Risk Of Dengue Transmission Research Articles

The fuzzy system ensembles entomological, epidemiological, demographic and environmental data to unravel the dengue transmission risk in an endemic city

BackgroundThe effectiveness of dengue control interventions depends on an effective integrated surveillance system that involves analysis of multiple variables associated with the natural history and transmission dynamics of this arbovirus. Entomological indicators associated with other biotic and abiotic parameters can assertively characterize the spatiotemporal trends related to dengue transmission risk. However, the unpredictability of the non-linear nature of the data, as well as the uncertainty and subjectivity inherent in biological data are often neglected in conventional models.MethodsAs an alternative for analyzing dengue-related data, we devised a fuzzy-logic approach to test ensembles of these indicators across categories, which align with the concept of degrees of truth to characterize the success of dengue transmission by Aedes aegypti mosquitoes in an endemic city in Brazil. We used locally gathered entomological, demographic, environmental and epidemiological data as input sources using freely available data on digital platforms. The outcome variable, risk of transmission, was aggregated into three categories: low, medium, and high. Spatial data was georeferenced and the defuzzified values were interpolated to create a map, translating our findings to local public health managers and decision-makers to direct further vector control interventions.ResultsThe classification of low, medium, and high transmission risk areas followed a seasonal trend expected for dengue occurrence in the region. The fuzzy approach captured the 2020 outbreak, when only 14.06% of the areas were classified as low risk. The classification of transmission risk based on the fuzzy system revealed effective in predicting an increase in dengue transmission, since more than 75% of high-risk areas had an increase in dengue incidence within the following 15 days.ConclusionsOur study demonstrated the ability of fuzzy logic to characterize the city’s spatiotemporal heterogeneity in relation to areas at high risk of dengue transmission, suggesting it can be considered as part of an integrated surveillance system to support timely decision-making.

Sosialisasi DBD Bentuk Upaya Pencegahan dan Penurunan Kasus Demam Berdarah di Desa Kebonadem

Socialization on the prevention of Dengue Hemorrhagic Fever (DBD) in Kebonadem Village on July 20 2024 aims to increase public awareness about the dangers of DBD and steps to prevent it. The main problem faced is the high risk of dengue fever transmission due to population density and community behavior that does not maintain environmental cleanliness, which supports the breeding of the Aedes aegypti mosquito. The urgency of this outreach is very high considering that dengue fever cases often cause Extraordinary Events (KLB) and the fatal impacts they can have. The results of this outreach show a significant increase in public understanding regarding preventive measures such as the application of 3M Plus (Draining, Covering, Burying and Sprinkling abate powder) as well as the early signs of dengue fever. Active participation in discussions and implementing new habits, such as cleaning water reservoirs, indicates the positive impact of this activity. Despite progress, consistency in implementing prevention habits and ongoing support from various parties is still needed to ensure long-term success. Regular evaluations will help assess the effectiveness of the program and reduce the number of dengue cases in the village, making it an example of success in dengue prevention in other communities.

Impact of Waste Management on Infectious Disease Control: Evaluating Strategies to Mitigate Dengue Transmission and Mosquito Breeding Sites – A Systematic Review

