Dengue virus-mosquito interactions

Dengue drug discovery: Progress, challenges and outlook

In the context of the only available vaccine (DENGVAXIA) that was marketed in several countries, but poses higher risks to unexposed individuals, the development of antivirals for dengue virus (DENV), whilst challenging, would bring significant benefits to public health. Here recent progress in the field of DENV drug discovery made in academic laboratories and industry is reviewed. Characteristics of an ideal DENV antiviral molecule, given the specific immunopathology provoked by this acute viral infection, are described. New chemical classes identified from biochemical, biophysical and phenotypic screens that target viral (especially NS4B) and host proteins, offer promising opportunities for further development. In particular, new methodologies ("omics") can accelerate the discovery of much awaited flavivirus specific inhibitors. Challenges and opportunities in lead identification activities as well as the path to clinical development of dengue drugs are discussed. To galvanize DENV drug discovery, collaborative public-public partnerships and open-access resources will greatly benefit both the DENV research community and DENV patients.

Periods of high dengue transmission defined by rainfall do not impact efficacy of dengue vaccine in regions of endemic disease

OBJECTIVE

To evaluate the association of rainy season with overall dengue disease incidence and with the efficacy of the Sanofi Pasteur recombinant, live, attenuated, tetravalent vaccine (CYD-TDV) in two randomized, controlled multicenter phase III clinical trials in Asia and Latin America.

METHODS

Rainy seasons were defined for each study site using climatological information from the World Meteorological Organization. The dengue attack rate in the placebo group for each study month was calculated as the number of symptomatic, virologically-confirmed dengue events in a given month divided by the number of participants at risk in the same month. Time-dependent Cox proportional hazard models were used to test whether rainy season was associated with dengue disease and whether it modified vaccine efficacy in each of the two trials and in both of the trials combined.

FINDINGS

Rainy season, country, and age were all significantly associated with dengue disease in both studies. Vaccine efficacy did not change during the rainy season in any of the analyses.

CONCLUSIONS

Although dengue transmission and exposure are expected to increase during the rainy season, our results indicate that CYD-TDV vaccine efficacy remains constant throughout the year in endemic regions.

The Multifaceted Roles of Autophagy in Flavivirus-Host Interactions

Autophagy is an evolutionarily conserved cellular process in which intracellular components are eliminated via lysosomal degradation to supply nutrients for organelle biogenesis and metabolic homeostasis. Flavivirus infections underlie multiple human diseases and thus exert an immense burden on public health worldwide. Mounting evidence indicates that host autophagy is subverted to modulate the life cycles of flaviviruses, such as hepatitis C virus, dengue virus, Japanese encephalitis virus, West Nile virus and Zika virus. The diverse interplay between autophagy and flavivirus infection not only regulates viral growth in host cells but also counteracts host stress responses induced by viral infection. In this review, we summarize the current knowledge on the role of autophagy in the flavivirus life cycle. We also discuss the impacts of virus-induced autophagy on the pathogeneses of flavivirus-associated diseases and the potential use of autophagy as a therapeutic target for curing flavivirus infections and related human diseases.

Using Multiple Scale Spatio-Temporal Patterns for Validating Spatially Explicit Agent-Based Models

Spatially explicit agent-based models (ABMs) have been widely utilized to simulate the dynamics of spatial processes that involve the interactions of individual agents. The assumptions embedded in the ABMs may be responsible for uncertainty in the model outcomes. To ensure the reliability of the outcomes in terms of their space-time patterns, model validation should be performed. In this paper, we propose the use of multiple scale spatio-temporal patterns for validating spatially explicit ABMs. We evaluated several specifications of vector-borne disease transmission models by comparing space-time patterns of model outcomes to observations at multiple scales via the sum of root mean square error (RMSE) measurement. The results indicate that specifications of the spatial configurations of residential area and immunity status of individual humans are of importance to reproduce observed patterns of dengue outbreaks at multiple space-time scales. Our approach to using multiple scale spatio-temporal patterns can help not only to understand the dynamic associations between model specifications and model outcomes, but also to validate spatially explicit ABMs.

