Climate Suitable Conditions Index and Autochthonous Dengue Infections: an Early Warning Index

Background: Aedes aegypti is the primary vector of dengue and contributes to most major epidemics of this virus worldwide. Aedes albopictus is also blamed for certain epidemics, as the 2014 Guangdong dengue outbreak. In Guangdong province, Ae. albopictus is thought to be the dominant vector species, with Ae. aegypti absent from most areas. Whether or not primary mosquito vectors are present, optimal climatic conditions for dengue vector species may play a substantial role in epidemics of the virus. We hypothesise that although vector species are required to initiate and establish an outbreak, favourable weather conditions may then grow and perpetuate the outbreak via complex effects on vector sympatry or interactions.Methods: Vector spices-specific suitable conditions index (SCI) and autochthonous dengue case data were fitted to negative binomial (NB) regression models. After accounting for potential confounders, we assessed the relationship between SCI and autochthonous dengue cases. We assumed SCI interaction was a proxy for vector species sympatry and SCI difference a proxy for interspecies competition. Finally, we explored the relationship between these assumed conditions and the autochthonous dengue case. Results: Autochthonous dengue cases are associated negatively with SCI for Ae.albopictus and positively with SCI for Ae.aegypti. According to the NB regression models, autochthonous dengue cases increased 4% (Incident Rate Ratio (IRR): 1.04, 95% CI: 1.02, 1.06) for every unit increase in SCI for Ae. aegypti, but decreased by 3% (IRR: 0.97, 95% CI: 0.96, 0.99) for Ae. albopictus SCI. There was also an interaction between two SCIs and a positive effect of the difference in SCIs on autochthonous dengue cases. These findings support the hypothesis that vector sympatry and interactions may influence the risk of a dengue outbreak.Conclusions: Our results confirm the hypothesis that the dengue virus is more transmissible in regions with warmer weather conditions (high SCI for Ae. aegypti). SCI of Ae. aegypti would be a valuable index to predict dengue transmission even in the absence of Ae. aegypti but with Ae. albopictus present. The results also support that the SCI is beneficial for evaluating dengue outbreak risk in terms of vector sympatry and interactions in the absence of entomology data in future research.

Validation of the Early Warning and Response System (EWARS) for dengue outbreaks: Evidence from the national vector control program in Mexico

Background During 2017, twenty health districts (locations) implemented a dengue outbreak Early Warning and Response System (EWARS) in Mexico, which processes epidemiological, meteorological and entomological alarm indicators to predict dengue outbreaks and triggers early response activities. Out of the 20 priority districts where more than one fifth of all national disease transmission in Mexico occur, eleven districts were purposely selected and analyzed. Nine districts presented outbreak alarms by EWARS but without subsequent outbreaks (“non-outbreak districts”) and two presented alarms with subsequent dengue outbreaks (“outbreak districts”). This evaluation study assesses and compares the impact of alarm-informed response activities and the consequences of failing a timely and adequate response across the outbreak groups. Methods Five indicators of dengue outbreak response (larval control, entomological studies with water container interventions, focal spraying and indoor residual spraying) were quantitatively analyzed across two groups (”outbreak districts” and “non-outbreak districts”). However, for quality control purposes, only qualitative concluding remarks were derived from the fifth response indicator (fogging). Results The average coverage of vector control responses was significantly higher in non-outbreak districts and across all four indicators. In the “outbreak districts” the response activities started late and were of much lower intensity compared to “non-outbreak districts”. Vector control teams at districts-level demonstrated diverse levels of compliance with local guidelines for ‘initial’, ‘early’ and ‘late’ responses to outbreak alarms, which could potentially explain the different outcomes observed following the outbreak alarms. Conclusion Failing timely and adequate response of alarm signals generated by EWARS showed to negatively impact the disease outbreak control process. On the other hand, districts with adequate and timely response guided by alarm signals demonstrated successful records of outbreak prevention. This study presents important operational scenarios when failing or successding EWARS but warrants investigating the effectiveness and cost-effectiveness of EWARS using a more robust designs.

