Inapparent dengue in a community living among dengue-positive Aedes mosquitoes and in a hospital in Klang Valley, Malaysia

Synthesis of Isolated DNA Aptamer and Its Application of AC-Electrothermal Flow-Based Rapid Biosensor for the Detection of Dengue Virus in a Spiked Sample

Dengue fever is an infectious disease caused by the dengue virus (DENV) and is transmitted by mosquitoes in tropical and subtropical regions. The early detection method at a low cost is essential. To address this, we synthesized the isolated DENV aptamer for fabricating a rapid electrochemical biosensor on a Au interdigitated microgap electrode (AuIMGE). The DENV aptamers were generated using the SELEX (systemic evolution of ligands by exponential enrichment) method for binding to DENV surface envelope proteins. To reduce the manufacturing cost, unnecessary nucleotide sequences were excluded from the isolation process of the DENV aptamer. To reduce the detection time, the alternating current electrothermal flow (ACEF) technique was applied to the fabricated biosensor, which can shorten the detection time to 10 min. The performance of the biosensor was evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In the diluted DENV protein solution, the linear range of the concentrations was from 1 pM to 1 μM and the LOD was 76.7 fM. Moreover, the proposed biosensor detected DENV in a diluted spiked sample at a linear range of 10-6 to 106 TCID50/mL, while the detection performance was proven with an LOD of 1.74 × 10-7 TCID50/mL along with high selectivity.

Knowledge, attitudes and practices of dengue prevention between dengue sustained hotspots and non-sustained hotspots in Singapore: a cross-sectional study

Dengue sustained hotspots (SHS) have resulted in a significant public health burden. In our study, we aimed to (1) compare knowledge, attitudes and practices (KAP) scores between SHS and non-sustained hotspots (NSHS); and (2) identify and describe gaps and factors associated with KAP of dengue prevention among SHS residents residing in Singapore. A cross-sectional study with convenience sampling was conducted using digital survey in randomly selected SHS and NSHS residential areas, consisting of residents aged 21 or older and who had been residing in their existing housing unit in 2019 and 2020. Chi-square test and T-test were used for comparison analysis of categorical and continuous variables, respectively. A total of 466 respondents completed the self-administered, anonymous survey. There were no significant difference in mean scores for Knowledge [SHS(24.66) vs. NSHS(24.37); P: 0.18], Attitudes [SHS(10.38) vs NSHS(10.16); P: 0.08] and Practices [SHS(9.27) vs NSHS(8.80); P: 0.16] sections. Significant SHS-associated factors identified were age group 41-50 years old [95%CI: 1.25-5.03], Malay (95%CI: 0.17-0.98), up to secondary school education (95%CI: 0.07-0.65), private condominium (95%CI: 1.17-3.39), residing in same household unit for 2-5 years (95%CI: 2.44-6.88), respondents who know that mosquito can breed in open container with stagnant water (95%CI: 0.06-0.98), disagree that reducing Aedes mosquitoes is the only way to prevent dengue: (95%CI: 1.19-3.00) and go to clinic/hospital even without severe symptoms: (95%CI: 0.39-0.95). These independent factors associated with dengue sustained hotspots may influence the risk of dengue transmission in residential areas.

Wolbachia in Dengue Control: A Systematic Review

BACKGROUND: Dengue fever outbreaks have been an important public health issue causing high morbidity and mortality, and serious economic effects, particularly in Asia. Control strategies are a challenge to be implemented due to a variety of factors. However, new approaches such as Wolbachia-infected Aedes aegypti have been shown to successfully lowering the life spans of the mosquito, eggs resistance, and disease transmission capabilities. Field trials are still on-going, and there are data to support its benefit in a large population. This systematic review aims to determine the current progress and impact of using Wolbachia in curbing dengue cases in high dengue case locations worldwide. METHODOLOGY: The study uses the Preferred Reporting Items for Systematic reviews and Meta-Analyses review protocol, while the formulation of the research question was based on population of interest, comparison, and outcome. The selected databases include Web of Science, Scopus, PubMed, SAGE, and EBSCOhost. A thorough identification, screening, and included process were done and the results retrieved four articles. These articles were then ranked based on quality using mixed methods appraisal tool. RESULTS: A total of four articles were included from 2019 and 2020 reports in both dengue- and non-dengue-endemic settings. In this review, comparisons in terms of the hierarchy of the study design, community engagement and acceptance, Wolbachia-infected A. aegypti deployment, entomological outcome, and epidemiological outcomes were detailed. All four studies showed a decrease in dengue incidence in Wolbachia-intervention populations. CONCLUSION: Wolbachia programs have been shown to be an effective method in combating dengue diseases. Strong community engagement and involvement from multidisciplinary teams are important factors to ensure the effectiveness and good outcomes of the program.