Immunoinformatics and molecular docking studies reveal potential epitope-based peptide vaccine against DENV-NS3 protein

Dengue, still a "Neglected Tropical Disease" is somehow injustice and remains uncontrolled globally. World Health Organization (2012-2020) reported that the world's half population is living in dengue-affected regions. Therefore, effective drug candidates or promising vaccines are urgently needed to control the dengue. It is an acute febrile disease caused by mosquito borne dengue viruses (DENVs) which belong to the genus Flavivirus with four serotypes. In present work, immunoinformatics approach was utilized to predict the antigenic epitopes of dengue proteins for the development of DENV vaccine. B-cell and cytotoxic T-lymphocyte epitopes were predicted for NS3 dengue protein. Docking complexes of 17 antigenic B-cell epitopes of various lengths and 4 CTL epitopes with antigenic sites were investigated followed by binding interaction analyses of top predicted peptides with MHC-I HLA-A2 molecule. These predicted epitopes with antigenic amino acids might present a preliminary set of peptides for future vaccine development against DENV.

Scoping review on vector-borne diseases in urban areas: transmission dynamics, vectorial capacity and co-infection

BACKGROUND

Transmission dynamics, vectorial capacity, and co-infections have substantial impacts on vector-borne diseases (VBDs) affecting urban and suburban populations. Reviewing key factors can provide insight into priority research areas and offer suggestions for potential interventions.

MAIN BODY

Through a scoping review, we identify knowledge gaps on transmission dynamics, vectorial capacity, and co-infections regarding VBDs in urban areas. Peer-reviewed and grey literature published between 2000 and 2016 was searched. We screened abstracts and full texts to select studies. Using an extraction grid, we retrieved general data, results, lessons learned and recommendations, future research avenues, and practice implications. We classified studies by VBD and country/continent and identified relevant knowledge gaps. Of 773 articles selected for full-text screening, 50 were included in the review: 23 based on research in the Americas, 15 in Asia, 10 in Africa, and one each in Europe and Australia. The largest body of evidence concerning VBD epidemiology in urban areas concerned dengue and malaria. Other arboviruses covered included chikungunya and West Nile virus, other parasitic diseases such as leishmaniasis and trypanosomiasis, and bacterial rickettsiosis and plague. Most articles retrieved in our review combined transmission dynamics and vectorial capacity; only two combined transmission dynamics and co-infection. The review identified significant knowledge gaps on the role of asymptomatic individuals, the effects of co-infection and other host factors, and the impacts of climatic, environmental, and socioeconomic factors on VBD transmission in urban areas. Limitations included the trade-off from narrowing the search strategy (missing out on classical modelling studies), a lack of studies on co-infections, most studies being only descriptive, and few offering concrete public health recommendations. More research is needed on transmission risk in homes and workplaces, given increasingly dynamic and mobile populations. The lack of studies on co-infection hampers monitoring of infections transmitted by the same vector.

CONCLUSIONS

Strengthening VBD surveillance and control, particularly in asymptomatic cases and mobile populations, as well as using early warning tools to predict increasing transmission, were key strategies identified for public health policy and practice.

Dengue fever. Clinical features of 567 consecutive patients admitted to a tertiary care center in Saudi Arabia

OBJECTIVES

To delineate the clinical features and outcomes of dengue infection and to guide clinician of early diagnosis and identification of risks factors for dengue hemorrhagic fever. Methods: This study is a retrospective cross-sectional. Clinical records of 567 patients with a confirmed diagnosis of dengue infection, admitted to a single hospital in Jeddah, Saudi Arabia, between January 2010 and  June 2014 were reviewed.  Results: Dengue infection was most common in adult males. Sixty-eight percent of infections were in Saudi nationals. In addition to the diagnostic clinical features, leucopenia and thrombocytopenia were typical of dengue infection. Approximately 4.1% of adult patients and 7.1% of pediatric patients developed dengue hemorrhagic fever (DHF). Abdominal pain and vomiting were more common in patients developing DHF. Mean platelet count was lower in adult, but not pediatric patients developing DHF. Peak alanine aminotransferase (ALT) was higher in adult and pediatric patients developing DHF. Three patients died, 2 of them developed DHF. Ninety-eight percent of adult patients and 92% of pediatric patients made a full recovery. Conclusions:   Dengue infection is common in Jeddah.  Abdominal pain and vomiting, thrombocytopenia, and elevated ALT are typical of severe infection, which is more likely to be associated with significant morbidity and mortality.