Background: Dengue, a mosquito-borne viral disease primarily transmitted by Aedes mosquitoes, is a significant global public health concern, particularly in tropical and subtropical regions. Severe cases, including dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), can be fatal. Recent outbreaks in Bangladesh highlight the disease's escalating threat, with inadequate waste management playing a critical role in mosquito breeding and disease transmission. Methods: This review aims to assess the effectiveness of various waste management techniques, such as gasification, pyrolysis, compaction, and incineration, in reducing the buildup of garbage and, therefore, the spread of mosquito breeding grounds. This review also assesses the waste-derived containers used for storing wastewater, which act as breeding grounds for dengue mosquitoes. This review identifies Aedes aegypti mosquito larvae density in ten dengue-endemic regions. Larval samples were collected from various outdoor containers using dipping methods and analyzed through the Container Index (CI). The CI represents the percentage of containers infested with larvae and indicates the potential for dengue transmission. Results: The review revealed that high CI values in locations such as Dire Dawa, Ethiopia (54%), and Tamil Nadu, India (32.2%) indicated significant risk for dengue transmission. In contrast, a low CI value of 0.15% was observed in Rawalpindi, Pakistan, corresponding with lower dengue incidence. Results showed that poorly managed waste sites, particularly those accumulating stagnant water, contributed to higher CI values. Conclusion: Effective waste management, including proper disposal and reduced breeding grounds, is crucial in mitigating dengue transmission. The review emphasizes the need for improved waste management infrastructure, community involvement, and government-led policy frameworks to control Aedes mosquito populations and reduce dengue outbreaks.

Potential climate change effects on the distribution of urban and sylvatic dengue and yellow fever vectors

ABSTRACT Climate change may increase the risk of dengue and yellow fever transmission by urban and sylvatic mosquito vectors. Previous research primarily focused on Aedes aegypti and Aedes albopictus. However, dengue and yellow fever have a complex transmission cycle involving sylvatic vectors. Our aim was to analyze how the distribution of areas favorable to both urban and sylvatic vectors could be modified as a consequence of climate change. We projected, to future scenarios, baseline distribution models already published for these vectors based on the favorability function, and mapped the areas where mosquitoes’ favorability could increase, decrease or remain stable in the near (2041–2060) and distant (2061–2080) future. Favorable areas for the presence of dengue and yellow fever vectors show little differences in the future compared to the baseline models, with changes being perceptible only at regional scales. The model projections predict dengue vectors expanding in West and Central Africa and in South-East Asia, reaching Borneo. Yellow fever vectors could spread in West and Central Africa and in the Amazon. In some locations of Europe, the models suggest a reestablishment of Ae. aegypti, while Ae. albopictus will continue to find new favorable areas. The results underline the need to focus more on vectors Ae. vittatus, Ae. luteocephalus and Ae. africanus in West and Central sub-Saharan Africa, especially Cameroon, Central Africa Republic, and northern Democratic Republic of Congo; and underscore the importance of enhancing entomological monitoring in areas where populations of often overlooked vectors may thrive as a result of climate changes.

Climate change is aggravating dengue and yellow fever transmission risk

Dengue and yellow fever have complex cycles, involving urban and sylvatic mosquitoes, and non‐human primate hosts. To date, efforts to assess the effect of climate change on these diseases have neglected the combination of such crucial factors. Recent studies only considered urban vectors. This is the first study to include them together with sylvatic vectors and the distribution of primates to analyse the effect of climate change on these diseases. We used previously published models, based on machine learning algorithms and fuzzy logic, to identify areas where climatic favourability for the relevant transmission agents could change: 1) favourable areas for the circulation of the viruses due to the environment and to non‐human primate distributions; 2) the favourability for urban and sylvatic vectors. We obtained projections of future transmission risk for two future periods and for each disease, and implemented uncertainty analyses to test for predictions reliability. Areas currently favourable for both diseases could keep being climatically favourable, while global favourability could increase a 7% for yellow fever and a 10% increase for dengue. Areas likely to be more affected in the future for dengue include West Africa, South Asia, the Gulf of Mexico, Central America and the Amazon basin. A possible spread of dengue could take place into Europe, the Mediterranean basin, the UK and Portugal; and, in Asia, into northern China. For yellow fever, climate could become more favourable in Central and Southeast Africa; India; and in north and southeast South America, including Brazil, Paraguay, Bolivia, Peru, Colombia and Venezuela. In Brazil, favourability for yellow fever will probably increase in the south, the west and the east. Areas where the transmission risk spread is consistent to the dispersal of vectors are highlighted in respect of areas where the expected spread is directly attributable to environmental changes. Both scenarios could involve different prevention strategies.

