aged 15 and older (5.5 por cent). Clinical and microscopic diagnoses of malaria were unreliable; the overall sensitivity of microscopic diagnosis was 83.6 por cent, specificity was 88.6 por cent, and the predictive value of a positive slide was 22.2 por cent. Microscopic diagnoses need to be improved, and adequate surveillance must be reestablished to identify areas where transmission is most intense. The generally low level of malaria is encouraging and suggests that intensified control efforts targeted to the areas of highest prevalence could furhter diminish the effect of malaria in Haiti

En octubre de 1995 el Ministerio de Salud Pública y Población de Haití inspeccionó 42 establecimientos de salud para determinar la prevalencia y distribución de la infección por malaria. Se examinaron 1 803 frotis de sangre periférica obtenidos de pacientes con sospecha de tener esa enfermedad; la tasa general de positividad de los frotis fue de 4,0% (con un recorrido de 0,0 a 14,3%). La tasa más baja (1,6%) se observó en el grupo de niños de 1 a 4 años y la más alta en personas de 15 años de edad o mayores (5,5%). Los diagnósticos clínico y microscópico de la malaria fueron poco confiables; la sensibilidad general del diagnóstico microscópico fue de 83,6% y su especificidad de 88,6%, y el valor predictivo de un frotis positivo fue de 22,2%. Es preciso mejorar los diagnósticos microscópicos y reestablecer una vigilancia adecuada a fin de identificar las zonas donde la transmisión es más intensa. La frecuencia relativamente baja de la malaria es un dato alentador y sugiere que el refuerzo de las iniciativas de control dirigidas a las zonas de mayor prevalencia podría mitigar aun más el efecto de la malaria en Haití

Prevalence of malaria parasitemia and accuracy of microscopic diagnosis in Haiti October 1995

In October 1995 the Ministry of Public Health and Population in Haiti surveyed 42 health facilities for the prevalence and distribution of malaria infection. They examined 1,803 peripheral blood smears from patients with suspected malaria; the overall slide positivity rate was 4.0 percent (range, 0.0 percent to 14.3 percent). The rate was lowest among 1-to 4-year-old children (1.6 percent) and highest among persons aged 15 and older (5.5 percent). Clinical and microscopic diagnoses of malaria were unreliable; the overall sensitivity of microscopic diagnosis was 83.6 percent, specificity was 88.6 percent, and the predictive value of a positive slide was 22.2 percent. Microscopic diagnoses need to be improved, and edequate surveillance must be reestablished to identify areas where transmission is most intense. The generally low level of malaria is encouraging and suggests that intensified control efforts (AU)

Prevalence of malaria parasitemia and accuracy of microscopic diagnosis in Haiti, October 1995

In October 1995 the Ministry of Public Health and Population in Haiti surveyed 42 health facilities for the prevalence and distribution of malaria infection. They examined 1.083 peripheral blood smears from patients with suspected malaria; the overall slide positivity rate was 4.0 por cent (range, 0.0 por cent to 14.3 por cent). The rate was lowest among 1-to 4-year-old children (1.6 por cent) and highest among persons aged 15 and older (5.5 por cent). Clinical and microscopic diagnoses of malaria were unreliable; the overall sensitivity of microscopic diagnosis was 83.6 por cent, specificity was 88.6 por cent, and the predictive value of a positive slide was 22.2 por cent. Microscopic diagnoses need to be improved, and adequate surveillance must be reestablished to identify areas where transmission is most intense. The generally low level of malaria is encouraging and suggests that intensified control efforts targeted to the areas of highest prevalence could furhter diminish the effect of malaria in Haiti

Efectos de los mosquiteros impregnados con permetrina sobre los vectores de la malaria en el norte de Guatemala / Effects of permethrin-impregnated bed nets on malaria vectors of Northern Guatemala

En un estudio con controles efectuado durante 16 meses en cuatro comunidades del norte de Guatemala, se evaluaron los efectos causados en los vectores de la malaria por mosquiteros impregnados con permetrina. Anopheles albimanus y An. vestitipennis son los vectores conocidos de la malaria en la zona. Cada casa se asignó a uno de tres grupos experimentales: las que recibieron mosquiteros impregnados con 500 mg de permetrina/m2, las que recibieron mosquiteros no tratados y aquellas en las que no se aplicaron medidas de intervención. El efecto de los mosquiteros tratados y no tratados sobre la abundancia, el comportamiento y la mortalidad de los mosquitos se determinó mediante recolecciones en el interior y el exterior de las viviendas de mosquitos que pican de noche, recoleciones matutinas con rociamientos de piretrina, inspección de la superficie de los mosquiteros para determinar la cantidad de mosquitos muertos y estudios mediante captura, liberación y recaptura. Se estimó la duración del efecto residual del insecticida en los mosquiteros tratados usando una forma modificada del ensayo biológico con conos de la OMS para empleo sobre el terreno. El contenido de piretrina en los mosquiteros se calculó mediante cromatografía de gases y líquidos. La observación más importante fue que se encontraron menos mosquitos reposando en las casas con mosquiteros tratados. Los mosquiteros tratados probablemente actuaban repeliendo y matando a los mosquitos vectores. Los estudios mediante captura, liberación y recaptura revelaron que los porcentajes de salida de las casas con mosquiteros tratados fueron más altos (94 por ciento) que los observados en las casas controles (72 por ciento), lo cual indica un efecto de repelencia. Sin embargo no se encontraron diferencias significativas entre las recolecciones de mosquitos que pican de noche en las casas con y sin mosquiteros tratados. Fue casi 20 veces más probable encontrar mosquitos anofelinos muertos en las superficies horizontales de los mosquiteros tratados que en las superficies similares de los mosquiteros no tratados. Los ennsayos biológicos indicaron que los mosquiteros impregnados con permetrina que no se lavaron retuvieron su acción onsecticida durante los 6 meses posteriores al tratamiento (AU)