Climate variability and dengue hemorrhagic fever in Southeast Sulawesi Province, Indonesia

To determine the association of climatic factors and dengue hemorrhagic fever and to develop the prediction approach of future dengue transmission. The study used totally monthly dengue hemorrhagic fever cases at Health Office Kendari, Southeast Sulawesi, Indonesia. Monthly meteorological data, consisting of temperature, rainfall, and humidity, was obtained from the Meteorology, Climatology and Geophysics Agency in Kendari district. All data analysis, including Spearman and Poisson distribution, was carried out in R Studio (version 3.3.2) utilizing the R statistical language version 2.15. The highest rate of dengue hemorrhagic fever cases was found in January, February, and March. Temperature averages at lag 2 (p = 0.53, p < 0.0001), lag 3 (p = 0.59, p < 0.0001), and lag 4 (p = 0.41, p < 0.01)) correlated with the incident rate of DHF. The average temperature at lag 2 was found to have a positive impact on the incidence of DHF by Poisson function. This study provides preliminary evidence of the influence of climatic factors on dengue transmission.

ENSO-driven climate variability promotes periodic major outbreaks of dengue in Venezuela

Dengue is a mosquito-borne viral disease of global impact. In Venezuela, dengue has emerged as one of the most important public health problems of urban areas with frequent epidemics since 2001. The long-term pattern of this disease has involved not only a general upward trend in cases but also a dramatic increase in the size and frequency of epidemic outbreaks. By assuming that climate variability has a relevant influence on these changes in time, we quantified the periodicity of dengue incidence in time-series of data from two northern regions of Venezuela. Disease cycles of 1 and 3-4 years (p < 0.05) were detected. We determined that dengue cycles corresponded with local climate and the El Niño Southern Oscillation (ENSO) variation at both seasonal and inter-annual scales (every 2-3 years). Dengue incidence peaks were more prevalent during the warmer and dryer years of El Niño confirming that ENSO is a regional climatic driver of such long-term periodicity through local changes in temperature and rainfall. Our findings support the evidence of the effect of climate on dengue dynamics and advocate the incorporation of climate information in the surveillance and prediction of this arboviral disease in Venezuela.

Dengue Virus and Its Inhibitors: A Brief Review

The global occurrence of viral infectious diseases poses a significant threat to human health. Dengue virus (DENV) infection is one of the most noteworthy of these infections. According to a WHO survey, approximately 400 million people are infected annually; symptoms deteriorate in approximately one percent of cases. Numerous foundational and clinical investigations on viral epidemiology, structure and function analysis, infection source and route, therapeutic targets, vaccines, and therapeutic drugs have been conducted by both academic and industrial researchers. At present, CYD-TDV or Dengvaxia^® is the only approved vaccine, but potent inhibitors are currently under development. In this review, an overview of the viral life circle and the history of DENVs is presented, and the most recently reported antiviral candidates and newly discovered promising targets are focused and summarized. We believe that these successes and failures have enabled progress in anti-DENV drug discovery and hope that our review will stimulate further innovation in this area.

Dynamics of dengue disease with human and vector mobility

Dengue is a vector borne disease transmitted to humans by Aedes aegypti mosquitoes carrying virus of different serotypes. Dengue exhibits complex spatial and temporal dynamics, influenced by various biological, human and environmental factors. In this work, we study the dengue spread for a single serotype (DENV-1) including statistical models of human mobility with exponential step length distribution, by using reaction-diffusion equations and Stochastic Cellular Automata (SCA) approach. We analyze the spatial and temporal spreading of the disease using parameters from field studies. We choose mosquito density data from Ahmedabad city as a proxy for climate data in our SCA model. We find an interesting result that although human mobility makes the infection spread faster, there is an apparent early suppression of the epidemic compared to immobile humans. The disease extinction time is lesser when human mobility is included.