Entomological surveys and insecticide susceptibility profile of Aedes aegypti during the dengue outbreak in Sao Tome and Principe in 2022.

The first dengue outbreak in Sao Tome and Principe was reported in 2022. Entomological investigations were undertaken to establish the typology of Aedes larval habitats, the distribution of Ae. aegypti and Ae. albopictus, the related entomological risk and the susceptibility profile of Ae. aegypti to insecticides, to provide evidence to inform the outbreak response. Entomological surveys were performed in all seven health districts of Sao Tome and Principe during the dry and rainy seasons in 2022. WHO tube and synergist assays using piperonyl butoxide (PBO) and diethyl maleate (DEM) were carried out, together with genotyping of F1534C/V1016I/V410L mutations in Ae. aegypti. Aedes aegypti and Ae. albopictus were found in all seven health districts of the country with high abundance of Ae. aegypti in the most urbanised district, Agua Grande. Both Aedes species bred mainly in used tyres, discarded tanks and water storage containers. In both survey periods, the Breteau (BI > 50), house (HI > 35%) and container (CI > 20%) indices were higher than the thresholds established by WHO to indicate high potential risk of dengue transmission. The Ae. aegypti sampled were susceptible to all insecticides tested except dichlorodiphenyltrichloroethane (DDT) (9.2% mortality, resistant), bendiocarb (61.4% mortality, resistant) and alpha-cypermethrin (97% mortality, probable resistant). A full recovery was observed in Ae. aegypti resistant to bendiocarb after pre-exposure to synergist PBO. Only one Ae. aegypti specimen was found carrying F1534C mutation. These findings revealed a high potential risk for dengue transmission throughout the year, with the bulk of larval breeding occurring in used tyres, water storage and discarded containers. Most of the insecticides tested remain effective to control Aedes vectors in Sao Tome, except DDT and bendiocarb. These data underline the importance of raising community awareness and implementing routine dengue vector control strategies to prevent further outbreaks in Sao Tome and Principe, and elsewhere in the subregion.

Dengue virus transmission risk in blood donation: Evidence from Thailand.

Individuals infected with dengue virus (DENV) often show no symptoms, which raises the risk of DENV transfusion transmission (TT-DENV) in areas where the virus is prevalent. This study aimed to determine the evidence of DENV infection in blood donors from different geographic regions of Thailand. A cross-sectional study was conducted on blood donor samples collected from the Thai Red Cross National Blood Center and four regional blood centers between March and September 2020. Screening for DENV nonstructural protein 1 (NS1), anti-DENV immunoglobulin G (IgG), and IgM antibodies was performed on residual blood from 1053 donors using enzyme-linked immunosorbent assay kits. Positive NS1 and IgM samples indicating acute infection were verified using four different techniques, including quantitative real-time (q) RT-PCR, nested PCR, virus isolation in C6/36 cells, and mosquito amplification. DENV IgG seropositivity was identified in 89% (938/1053) of blood donors. Additionally, 0.4% (4/1053) and 2.1% (22/1053) of Thai blood donors tested positive for NS1 and IgM, respectively. The presence of asymptomatic dengue virus infection in healthy blood donors suggests a potential risk of transmission through blood transfusion, posing a concern for blood safety.

Identifying villages and breeding habitats for dengue transmission in Thailand: insights from long-term larval surveys

