Technical document for the implementation of interventions based on generic operational scenarios for Aedes aegypti control

Traditional methods to control the Aedes vector have had only a limited and temporary impact on disease prevention, either because they are not very effective or their coverage is limited. This publication provides a framework for planning and implementing Aedes aegypti surveillance, prevention, and vector control activities through risk stratification to support the development of potential operational scenarios at the local level. A comprehensive table provides a snapshot of “Entomological indicators (available methods) and main entomological indexes for A. aegypti surveillance.

Use and acceptance of long lasting insecticidal net screens for dengue prevention in Acapulco, Guerrero, Mexico

Background Dengue, recognized by the WHO as the most important mosquito-borne viral disease in the world, is a growing problem. Currently, the only effective way of preventing dengue is vector control. Standard methods have shown limited effect, and there have been calls to develop new integrated vector management approaches. One novel tool, protecting houses with long lasting insecticidal screens on doors and windows, is being trialled in a cluster randomised controlled trial by a joint UADY/WHO TDR/IDRC study in various districts of Acapulco, Mexico, with exceptionally high levels of crime and insecurity. This study investigated the community’s perspectives of long lasting insecticidal screens on doors and windows in homes and in schools, in order to ascertain their acceptability, to identify challenges to further implementation and opportunities for future improvements. Methods This was a sequential mixed-methods study. The quantitative arm contained a satisfaction survey administered to 288 houses that had received the intervention examining their perspectives of both the intervention and dengue prevention in general. The qualitative arm consisted of Focus Group Discussions (FGDs) with those who had accepted the intervention and key informant interviews with: schoolteachers to discuss the use of the screens in schools, program staff, and community members who had refused the intervention. Results Overall satisfaction and acceptance of the screens was very high, with only some operational and technical complaints relating to screen fragility and the installation process. However, the wider social context of urban violence and insecurity was a major barrier to screen acceptance. Lack of information dissemination and community collaboration were identified as project weaknesses. Conclusions The screens are widely accepted by the population, but the project implementation could be improved by reassuring the community of its legitimacy in the context of insecurity. More community engagement and better information sharing structures are needed. The screens could be a major new dengue prevention tool suitable for widespread use, if further research supports their entomological and epidemiological effectiveness and their acceptability in different social and environmental contexts. Further research is needed looking at the impact of insecurity of dengue prevention programmes

House screening with insecticide-treated netting provides sustained reductions in domestic populations of Aedes aegypti in Merida, Mexico.

There is a need for effective methods to control Aedes aegypti and prevent the transmission of dengue, chikungunya, yellow fever and Zika viruses. Insecticide treated screening (ITS) is a promising approach, particularly as it targets adult mosquitoes to reduce human-mosquito contact. A cluster-randomised controlled trial evaluated the entomological efficacy of ITS based intervention, which consisted of the installation of pyrethroid-impregnated long-lasting insecticide-treated netting material fixed as framed screens on external doors and windows. A total of 10 treatment and 10 control clusters (100 houses/cluster) were distributed throughout the city of Merida, Mexico. Cross-sectional entomological surveys quantified indoor adult mosquito infestation at baseline (pre-intervention) and throughout four post-intervention (PI) surveys spaced at 6-month intervals corresponding to dry/rainy seasons over two years (2012-2014). A total of 844 households from intervention clusters (86% coverage) were protected with ITS at the start of the trial. Significant reductions in the indoor presence and abundance of Ae. aegypti adults (OR = 0.48 and IRR = 0.45, P<0.05 respectively) and the indoor presence and abundance of Ae. aegypti female mosquitoes (OR = 0.47 and IRR = 0.44, P<0.05 respectively) were detected in intervention clusters compared to controls. This high level of protective effect was sustained for up to 24 months PI. Insecticidal activity of the ITS material declined with time, with ~70% mortality being demonstrated in susceptible mosquito cohorts up to 24 months after installation. The strong and sustained entomological impact observed in this study demonstrates the potential of house screening as a feasible, alternative approach to a sustained long-term impact on household infestations of Ae. aegypti. Larger trials quantifying the effectiveness of ITS on epidemiological endpoints are warranted and therefore recommended