The non-canonical Notch signaling is essential for the control of fertility in Aedes aegypti

The Notch signaling pathway is a highly evolutionarily-conserved cell-cell signaling pathway that regulates many events during development. It plays a pivotal role in the regulation of fundamental cellular processes, such as cell proliferation, stem cell maintenance, and differentiation during embryonic and adult development. However, functions of Notch signaling in Aedes aegypti, the major mosquito vector for dengue, are largely unknown. In this study, we identified a unique feature of A. aegypti Notch (AaNotch) in the control of the sterile-like phenotype in female mosquitoes. Silencing AaNotch with a reverse genetic approach significantly reduced the fecundity and fertility of the mosquito. Silencing AaNotch also resulted in the prevention of micropyle formation, which led to impaired fertilization. In addition, JNK phosphorylation (a signaling molecule in the non-canonical Notch signaling pathway) was inhibited in the absence of AaNotch. Furthermore, treatment with a JNK inhibitor in the mosquito resulted in impaired fecundity and fertility. Taken together, our results demonstrate that non-canonical Notch signaling is essential for controlling fertility in the A. aegypti mosquito.

The spatial and temporal scales of local dengue virus transmission in natural settings: a retrospective analysis

Background

Dengue is a vector-borne disease caused by the dengue virus (DENV). Despite the crucial role of Aedes mosquitoes in DENV transmission, pure vector indices poorly correlate with human infections. Therefore there is great need for a better understanding of the spatial and temporal scales of DENV transmission between mosquitoes and humans. Here, we have systematically monitored the circulation of DENV in individual Aedes spp. mosquitoes and human patients from Caratinga, a dengue endemic city in the state of Minas Gerais, in Southeast Brazil. From these data, we have developed a novel stochastic point process pattern algorithm to identify the spatial and temporal association between DENV infected mosquitoes and human patients.

Methods

The algorithm comprises of: (i) parameterization of the variogram for the incidence of each DENV serotype in mosquitoes; (ii) identification of the spatial and temporal ranges and variances of DENV incidence in mosquitoes in the proximity of humans infected with dengue; and (iii) analysis of the association between a set of environmental variables and DENV incidence in mosquitoes in the proximity of humans infected with dengue using a spatio-temporal additive, geostatistical linear model.

Results

DENV serotypes 1 and 3 were the most common virus serotypes detected in both mosquitoes and humans. Using the data on each virus serotype separately, our spatio-temporal analyses indicated that infected humans were located in areas with the highest DENV incidence in mosquitoes, when incidence is calculated within 2.5–3 km and 50 days (credible interval 30–70 days) before onset of symptoms in humans. These measurements are in agreement with expected distances covered by mosquitoes and humans and the time for virus incubation. Finally, DENV incidence in mosquitoes found in the vicinity of infected humans correlated well with the low wind speed, higher air temperature and northerly winds that were more likely to favor vector survival and dispersal in Caratinga.

Conclusions

We have proposed a new way of modeling bivariate point pattern on the transmission of arthropod-borne pathogens between vector and host when the location of infection in the latter is known. This strategy avoids some of the strong and unrealistic assumptions made by other point-process models. Regarding virus transmission in Caratinga, our model showed a strong and significant association between high DENV incidence in mosquitoes and the onset of symptoms in humans at specific spatial and temporal windows. Together, our results indicate that vector surveillance must be a priority for dengue control. Nevertheless, localized vector control at distances lower than 2.5 km around premises with infected vectors in densely populated areas are not likely to be effective.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2662-6) contains supplementary material, which is available to authorized users.