BackgroundIn Thailand, the Department of Disease Control (DDC) regularly performs visual larval surveys throughout the country to monitor dengue fever outbreaks. Since 2016, the DDC switched from a paper-based to a digital-based larval survey process. The significant amount of larval survey data collected digitally presents a valuable opportunity to precisely identify the villages and breeding habitats that are vulnerable to dengue transmission.MethodsThe study used digitally collected larval survey data from 2017 to 2019. It employed larval indices to evaluate the risk of dengue transmission in villages based on seasonal, regional, and categorical perspectives. Furthermore, the study comprehensively scrutinized each container category by employing different measures to determine its breeding preference ratio.ResultsThe result showed that villages with a very high-risk of dengue transmission were present year-round in all regions, with the highest proportion during the rainy season. The Southern region had more high-risk villages during the winter season due to rainfall. Slums and residential communities were more vulnerable to dengue than commercial areas. All container categories could potentially serve as breeding habitats for dengue-carrying mosquitoes, with abandoned containers being the most significant breeding sites.ConclusionsThe risk of dengue transmission was present year-round throughout Thailand. This underscores the importance of community and government initiatives, along with sustained public awareness campaigns and active community engagement, to efficiently and permanently eradicate mosquito breeding habitats. It should be noted that larval indices may not strongly correlate with dengue cases, as indicated by the preliminary analysis. However, they offer valuable insights into potential breeding sites for targeted preventive measures.

Crowded and warmer: Unequal dengue risk at high spatial resolution across a megacity of India

The role of climate factors on transmission of mosquito-borne infections within urban landscapes must be considered in the context of the pronounced spatial heterogeneity of such environments. Socio-demographic and environmental variation challenge control efforts for emergent arboviruses transmitted via the urban mosquito Aedes aegypti. We address at high resolution, the spatial heterogeneity of dengue transmission risk in the megacity of Delhi, India, as a function of both temperature and the carrying-capacity of the human environment for the mosquito. Based on previous results predicting maximum mosquitoes per human for different socio-economic typologies, and on remote sensing temperature data, we produce a map of the reproductive number of dengue at a resolution of 250m by 250m. We focus on dengue risk hotspots during inter-epidemic periods, places where chains of transmission can persist for longer. We assess the resulting high-resolution risk map of dengue with reported cases for three consecutive boreal winters. We find that both temperature and vector carrying-capacity per human co-vary in space because of their respective dependence on population density. The synergistic action of these two factors results in larger variation of dengue’s reproductive number than when considered separately, with poor and dense locations experiencing the warmest conditions and becoming the most likely reservoirs off-season. The location of observed winter cases is accurately predicted for different risk threshold criteria. Results underscore the inequity of risk across a complex urban landscape, whereby individuals in dense poor neighborhoods face the compounded effect of higher temperatures and mosquito carrying capacity. Targeting chains of transmission in inter-epidemic periods at these locations should be a priority of control efforts. A better mapping is needed of the interplay between climate factors that are dominant determinants of the seasonality of vector-borne infections and the socio-economic conditions behind unequal exposure.

Modelling the dynamic basic reproduction number of dengue based on MOI of Aedes albopictus derived from a multi-site field investigation in Guangzhou, a subtropical region

BackgroundMore than half of the global population lives in areas at risk of dengue (DENV) transmission. Developing an efficient risk prediction system can help curb dengue outbreaks, but multiple variables, including mosquito-based surveillance indicators, still constrain our understanding. Mosquito or oviposition positive index (MOI) has been utilized in field surveillance to monitor the wild population density of Aedes albopictus in Guangzhou since 2005.MethodsBased on the mosquito surveillance data using Mosq-ovitrap collection and human landing collection (HLC) launched at 12 sites in Guangzhou from 2015 to 2017, we established a MOI-based model of the basic dengue reproduction number (R0) using the classical Ross-Macdonald framework combined with a linear mixed-effects model.ResultsDuring the survey period, the mean MOI and adult mosquito density index (ADI) using HLC for Ae. albopictus were 12.96 ± 17.78 and 16.79 ± 55.92, respectively. The R0 estimated from the daily ADI (ADID) showed a significant seasonal variation. A 10-unit increase in MOI was associated with 1.08-fold (95% CI 1.05, 1.11) ADID and an increase of 0.14 (95% CI 0.05, 0.23) in the logarithmic transformation of R0. MOI-based R0 of dengue varied by month and average monthly temperature. During the active period of Ae. albopictus from April to November in Guangzhou region, a high risk of dengue outbreak was predicted by the MOI-based R0 model, especially from August to October, with the predicted R0 > 1. Meanwhile, from December to March, the estimates of MOI-based R0 were < 1.ConclusionsThe present study enriched our knowledge about mosquito-based surveillance indicators and indicated that the MOI of Ae. albopictus could be valuable for application in estimating the R0 of dengue using a statistical model. The MOI-based R0 model prediction of the risk of dengue transmission varied by month and temperature in Guangzhou. Our findings lay a foundation for further development of a complex efficient dengue risk prediction system.Graphical