Insecticide-Treated House Screens to Reduce Infestations of Dengue Vectors

The public health importance of the endophilic mosquito Aedes aegypti increased dramatically in the recent decade, because it is the vector of dengue, chikungunya, Zika and yellow fever. The use of long-lasting insecticidal nets (LLINs) fixed on doors and windows, as insecticide-treated screening (ITS), is one innovative approach recently evaluated for Aedes control in South Mexico. From 2009 to 2014, cluster-randomised controlled trials were conducted in Acapulco and Merida. Intervention clusters received Aedes-proof houses (‘Casas a prueba de Aedes’) with ITS and were followed up during 2 years. Overall, results showed significant and sustained reductions on indoor adult vector densities in the treated clusters with ITS after 2 years: ca. 50% on the presence (OR ≤ 0.62, P < 0.05) and abundance (IRR ≤ 0.58, P < 0.05). ITS on doors and windows are ‘user-friendly’ tool, with high levels of acceptance, requiring little additional work or behavioural change by householders. Factors that favoured these interventions were (a) house construction, (b) high coverage achieved due to the excellent acceptance by the community and (c) collaboration of the vector control services; and only some operational complaints relating to screen fragility and the installation process. ITS is a housing improvement that should be part of the current paradigms for urban vector-borne disease control

Efectividad de repelentes comerciales disponibles contra el mosquito Aedes aegypti (L.) en Yucatán, México

Objetivo. Determinar la eficacia de repelentes comerciales disponibles en Yucatán contra el mosquito Aedes aegypti, vector del dengue, Chikungunya y Zika. Material y métodos. Se determinó el tiempo de protección con base en el protocolo WHO/CTD/WHOPES/IC y la NOM-032- SSA2-2014. Resultados. Sólo el repelente con DEET (N, N-dietil-3-metilbenzamida) al 25% cumplió con la protección recomendada. La eficacia fue directamente proporcional a la concentración del DEET; aquéllos con componentes botánicos fueron poco o nada protectores. Conclusiones. Los resultados muestran que los repelentes con DEET proveen protección contra Ae. Aegypti; los repelentes botánicos, incluyendo las pulseras impregnadas, ofrecen nula protección. ABSTRACT Objective. We assessed the efficacy of commercial repellents available in Yucatan against Aedes aegypti, vector of dengue, Chikungunya and Zika. Materials and methods. Protection time was determined based on WHO/CTD/ WHOPES/IC y la NOM-032-SSA2-2014. Results. Products with DEET (N, N-diethyl-3-methylbenzamide) at 25% met the recommended protection. Efficacy was directly proportional to the concentration of DEET; botanicals repellents resulted no protective. Conclusions. Repellents with DEET provided more protection against Ae. aegypti and botanical repellents, including impregnated wristbands, provided no protection

Low-Cost Materials for Do-It-Yourself (DIY) Installation of House Screening against <em>Aedes aegypti</em>

House-screening (HS) using fixed-aluminium frames to reduce the risk of indoor infestation with Aedes aegypti mosquitoes as well as the risk of Aedes-transmitted diseases in communities living in endemic areas. However, the success of this approach has been hindered by the elevated cost of the aluminium-based materials as well as their professional installation, which cannot be afforded by people living under vulnerable conditions. Cost-saving strategies such as the use of low-cost materials including wood, PVC, and Velcro are within the list of HS options available and offered by HS businesses and/or Do-it-yourself (DIY) packages verbi gratia ready-made and ready-to-install mosquito-screens. Here, we evaluated the efficacy of low-cost frames constructed with different materials to protect against Ae. aegypti indoor infestation using experimental huts. The efficacy of protection in preventing female mosquito passing inside the huts of any of the options of frames was high (>93%) compared to the control with no-screen. People’s perceptions on the different materials showed the most “popular” alternative was the frame made of wood (62%). All the prototype-frames of HS made of different materials were effective at blocking Ae. aegypti entering-mosquitoes particularly, low-cost options like magnets and Velcro