Patterns of Urban Housing Shape Dengue Distribution in Singapore at Neighborhood and Country Scales

Dengue is the most important human arboviral disease in Singapore. We classified residential areas into low-rise and high-rise housing and investigated the influence of urban drainage on the distribution of dengue incidence and outdoor breeding at neighborhood and country scales. In Geylang area (August 2014 to August 2015), dengue incidence was higher in a subarea of low-rise housing compared to high-rise one, averaging 26.7 (standard error, SE = 4.83) versus 2.43 (SE = 0.67) per 1,000 people. Outdoor breeding drains of Aedes aegypti have clustered in the low-rise housing subarea. The pupal density per population was higher in the low-rise blocks versus high-rise ones, 246 (SE = 69.08) and 35.4 (SE = 25.49) per 1,000 people, respectively. The density of urban drainage network in the low-rise blocks is double that in the high-rise ones, averaging 0.05 (SE = 0.0032) versus 0.025 (SE = 0.00245) per meter. Further, a holistic analysis at a country-scale has confirmed the role of urban hydrology in shaping dengue distribution in Singapore. Dengue incidence (2013-2015) is proportional to the fractions of the area (or population) of low-rise housing. The drainage density in low-rise housing is 4 times that corresponding estimate in high-rise areas, 2.59 and 0.68 per meter, respectively. Public housing in agglomerations of high-rise buildings could have a positive impact on dengue if this urban planning comes at the expense of low-rise housing. City planners in endemic regions should consider the density of drainage networks for both the prevention of flooding and the breeding of mosquitoes.

Using paired serology and surveillance data to quantify dengue transmission and control during a large outbreak in Fiji

Dengue is a major health burden, but it can be challenging to examine transmission and evaluate control measures because outbreaks depend on multiple factors, including human population structure, prior immunity and climate. We combined population-representative paired sera collected before and after the 2013/14 dengue-3 outbreak in Fiji with surveillance data to determine how such factors influence transmission and control in island settings. Our results suggested the 10-19 year-old age group had the highest risk of infection, but we did not find strong evidence that other demographic or environmental risk factors were linked to seroconversion. A mathematical model jointly fitted to surveillance and serological data suggested that herd immunity and seasonally varying transmission could not explain observed dynamics. However, the model showed evidence of an additional reduction in transmission coinciding with a vector clean-up campaign, which may have contributed to the decline in cases in the later stages of the outbreak.

Germline Cas9 expression yields highly efficient genome engineering in a major worldwide disease vector, Aedes aegypti

The development of CRISPR/Cas9 technologies has dramatically increased the accessibility and efficiency of genome editing in many organisms. In general, in vivo germline expression of Cas9 results in substantially higher activity than embryonic injection. However, no transgenic lines expressing Cas9 have been developed for the major mosquito disease vector Aedes aegypti Here, we describe the generation of multiple stable, transgenic Ae. aegypti strains expressing Cas9 in the germline, resulting in dramatic improvements in both the consistency and efficiency of genome modifications using CRISPR. Using these strains, we disrupted numerous genes important for normal morphological development, and even generated triple mutants from a single injection. We have also managed to increase the rates of homology-directed repair by more than an order of magnitude. Given the exceptional mutagenic efficiency and specificity of the Cas9 strains we engineered, they can be used for high-throughput reverse genetic screens to help functionally annotate the Ae. aegypti genome. Additionally, these strains represent a step toward the development of novel population control technologies targeting Ae. aegypti that rely on Cas9-based gene drives.

Inhibition of dengue virus replication by novel inhibitors of RNA-dependent RNA polymerase and protease activities

Dengue virus (DENV) is the leading mosquito-transmitted viral infection in the world. With more than 390 million new infections annually, and up to 1 million clinical cases with severe disease manifestations, there continues to be a need to develop new antiviral agents against dengue infection. In addition, there is no approved anti-DENV agents for treating DENV-infected patients. In the present study, we identified new compounds with anti-DENV replication activity by targeting viral replication enzymes - NS5, RNA-dependent RNA polymerase (RdRp) and NS3 protease, using cell-based reporter assay. Subsequently, we performed an enzyme-based assay to clarify the action of these compounds against DENV RdRp or NS3 protease activity. Moreover, these compounds exhibited anti-DENV activity in vivo in the ICR-suckling DENV-infected mouse model. Combination drug treatment exhibited a synergistic inhibition of DENV replication. These results describe novel prototypical small anti-DENV molecules for further development through compound modification and provide potential antivirals for treating DENV infection and DENV-related diseases.