Density of Aedes aegypti and dengue virus transmission risk in two municipalities of Northwestern Antioquia, Colombia.

The high infestation of Aedes aegypti populations in Urabá, Antioquia, Colombia represents a risk factor for increased dengue morbidity and mortality. This study aimed to determine the risk of dengue transmission by estimating the population of Ae. aegypti using entomological indices, density of females per dwelling and inhabitant, and virological surveillance in two municipalities in Colombia. A cross-sectional study was conducted with quarterly entomological surveys in three neighborhoods of Apartadó and Turbo between 2021 and 2022. Aedes indices and vector density per dwelling and per inhabitant were calculated. The Kernel method was used for spatial analysis, and correlations between climatic variables and mosquito density were examined. Virus detection and serotyping in mosquitoes was performed using single-step reverse transcription polymerase chain reaction. The housing, reservoir, and Breteau indices were 48.9%, 29.5%, and 70.2%, respectively. The mean density of Ae. aegypti was 1.47 females / dwelling and 0.51 females / inhabitant. The overall visual analysis showed several critical points in the neighborhoods studied. There was significant correlation of vector density and relative humidity and precipitation in the neighborhoods 29 de noviembre and 24 de diciembre. Additionally, serotypes DENV-1 and DENV-2 were found. The overall indices for dwellings, reservoirs, and Breteau were lower than those recorded in 2014 in Urabá. The vector density results in this study were similar to those reported in other studies conducted in Latin America, and vector infection was detected. The Aedes and density indices are complementary, emphasizing the importance of continuous surveillance of Ae. aegypti to inform appropriate control strategies and prevent future dengue outbreaks in these municipalities.

The introduction and establishment of dengue disease in a new area: a mini review

Dengue fever virus is a mosquito-borne virus that poses a significant public health threat worldwide. Dengue virus is primarily transmitted by the Aedes mosquitoes, which develop in small man-made containers in urban environments. Climate change and urbanization have contributed to the spread of the Aedes mosquitoes, increasing the risk of dengue virus transmission in densely populated areas. Increasing the transmission of virus by Aedes mosquitoes increases the dengue infection. Additionally, factors such as poor sanitation, low community immunity levels, inadequate waste management and a lack of access to healthcare can also impact the establishment and spread of dengue fever. Globalization, international travel and tourism can introduce the virus to new regions and contribute to its establishment. These factors create ideal conditions for the Aedes mosquitoes to develop and for the dengue virus to establish and spread, posing a significant public health challenge.

Stegomyia indices and pattern recognition of Aedes aegypti (Diptera: Culicidae) in selected agrogeoclimatic zones of Punjab, Pakistan

