Dengue is the most prevalent arboviral disease of humans. The host and virus variables associated with dengue virus (DENV) transmission from symptomatic dengue cases (n = 208) to Aedes aegypti mosquitoes during 407 independent exposure events was defined. The 50% mosquito infectious dose for each of DENV-1-4 ranged from 6.29 to 7.52 log10 RNA copies/mL of plasma. Increasing day of illness, declining viremia, and rising antibody titers were independently associated with reduced risk of DENV transmission. High early DENV plasma viremia levels in patients were a marker of the duration of human infectiousness, and blood meals containing high concentrations of DENV were positively associated with the prevalence of infectious mosquitoes 14 d after blood feeding. Ambulatory dengue cases had lower viremia levels compared with hospitalized dengue cases but nonetheless at levels predicted to be infectious to mosquitoes. These data define serotype-specific viremia levels that vaccines or drugs must inhibit to prevent DENV transmission.engue is globally the most important mosquito-borne viral disease of humans, with a global burden of ∼100 million cases per annum (1, 2). Aedes aegypti mosquitoes are the primary mosquito vectors of dengue viruses (DENV), of which there are four virus types (DENV-1-4). Multiple factors influence the likelihood of infection and dissemination of DENV in Ae. aegypti and include the amplitude of daily temperature fluctuations (3), mean temperature (4), and the genotype of mosquito and virus (5), among others (6). The extrinsic incubation period (EIP), a critical determinant of vector competence (7,8), is widely accepted to be 7-14 d for DENV in Ae. aegypti, although a recent modeling analysis of historical DENV transmission data has suggested a wider range of 2-15 d at 30°C (9). A major caveat to many of these observations is that they stem from laboratory experiments with artificially generated virus-spiked blood meals and often in-bred colony mosquitoes.The temporal and virological variables associated with the transmission of DENV from a naturally infected human to a biting Ae. aegypti mosquito are poorly understood. Natural history studies of experimental DENV infection of small cohorts of human volunteers in the 1920s by Siler et al. (10,11), likely using DENV-4 (12), and subsequent studies by Simmons et al. (13), likely using DENV-1 (12), suggested that the window of time before the onset of clinical symptoms that DENV-1 or DENV-4 could be transmitted to Ae. aegypti mosquitoes was 6-18 h or 2 d, respectively (14). After fever onset, the duration of infectiousness was 4-5 d for DENV-1 and up to 2 d for DENV-4, with an EIP in the mosquito of 10 d or more. Consistent with this, mosquitobiting studies by Gubler et al. in the 1960s (15-18) collectively estimated that dengue cases were infectious for 4-5 d after illness onset (range, 2-12 d). The human viremia level required to infect Ae. aegypti mosquitoes is unknown, and therefore it is uncertain what percentage of symptomatic (or asymptomatic...

Dengue is mosquito-borne virus infection that annually causes ~50 million clinically apparent cases worldwide. An internally controlled one-step real-time multiplex RT-PCR assay was developed for detection and quantitation of DENV RNA in plasma sample by using specific primers and fluorogenic TaqMan probes. All primers and probes targeted sequences near the 3′ end of the NS5 gene. The method comprised two multiplex assays and was validated for sensitivity, specificity, linearity, reproducibility and precision. An internal control template was spiked into each clinical specimen to provide quality assurance for each experimental step. The assay allowed for detection of between 0.5 and 3 infectious particles per mL, is rapid and has been operationally characterized in 287 Vietnamese dengue patients from two therapeutic intervention trials at the Hospital for Tropical Diseases, Ho Chi Minh City, Viet Nam.

This study defined the genetic epidemiology of dengue viruses (DENV) in two pivotal phase III trials of the tetravalent dengue vaccine, CYD-TDV, and thereby enabled virus genotype-specific estimates of vaccine efficacy (VE). Envelope gene sequences (n = 661) from 11 DENV genotypes in 10 endemic countries provided a contemporaneous global snapshot of DENV population genetics and revealed high amino acid identity between the E genes of vaccine strains and wild-type viruses from trial participants, including at epitope sites targeted by virus neutralising human monoclonal antibodies. Post-hoc analysis of all CYD14/15 trial participants revealed a statistically significant genotype-level VE association within DENV-4, where efficacy was lowest against genotype I. In subgroup analysis of trial participants age 9–16 years, VE estimates appeared more balanced within each serotype, suggesting that genotype-level heterogeneity may be limited in older children. Post-licensure surveillance is needed to monitor vaccine performance against the backdrop of DENV sequence diversity and evolution.

Adjunctive treatment to improve outcome from bacterial meningitis has centered on dexamethasone. Among Vietnamese patients with bacterial meningitis, cerebrospinal fluid (CSF) opening pressure and CSF:plasma glucose ratios were significantly improved and levels of CSF cytokines interleukin (IL)-6, IL-8, and IL-10 and were all statistically significantly lower after treatment in patients who were randomized to dexamethasone, compared with levels in patients who received placebo.

Transmission of dengue virus (DENV) from mosquito to human is dependent upon the survival of the mosquito beyond the virus extrinsic incubation period. Previous studies report conflicting results of the effects of DENV on Aedes aegypti survival. Here, we describe the effect of DENV on the short-term survival (up to 12 d) of 4,321 Ae. aegypti mosquitoes blood-fed on 150 NS1-positive dengue patients hospitalized in the Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam. Mosquito survival was not different between cohorts that fed upon blood from which 0% of mosquitoes became DENV infected (N = 88 feeds), or 100% became infected (N = 116 feeds). Subgroup analysis also did not reveal serotype-dependent differences in survival, nor a relationship between survival and human plasma viremia levels. These results suggest that DENV infection adds minimal cost to Ae. aegypti, an important finding when parameterizing the vector competence of this mosquito.

This study defined the genetic epidemiology of dengue viruses (DENV) in two pivotal phase III trials of the tetravalent dengue vaccine, CYD-TDV, and thereby enabled virus genotypespecific estimates of vaccine efficacy (VE). Envelope gene sequences (n = 661) from 11 DENV genotypes in 10 endemic countries provided a contemporaneous global snapshot of DENV population genetics and revealed high amino acid identity between the E genes of vaccine strains and wild-type viruses from trial participants, including at epitope sites targeted by virus neutralising human monoclonal antibodies. Post-hoc analysis of all CYD14/15 trial participants revealed a statistically significant genotype-level VE association within DENV-4, where efficacy was lowest against genotype I. In subgroup analysis of trial participants age 9-16 years, VE estimates appeared more balanced within each serotype, suggesting that genotype-level heterogeneity may be limited in older children. Post-licensure surveillance is needed to monitor vaccine performance against the backdrop of DENV sequence diversity and evolution.