The impact of temperature and Wolbachia infection on vector competence of potential dengue vectors Aedes aegypti and Aedes albopictus in the transmission of dengue virus serotype 1 in southern Taiwan

BACKGROUND

We evaluated the impact of temperature and Wolbachia infection on vector competence of the local Aedes aegypti and Ae. albopictus populations of southern Taiwan in the laboratory.

RESULTS

After oral infection with dengue serotype 1 virus (DENV-1), female mosquitoes were incubated at temperatures of 10, 16, 22, 28 and 34 °C. Subsequently, salivary gland, head, and thorax-abdomen samples were analyzed for their virus titer at 0, 5, 10, 15, 20, 25 and 30 days post-infection (dpi) by real-time RT-PCR. The results showed that Ae. aegypti survived significantly longer and that dengue viral genome levels in the thorax-abdomen (10^{3.25 ± 0.53}-10^{4.09 ± 0.71} PFU equivalents/ml) and salivary gland samples (10^{2.67 ± 0.33}-10^{3.89 ± 0.58} PFU equivalents/ml) were significantly higher at high temperature (28-34 °C). The survival of Ae. albopictus was significantly better at 16 or 28 °C, but the virus titers from thorax-abdomen (10^0.70-10^{2.39 ± 1.31} PFU equivalents/ml) and salivary gland samples (10^{0.12 ± 0.05}-10^{1.51 ± 0.31} PFU equivalents/ml) were significantly higher at 22-28 °C. Within viable temperature ranges, the viruses were detectable after 10 dpi in salivary glands and head tissues in Ae. aegypti and after 5-10 dpi in Ae. albopictus. Vector competence was measured in Ae. albopictus with and without Wolbachia at 28 °C. Wolbachia-infected mosquitoes survived significantly better and carried lower virus titers than Wolbachia-free mosquitoes. Wolbachia coinfections (92.8-97.2%) with wAlbA and wAlbB strains were commonly found in a wild population of Ae. albopictus.

CONCLUSIONS

In southern Taiwan, Ae. aegypti is the main vector of dengue and Ae. albopictus has a non-significant role in the transmission of dengue virus due to the high prevalence of Wolbachia infection in the local mosquito population of southern Taiwan.

ANTIVIRAL ACTIVITY OF COPPER(II)CHLORIDE DIHYDRATE AGAINST DENGUE VIRUS TYPE-2 IN VERO CELL

Infection of dengue virus (DENV) was number of globally significant emerging pathogen. Antiviral dengue therapies ar importantly needed to control emerging dengue. Dengue virus (DENV) is mosquito-borne arboviruses responsible for causing acute systemic diseases and grievous health conditions in humans. To date, there is no clinically approved dengue vaccine or antiviral for humans, even though there have been great efforts towards this end. Copper and copper compounds have more effective in inactivation viruses, likes an influenza virus and human immunodeficiency virus (HIV). Purpose in this project was investigated of Copper(II)chloride Dihydrate antiviral compound were further tested for inhibitory effect on the replication of DENV-2 in cell culture. DENV replication was measures by Enzyme linked Immunosorbent Assay (ELISA) with selectivity index value (SI) was determined as the ratio of cytotoxic concentration 50 (CC50) to inhibitory concentration 50 (IC50) for compound. The maximal inhibitory concentration (IC50) of Copper(II)chloride Dihydrate against dengue virus type-2 was 0.13 μg/ml. The cytotoxic concentration (CC50) of compound against Vero cell was 5.03 μg/ml. The SI values for Copper(II)chloride Dihydrate 38.69. Result of this study suggest that Copper(II)chloride Dihydrate demonstated significant anti-DENV-2 inhibitory activities and not toxic in the Vero cells. Copper mechanisms play an important role in the prevention of copper toxicity, exposure to excessive levels of copper can result in a number of adverse health effects, as a result increased reactive oxygen species and oxidative damage to lipid, DNA, and proteins have been observed in human cell culture models or clinical syndromes of severe copper deficiency and inhibition was attributed to released cupric ions which react with cysteine residues on the surface of the protease.