Mosquito-borne diseases especially, dengue is gaining currency nowadays in Pakistan. As there is no approved dengue vaccine available worldwide, prevention and control of vector is the only solution amid prevailing circumstances. The present study is a maiden attempt to screen indoor and outdoor breeding containers for the presence of Aedes (Ae.) aegypti larvae from selected study districts of Punjab, Pakistan i.e., Dera Ghazi Khan (DG Khan), Chakwal, and Faisalabad. A total of 384 houses from each study districts were surveyed for a calendar year. Mosquito larvae were collected, preserved, and identified using standard taxonomic keys. House Index (HI), Container Index (CI), and Breteau Index (BI) were estimated. Chi-square analysis was applied to calculate the association between Ae. aegypti larvae and breeding containers. Chakwal was identified with the highest values of Stegomyia indices (HI = 46.61 %, BI = 91.67 %, and CI = 15.28 %) followed by Faisalabad (HI = 34.11 %, BI = 68.75 % and, CI = 13.04 %) and DG Khan (HI = 28.39 %, BI = 68.23 % and, CI = 11.29 %). Earthen jars, tree holes, and water tanks were found significantly (p < 0.05) associated with the abundance of larvae irrespective of the geographical location. However, flower tubs and plastic buckets were found significantly (p < 0.05) associated in Faisalabad and Chakwal while, tyres and plastic bottles were found associated (p < 0.05) with the abundance of Ae. aegypti larvae in Faisalabad and DG Khan. These findings will help the stakeholders to devise appropriate preventive measures in combating the risk of dengue transmission.

Prevalence of dengue fever in Saudi Arabia: Jeddah as a case study

AbstractDengue fever is widespread in tropical and subtropical regions, including Saudi Arabia. Aedes aegypti (Diptera: Culicidae) transmits dengue and many other diseases, including chikungunya and Zika. This study provides an overview of dengue fever in Saudi Arabia since the first case was recorded in the early 1990s. In addition, it focuses on the epidemiological situation in Jeddah as a case study to study the spatial distribution of dengue cases using Geographic Information Systems (GIS) techniques over 5 years, from 2019 to 2023. The first recorded case in Saudi Arabia was in October 1993; however, daily data indicates that 2023 is a major epidemic year. The number of infections has reached 4099 so far during the first half of the year, which indicates a significant increase compared to previous years. GIS analysis has unveiled the locations of high infection rates across multiple municipalities, commonly called hotspots, and identified areas where dengue cases remain relatively low. The Inverse Distance Weighted (IDW) tool was used to determine the severity of infection in different areas of Jeddah. The study concluded that factors such as temperature, rainfall, and septic tanks in areas that lack a proper sanitation network are the most contributing factors to the spread of disease vectors and, thus, dengue. Winter rainfall creates conducive breeding environments for dengue mosquito vectors, increasing transmission rates. On the other hand, summer heat accelerates the mosquito life cycle and enhances viral replication, heightening the risk of dengue transmission.

Spatial analysis for risk assessment of dengue in Spain

IntroductionThe establishment of Aedes albopictus in new areas in Europe has changed the risk of local dengue transmission represented by imported human cases. The risk of transmission is determined by the distribution of travelers arriving from dengue-endemic areas and the distribution of Ae. albopictus as potential vectors of dengue in Spain. MethodsEnvironmental, entomological, epidemiological, demographic, tourism and travel data were analyzed to produce a series of maps to represent: the distribution of Ae. albopictus across municipalities; the risk of expansion of Ae. albopictus based on a species distribution model; the calculated index of travelers from dengue-endemic areas (IDVZE) per province; the percentage contribution of each municipality to the total number of cases in Spain. The maps were then added using map algebra, to profile the spatial risk of autochthonous dengue in Spain at a municipal level from 2016 to 2018. ResultsAe. albopictus was detected in 983 municipalities. The calculated IDVZE varied from 0.23 to 10.38, with the highest IDVZE observed in Madrid. The overall risk of autochthonous cases oscillated between 0.234 and 115, with the very high risk and high risk areas detected in the Mediterranean region, mainly in the Levantine coast and some parts of the Balearic Islands. Most of the interior of the peninsula was characterized as low risk. ConclusionPrevention and control measures to mitigate the risk of autochthonous dengue should be prioritized for municipalities in the high risk areas integrating early detection of imported dengue cases and vector control.