Analysis of international traveler mobility patterns in Tokyo to identify geographic foci of dengue fever risk

Travelers play a role in triggering epidemics of imported dengue fever because they can carry the virus to other countries during the incubation period. If a traveler carrying dengue virus visits open green space and is bitten by mosquitoes, a local outbreak can ensue. In the present study, we aimed to understand the movement patterns of international travelers in Tokyo using mobile phone data, with the goal of identifying geographical foci of dengue transmission. We analyzed datasets based on mobile phone access to WiFi systems and measured the spatial distribution of international visitors in Tokyo on two specific dates (one weekday in July 2017 and another weekday in August 2017). Mobile phone users were classified by nationality into three groups according to risk of dengue transmission. Sixteen national parks were selected based on their involvement in a 2014 dengue outbreak and abundance of Aedes mosquitoes. We found that not all national parks were visited by international travelers and that visits to cemeteries were very infrequent. We also found that travelers from countries with high dengue prevalence were less likely to visit national parks compared with travelers from dengue-free countries. Travelers from countries with sporadic dengue cases and countries with regional transmission tended to visit common destinations. By contrast, the travel footprints of visitors from countries with continuous dengue transmission were focused on non-green spaces. Entomological surveillance in Tokyo has been restricted to national parks since the 2014 dengue outbreak. However, our results indicate that areas subject to surveillance should include both public and private green spaces near tourist sites.

The emergence of Dengue Fever in Sheikhupura, Pakistan: its seroprevalence and risk factors assessment during 2014-2017

Introduction: District Sheikhupura encountered its first dengue outbreak in 2014 but lacked serological evidence and reports of risk factors associated with it. To assess this, a hospital-based study was conducted from January 2014 to December 2017. Methodology: Blood from 333 participants was collected, the serum obtained was tested for IgG and IgM antibodies against DENV using a commercially available ELISA kit. Results: The results showed that out of all (n= 333) samples tested, 120 were turned up positive for DENV, making an overall prevalence of 36%. Of the 120 confirmed cases, 55% (n = 66) were recorded in 2014, 10% (n = 12) in 2015, 27.5% (n = 33) in 2016, and 7.5% (n = 9) in 2017. It was found that 68.3% (n = 82) were male and 31.7% (n = 38) were female, with 61% (n = 74) patients aged between 11-30 years. The highest prevalence of infection, 94.2% (n = 113), was noted after the rainy season. During the study, the highest number of cases appeared in Ferozewala Tehsil. The factors age, gender, and season were found statistically significant with the prevalence of infection (p < 0.05). Conclusions: The study is the first report on the detection of dengue in the Sheikhupura district. The survey anticipated its geographical expansion, determined associated risk factors, and suggests active disease surveillance in the area.

A dengue outbreak in a rural community in Northern Coastal Ecuador: An analysis using unmanned aerial vehicle mapping

Dengue is recognized as a major health issue in large urban tropical cities but is also observed in rural areas. In these environments, physical characteristics of the landscape and sociodemographic factors may influence vector populations at small geographic scales, while prior immunity to the four dengue virus serotypes affects incidence. In 2019, a rural northwestern Ecuadorian community, only accessible by river, experienced a dengue outbreak. The village is 2–3 hours by boat away from the nearest population center and comprises both Afro-Ecuadorian and Indigenous Chachi households. We used multiple data streams to examine spatial risk factors associated with this outbreak, combining maps collected with an unmanned aerial vehicle (UAV), an entomological survey, a community census, and active surveillance of febrile cases. We mapped visible water containers seen in UAV images and calculated both the green-red vegetation index (GRVI) and household proximity to public spaces like schools and meeting areas. To identify risk factors for symptomatic dengue infection, we used mixed-effect logistic regression models to account for the clustering of symptomatic cases within households. We identified 55 dengue cases (9.5% of the population) from 37 households. Cases peaked in June and continued through October. Rural spatial organization helped to explain disease risk. Afro-Ecuadorian (versus Indigenous) households experience more symptomatic dengue (OR = 3.0, 95%CI: 1.3, 6.9). This association was explained by differences in vegetation (measured by GRVI) near the household (OR: 11.3 95% 0.38, 38.0) and proximity to the football field (OR: 13.9, 95% 4.0, 48.4). The integration of UAV mapping with other data streams adds to our understanding of these dynamics.