Multiple introductions of the dengue vector, Aedes aegypti, into California

The yellow fever mosquito Aedes aegypti inhabits much of the tropical and subtropical world and is a primary vector of dengue, Zika, and chikungunya viruses. Breeding populations of A. aegypti were first reported in California (CA) in 2013. Initial genetic analyses using 12 microsatellites on collections from Northern CA in 2013 indicated the South Central US region as the likely source of the introduction. We expanded genetic analyses of CA A. aegypti by: (a) examining additional Northern CA samples and including samples from Southern CA, (b) including more southern US populations for comparison, and (c) genotyping a subset of samples at 15,698 SNPs. Major results are: (1) Northern and Southern CA populations are distinct. (2) Northern populations are more genetically diverse than Southern CA populations. (3) Northern and Southern CA groups were likely founded by two independent introductions which came from the South Central US and Southwest US/northern Mexico regions respectively. (4) Our genetic data suggest that the founding events giving rise to the Northern CA and Southern CA populations likely occurred before the populations were first recognized in 2013 and 2014, respectively. (5) A Northern CA population analyzed at multiple time-points (two years apart) is genetically stable, consistent with permanent in situ breeding. These results expand previous work on the origin of California A. aegypti with the novel finding that this species entered California on multiple occasions, likely some years before its initial detection. This work has implications for mosquito surveillance and vector control activities not only in California but also in other regions where the distribution of this invasive mosquito is expanding.

Infectious diseases transmitted by Aedes aegypti, also known as the yellow fever mosquito, are of growing concern in tropical and subtropical regions. Dengue and Zika incidences are increasing, and no vaccines are currently available. Here we investigate the origin of California A. aegypti and find that this mosquito likely entered California on multiple occasions, at least once from the South Central US region and once from the Southwest US/northern MX region. The evidence suggests that the first invasion event likely occurred some years before its initial detection in 2013, despite California’s extensive and active surveillance program, implying that this invasive mosquito can go undetected. Understanding the invasion dynamics, gene flow, and population structure of A. aegypti can improve the monitoring of mosquitoes and prevent outbreaks of vector-borne disease.

Cell fusing agent virus and dengue virus mutually interact in Aedes aegypti cell lines

The genus Flavivirus contains more than 70 single-stranded, positive-sense arthropod-borne RNA viruses. Some flaviviruses are particularly medically important to humans and other vertebrates including dengue virus (DENV), West Nile virus, and yellow fever virus. These viruses are transmitted to vertebrates by mosquitoes and other arthropod species. Mosquitoes are also infected by insect-specific flaviviruses (ISFs) that do not appear to be infective to vertebrates. Cell fusing agent virus (CFAV) was the first described ISF, which was discovered in an Aedes aegypti cell culture. We found that while CFAV infection could be significantly reduced by application of RNAi against the NS5 gene, removal of the treatment led to quick restoration of CFAV replication. Interestingly, we found that CFAV infection significantly enhanced replication of DENV, and vice versa, DENV infection significantly enhanced replication of CFAV in mosquito cells. We have shown that CFAV infection leads to increase in the expression of ribonuclease kappa (RNASEK), which is known to promote infection of viruses that rely on endocytosis and pH-dependent entry. Knockdown of RNASEK by dsRNA resulted in reduced DENV replication. Thus, increased expression of RNASEK induced by CFAV is likely to contribute to enhanced DENV replication in CFAV-infected cells.