Dengue surveillance using gravid oviposition sticky (GOS) trap and dengue non-structural 1 (NS1) antigen test in Malaysia: randomized controlled trial

Dengue remains a major public threat and existing dengue control/surveillance programs lack sensitivity and proactivity. More efficient methods are needed. A cluster randomized controlled trial was conducted for 18 months to determine the efficacy of using a combination of gravid oviposition sticky (GOS) traps and dengue non-structural 1 (NS1) antigen for early surveillance of dengue among Aedes mosquito. Eight residential apartments were randomly assigned into intervention and control groups. GOS traps were placed at the intervention apartments weekly to trap Aedes mosquitoes and these tested for dengue NS1 antigen. When dengue-positive pool was detected, the community were notified and advised to execute protective measures. Fewer dengue cases were recorded in the intervention group than the control. Detection of NS1-positive mosquitoes was significantly associated with GOS Aedes index (r_s = 0.68, P < 0.01) and occurrence of dengue cases (r_s = 0.31, P < 0.01). Participants' knowledge, attitude, and practice (KAP) toward dengue control indicated significant improvement for knowledge (P < 0.01), practice (P < 0.01) and total scores (P < 0.01). Most respondents thought this surveillance method is good (81.2%) and supported its use nationwide. Thus, GOS trap and dengue NS1 antigen test can supplement the current dengue surveillance/control, in alignment with the advocated integrated vector management for reducing Aedes-borne diseases.

Field efficacy of palm oil-based nanoemulsion insecticides against Aedes aegypti in Malaysia

This study evaluates the efficacy of palm oil-based nanoemulsion insecticides in thermal fogging applications against adult Ae. aegypti. The nanoemulsion formulations contained a palm oil methyl ester solvent, water, a non-ionic surfactant, and active ingredient deltamethrin, with nanoemulsion droplet diameters ranging from 362 to 382 nm. Knockdown and mortality rates of caged mosquitoes were measured at various distances up to 18 m from the spray nozzle. After 15 min of insecticide exposure, nanoemulsion insecticides achieved a knockdown rate of >97% at a spraying distance of 4 m, and the knockdown effect increased substantially with exposure time. At an 18 m spraying distance, the best nanoemulsion formulation, NanoEW8, achieved a high mosquito mortality rate of more than 80%, whereas the non-nanoemulsion and the commercial product reached only 14 and 8 m distances, respectively, for comparable mortality. The artificial neural network (ANN) was used to predict the mosquito knockdown distribution over the spraying distances and time intervals. The models predicted that NanoEW8 can still cause knockdown at a maximum distance of 61.5 m from the discharge point 60 min after spraying. The results established that Ae. aegypti was susceptible to the newly developed palm oil-based nanoemulsion insecticide, indicating a high potential for mosquito control.

Dengue fever and insecticide resistance in Aedes mosquitoes in Southeast Asia: a review

Dengue fever is the most important mosquito-borne viral disease in Southeast Asia. Insecticides remain the most effective vector control approach for Aedes mosquitoes. Four main classes of insecticides are widely used for mosquito control: organochlorines, organophosphates, pyrethroids and carbamates. Here, we review the distribution of dengue fever from 2000 to 2020 and its associated mortality in Southeast Asian countries, and we gather evidence on the trend of insecticide resistance and its distribution in these countries since 2000, summarising the mechanisms involved. The prevalence of resistance to these insecticides is increasing in Southeast Asia, and the mechanisms of resistance are reported to be associated with target site mutations, metabolic detoxification, reduced penetration of insecticides via the mosquito cuticle and behavioural changes of mosquitoes. Continuous monitoring of the status of resistance and searching for alternative control measures will be critical for minimising any unpredicted outbreaks and improving public health. This review also provides improved insights into the specific use of insecticides for effective control of mosquitoes in these dengue endemic countries.