Relationship Between Mosquito Nest Eradication Practice and The Existence of Larvae Aedes Aegypti with Dengue Incidence in Penjaringan District, North Jakarta

Dengue Hemorrhagic Fever (DHF) is a public health problem in Indonesia and still often causes extraordinary events with a high mortality rate. All regions in Indonesia are at risk of contracting dengue disease, because the virus that causes and mosquitoes has spread widely in residential and public places in Indonesia. Penjaringan District North Jakarta City has 70% densely populated residential areas, so it has a risk for dengue disease transmission. The sample in this study amounted to 80 people, with a division of 40 case groups and 40 control groups. This research uses observational analytical design with case control method. The variables studied were Mosquuito Nest Eradication practice and the presence of larvae. Data on Mosquuito Nest Eradication Behavior-DHF variables were obtained through questionnaires and variable data on the presence of larvae were obtained through direct observation of the environment around the respondent's house. Based on the results of Chi Square analysis showed that the practice of Mosquuito Nest Eradication (p = 0.007) and the presence of larvae (p = 0.047) had a significant relationship. Respondents who are lacking in Mosquuito Nest Eradication practice are at 5,952 times greater risk of developing DHF compared to people who are good in Mosquuito Nest Eradication practice. There is a relationship between the practice of Mos and the existence of larvae with dengue incidence in densely populated settlements in Penjaringan District, North Jakarta. The community should pay attention to the eradication of their nest by conducting the 3M Plus program regularly

Spatial analysis for risk assessment of dengue in Spain

IntroductionThe establishment of Aedes albopictus in new areas in Europe has changed the risk of local dengue transmission represented by imported human cases. The risk of transmission is determined by the distribution of travelers arriving from dengue-endemic areas and the distribution of Ae. albopictus as potential vectors of dengue in Spain. MethodsEnvironmental, entomological, epidemiological, demographic, tourism and travel data were analyzed to produce a series of maps to represent: the distribution of Ae. albopictus across municipalities; the risk of expansion of Ae. albopictus based on a species distribution model; the calculated index of travelers from dengue-endemic areas (IDVZE) per province; the percentage contribution of each municipality to the total number of cases in Spain. The maps were then added using map algebra, to profile the spatial risk of autochthonous dengue in Spain at a municipal level from 2016 to 2018. ResultsAe. albopictus was detected in 983 municipalities. The calculated IDVZE varied from 0.23 to 10.38, with the highest IDVZE observed in Madrid. The overall risk of autochthonous cases oscillated between 0.234 and 115, with the very high risk and high risk areas detected in the Mediterranean region, mainly in the Levantine coast and some parts of the Balearic Islands. Most of the interior of the peninsula was characterized as low risk. ConclusionPrevention and control measures to mitigate the risk of autochthonous dengue should be prioritized for municipalities in the high risk areas integrating early detection of imported dengue cases and vector control.

Combination patterns of precipitation and its concentration degree determining the risk of dengue outbreaks in China

The amount and distribution of precipitation can determine dengue risk by affecting mosquito breeding; however, previous studies failed to incorporate this bivariate characteristic to examine dengue fever transmission. In the present research, nationwide data on daily dengue cases in China between January 2005 and December 2020 were obtained, and the top 12 cities accounting for 78% of total cases were selected for analysis. Precipitation patterns were quantified by weekly precipitation and precipitation concentration degree (PCD). On the basis of the combinations of both parameters, the exposure-response relationships of precipitation with dengue risk were established using generalised additive models, and the high-dengue-risk thresholds of precipitation patterns were further identified. Dengue burden was assessed by calculating attributable dengue cases. For the same amount of precipitation, the dispersed precipitation in the pre-summer rainy season leads to a higher dengue risk in autumn. The weekly precipitation of 100–150 mm and PCD of 0.2–0.4 constitute the highest risk scenario, and the average frequency of precipitation associated with dengue risk in 2013–2020 is 1.6 times higher than that in 2005–2012. A total of 3093 attributable dengue cases are identified. From 2005 to 2020, the amount of dispersed precipitation increased in southern and southwestern China and posed high dengue risks in central China. This study has improved the understanding of the health impacts of irregular rainfall under climate change. Our approach to identifying thresholds provides information for early warning systems and helps reduce the risk of dengue transmission in the long run.