Seroprevalencia de Trypanosoma cruzi en niños de Veracruz, México: línea de base epidemiológica para un modelo de control fundamentado en la transmisión activa de la enfermedad de Chagas

Introduction. In 2021 the Ministry of Health of Mexico and the Pan American Health Organization launched an initiative to interrupt intra-domiciliary vector transmission of Chagas Disease (CD), based on knowledge of the prevalence of this disease in children. The Mexican State of Veracruz was the leading of this initiative.Objective. To estimate the seroprevalence of Trypanosoma cruzi infection among children under 15 years of age from rural areas of Veracruz, Mexico.Materials and methods. Eight priority localities from the Municipality of Tempoal, Veracruz, were identified for baseline serology. Blood samples were collected on filter paperfrom 817 individuals (June-August 2017) for screening using a third-generation enzyme immunoassay. Reactive cases were confirmed by indirect hemagglutination (HAI), Enzyme linked immunosorbent assay (ELISA), and indirect immunofluorescence (IIF) tests with peripheral blood serum samples. Seroprevalence and its 95% confidence interval (95% C.I.) were calculated.. Results. In the localities Citlaltepetl, Cornizuelo, Cruz de Palma y Rancho Nuevo, CD cases were confirmed in children under 15 years of age with a seroprevalence of 1,9% (95% C.I.: 1,12-3,16%). Conclusions. These results indicate that these communities present recent transmission of CD and allow establishing an epidemiological baseline for the design and implementation of a model based on activities focused on geographic areas with active transmission to advance towards the elimination of intra-domiciliary vector transmission of CD in Mexico.Introducción. En 2021 la Secretaría de Salud de México y la Organización Panamericana de la Salud lanzaron una iniciativa para la interrupción de la transmisión vectorial intradomiciliaria de la enfermedad de Chagas (EC), fundamentada en el conocimiento de la prevalencia de esta enfermedad en población infantil. El estado mexicano de Veracruz fue punta de lanza de esta iniciativa.Objetivo. Estimar la seroprevalencia de infección por Trypanosoma cruzi en menores de 15 años de localidades rurales de Veracruz, México.Materiales y métodos. Se identificaron 8 localidades prioritarias para la serología basal en el municipio de Tempoal, Veracruz. Se colectaron muestra de sangre en papel filtro de 817 individuos (junio-agosto de 2017) para su tamizaje usando un inmunoensayo enzimático de tercera generación. Los casos reactivos del tamizaje se confirmaron mediante pruebas de hemaglutinación indirecta (HAI), ensayo por inmunoabsorción ligado a enzimas (ELISA) e inmunofluorescencia indirecta (IFI) en muestras de suero colectadas en tubo. Se calculó la seroprevalencia y su intervalo de confianza del 95% (I.C. 95%).Resultados. En las localidades Citlaltépetl, Cornizuelo, Cruz de Palma y Rancho Nuevo se confirmaron casos de la EC en menores de 15 años con una seroprevalencia de 1,9% (I.C. 95%: 1,12-3,16%).Conclusiones. Los resultados indican que estas comunidades presentan transmisión reciente de la EC y permiten establecer una línea de base epidemiológica para el diseño e implementación de un modelo fundamentado en acciones dirigidas a áreas geográficas con transmisión activa para avanzar hacia la eliminación de transmisión vectorial intradomiciliar de la EC en México

Insecticide-treated house screening protects against Zika-infected Aedes aegypti in Merida, Mexico

There is strong and unquestionable epidemiological evidence of the protective efficacy of insecticide treated screens (ITS) against an arboviral disease of major relevance. Houses with ITS were 79-85% less infested with Aedes females than control houses during the peak of the zika epidemic, an effect that was significant up to a year. A similar significant trend was observed for blood-fed Ae. aegypti females (76-82%). Communities strongly accepted the intervention, due to its perceived mode of action, the prevalent risk for Aedes-borne diseases in the area, and the positive feedback from neighbours receiving ITS. The paper provides details of the study