Effects of Permethrin-impregnated bed nets on malaria vectors of northern Guatemala

8The authors evaluated the effects on malaria vectors of bed nets impregnated with permethrin over the course of a 16-month controlled study in four communities of Northern Guatemala. Anopheles albimanus and An. vestitipennis were the known malaria vectors in the area. Households were allocated to one of three experimental groups: those receiving bed nets impregnated with 500 mg/m2 of permethrim, those receiving untreated bed nets, and those where no intervention measures were taken. The impact of the treated and untreated bed nets on mosquito abundance, behavior, and mortality was determined by indoor/outdoor night-bite mosquito collections, morning pyrethrum spray collections, inspection of bed net surfaces for dead mosquitoes, and capture-release-recapture studies. The duration of the treated nets' residual insecticide effect was assessed by modified WHO cone fiel bioassays, and their pyrethrin content was estimated by gas-liquid chromatography analysis. The most important observation was that fewer mosquitoes were found to be resting in the households with treated bed nets. The treated nets probably functioned by both repelling and killing vector mosquitoes. Capture-release-recapture studies showed exit rated from houses with treated nets were higher (94 percent) than those from control houses (72 percent), a finding that suggests repellency. However, no significant differences were noted between the indoor night-bite mosquito collections at houses with and without treated nets. The horizontal surfaces of treated bed nets were nearly 20 times more likely to contain dead anopheline mosquitoes than were the comparable surfaces of untreated nets. The bioassays indicated that unwashed permethrin-impregnated bed nets retained their insecticidal activity for 6 months after treatment

Efectos de los mosquiteros impregnados con permetrina sobre los vectores de la malaria en el norte de Guatemala / Effects of permethrin-impregnated bed nets on malaria vectors of Northern Guatemala

En un estudio con controles efectuado durante 16 meses en cuatro comunidades del norte de Guatemala, se evaluaron los efectos causados en los vectores de la malaria por mosquiteros impregnados con permetrina. Anopheles albimanus y An. vestitipennis son los vectores conocidos de la malaria en la zona. Cada casa se asignó a uno de tres grupos experimentales: las que recibieron mosquiteros impregnados con 500 mg de permetrina/m2, las que recibieron mosquiteros no tratados y aquellas en las que no se aplicaron medidas de intervención. El efecto de los mosquiteros tratados y no tratados sobre la abundancia, el comportamiento y la mortalidad de los mosquitos se determinó mediante recolecciones en el interior y el exterior de las viviendas de mosquitos que pican de noche, recoleciones matutinas con rociamientos de piretrina, inspección de la superficie de los mosquiteros para determinar la cantidad de mosquitos muertos y estudios mediante captura, liberación y recaptura. Se estimó la duración del efecto residual del insecticida en los mosquiteros tratados usando una forma modificada del ensayo biológico con conos de la OMS para empleo sobre el terreno. El contenido de piretrina en los mosquiteros se calculó mediante cromatografía de gases y líquidos. La observación más importante fue que se encontraron menos mosquitos reposando en las casas con mosquiteros tratados. Los mosquiteros tratados probablemente actuaban repeliendo y matando a los mosquitos vectores. Los estudios mediante captura, liberación y recaptura revelaron que los porcentajes de salida de las casas con mosquiteros tratados fueron más altos (94 por ciento) que los observados en las casas controles (72 por ciento), lo cual indica un efecto de repelencia. Sin embargo no se encontraron diferencias significativas entre las recolecciones de mosquitos que pican de noche en las casas con y sin mosquiteros tratados. Fue casi 20 veces más probable encontrar mosquitos anofelinos muertos en las superficies horizontales de los mosquiteros tratados que en las superficies similares de los mosquiteros no tratados. Los ennsayos biológicos indicaron que los mosquiteros impregnados con permetrina que no se lavaron retuvieron su acción onsecticida durante los 6 meses posteriores al tratamiento (AU)

Se publica en inglés en el Bull. PAHO. Vol. 28(2), 1994

Effects of Permethrin-impregnated bed nets on malaria vectors of northern Guatemala

8The authors evaluated the effects on malaria vectors of bed nets impregnated with permethrin over the course of a 16-month controlled study in four communities of Northern Guatemala. Anopheles albimanus and An. vestitipennis were the known malaria vectors in the area. Households were allocated to one of three experimental groups: those receiving bed nets impregnated with 500 mg/m2 of permethrim, those receiving untreated bed nets, and those where no intervention measures were taken. The impact of the treated and untreated bed nets on mosquito abundance, behavior, and mortality was determined by indoor/outdoor night-bite mosquito collections, morning pyrethrum spray collections, inspection of bed net surfaces for dead mosquitoes, and capture-release-recapture studies. The duration of the treated nets' residual insecticide effect was assessed by modified WHO cone fiel bioassays, and their pyrethrin content was estimated by gas-liquid chromatography analysis. The most important observation was that fewer mosquitoes were found to be resting in the households with treated bed nets. The treated nets probably functioned by both repelling and killing vector mosquitoes. Capture-release-recapture studies showed exit rated from houses with treated nets were higher (94 percent) than those from control houses (72 percent), a finding that suggests repellency. However, no significant differences were noted between the indoor night-bite mosquito collections at houses with and without treated nets. The horizontal surfaces of treated bed nets were nearly 20 times more likely to contain dead anopheline mosquitoes than were the comparable surfaces of untreated nets. The bioassays indicated that unwashed permethrin-impregnated bed nets retained their insecticidal activity for 6 months after treatment

This article will also be published in Spanish in the BOSP. Vol. 117, 1994