Dengue 1 outbreak in Rosso, northern Senegal, October 2021: entomologic investigations.

Senegal has experienced periodic epidemics of dengue in urban areas with increased incidence in recent years. However, few data are available on the local ecology of the epidemic vectors. In October 2021, a dengue outbreak was reported in northern Senegal to the Institute Pasteur de Dakar. Entomologic investigations then were undertaken to identify the areas at risk of transmission and to identify the vector(s). Adult mosquitoes were collected indoors and outdoors at selected households, while containers with water were inspected for mosquito larvae. All the Aedes aegypti (L.) collected were tested for dengue virus NS1 protein using a rapid diagnostic test (RDT), and positive samples were confirmed by real-time RT-PCR. The qRT-PCR positive samples were subjected to whole genome sequencing using Nanopore technology. The majority of the larvae-positive containers (83.1%) were used for water storage. The Breteau and Container indices exceeded the WHO-recommended thresholds for the risk of dengue virus transmission except at 2 localities. Ae. aegypti, the only reputed dengue vector, was collected resting indoors as well as outdoors and biting during the day and night. The NS1 protein was detected in 22 mosquito pools, including one pool of females emerging from field-collected larvae. All NS1-positive results were confirmed by RT-PCR. Virus serotyping showed that the outbreak was caused by DENV-1. This study demonstrates the need for continuous control of adult and aquatic stages of Ae. aegypti to prevent future dengue epidemics in Senegal. RDTs appear to be a promising tool for dengue diagnostics and surveillance.

Risk of dengue, Zika, and chikungunya transmission in the metropolitan area of Cucuta, Colombia: cross-sectional analysis, baseline for a cluster-randomised controlled trial of a novel vector tool for water containers

BackgroundArbovirus diseases such as dengue, Zika, and chikungunya are a public health threat in tropical and subtropical areas. In the absence of a vaccine or specific treatment, vector management (in this case the control of the primary vector Aedes aegypti) is the best practice to prevent the three diseases. A good understanding of vector behaviour, ecology, human mobility and water use can help design effective vector control programmes. This study collected baseline information on these factors for identifying the arbovirus transmission risk and assessed the requirements for a large intervention trial in Colombia.MethodsBaseline surveys were conducted in 5,997 households, randomly selected from 24 clusters (neighbourhoods with on average 2000 houses and 250 households inspected) in the metropolitan area of Cucuta, Colombia. The study established population characteristics including water management and mobility as well as larval-pupal indices which were estimated and compared in all clusters. Additionally, the study estimated disease incidence from two sources: self-reported dengue cases in the household survey and cases notified by the national surveillance system.ResultsIn all 24 study clusters similar social and demographic characteristics were found but the entomological indicators and estimated disease incidence rates varied. The entomological indicators showed a high vector infestation: House Index = 25.1%, Container Index = 12.3% and Breteau Index = 29.6. Pupae per person Index (PPI) as an indicator of the transmission risk showed a large range from 0.22 to 2.04 indicating a high transmission risk in most clusters. The concrete ground tanks for laundry –mostly outdoors and uncovered- were the containers with the highest production of Ae. aegypti as 86.3% of all 17,613 pupae were identified in these containers. Also, the annual incidence of dengue was high: 841.6 self-reported cases per 100,000 inhabitants and the dengue incidence notified by the National surveillance system was 1,013.4 cases per 100,000 in 2019. Only 2.2% of the households used container water for drinking. 40.3% of the study population travelled during the day (when Aedes mosquitoes bite) outside their clusters.ConclusionsThe production of Ae. aegypti mosquitoes occurred almost exclusively in concrete ground tanks for laundry (lavadero), the primary intervention target. The baseline study provides necessary evidence for the design and implementation of a cluster randomized intervention trial in Colombia.