Dengue subgenomic flaviviral RNA disrupts immunity in mosquito salivary glands to increase virus transmission

Globally re-emerging dengue viruses are transmitted from human-to-human by Aedes mosquitoes. While viral determinants of human pathogenicity have been defined, there is a lack of knowledge of how dengue viruses influence mosquito transmission. Identification of viral determinants of transmission can help identify isolates with high epidemiological potential. Additionally, mechanistic understanding of transmission will lead to better understanding of how dengue viruses harness evolution to cycle between the two hosts. Here, we identified viral determinants of transmission and characterized mechanisms that enhance production of infectious saliva by inhibiting immunity specifically in salivary glands. Combining oral infection of Aedes aegypti mosquitoes and reverse genetics, we identified two 3’ UTR substitutions in epidemic isolates that increased subgenomic flaviviral RNA (sfRNA) quantity, infectious particles in salivary glands and infection rate of saliva, which represents a measure of transmission. We also demonstrated that various 3’UTR modifications similarly affect sfRNA quantity in both whole mosquitoes and human cells, suggesting a shared determinism of sfRNA quantity. Furthermore, higher relative quantity of sfRNA in salivary glands compared to midgut and carcass pointed to sfRNA function in salivary glands. We showed that the Toll innate immune response was preferentially inhibited in salivary glands by viruses with the 3’UTR substitutions associated to high epidemiological fitness and high sfRNA quantity, pointing to a mechanism for higher saliva infection rate. By determining that sfRNA is an immune suppressor in a tissue relevant to mosquito transmission, we propose that 3’UTR/sfRNA sequence evolution shapes dengue epidemiology not only by influencing human pathogenicity but also by increasing mosquito transmission, thereby revealing a viral determinant of epidemiological fitness that is shared between the two hosts.

Dengue is a re-emerging global disease transmitted from human-to-human by mosquitoes. While environmental and host immune factors are important, viral determinants of mosquito transmission also shape the epidemiology of dengue. Understanding how dengue viruses influence transmission will help identify isolates with high epidemic potential and untangle the evolutionary pressures at play in the dual-host cycle. Here, we identified 2 substitutions in the 3’UTR of epidemic isolates that increase transmission through immune suppression in the salivary glands. Using oral infection of Aedes aegypti mosquitoes, we reported that epidemic isolates produced more subgenomic flaviviral RNA (sfRNA) in salivary glands. SfRNA is generated from the 3’UTR sequence remaining after partial genome degradation by a host nuclease. Using reverse genetics, we identified the two 3’UTR substitutions responsible for the higher sfRNA quantity in salivary glands. We further showed that these substitutions increased dengue virus titer in salivary glands and rate of saliva infection, and suppressed the Toll immune response in salivary glands. Our study identifies the substitutions that determine virus epidemiological fitness and provides a mechanism for sfRNA-mediated enhancement of transmission. Together with previous work demonstrating that sfRNA sequence modification influences dengue virus pathogenicity in human, and that shows variation in sfRNA sequence when the viruses transition from one host to vector and vice versa, our study supports that sfRNA evolution is constrained in the two hosts.

The Influence of Spatial Configuration of Residential Area and Vector Populations on Dengue Incidence Patterns in an Individual-Level Transmission Model

Dengue is a mosquito-borne infectious disease that is endemic in tropical and subtropical countries. Many individual-level simulation models have been developed to test hypotheses about dengue virus transmission. Often these efforts assume that human host and mosquito vector populations are randomly or uniformly distributed in the environment. Although, the movement of mosquitoes is affected by spatial configuration of buildings and mosquito populations are highly clustered in key buildings, little research has focused on the influence of the local built environment in dengue transmission models. We developed an agent-based model of dengue transmission in a village setting to test the importance of using realistic environments in individual-level models of dengue transmission. The results from one-way ANOVA analysis of simulations indicated that the differences between scenarios in terms of infection rates as well as serotype-specific dominance are statistically significant. Specifically, the infection rates in scenarios of a realistic environment are more variable than those of a synthetic spatial configuration. With respect to dengue serotype-specific cases, we found that a single dengue serotype is more often dominant in realistic environments than in synthetic environments. An agent-based approach allows a fine-scaled analysis of simulated dengue incidence patterns. The results provide a better understanding of the influence of spatial heterogeneity on dengue transmission at a local scale.

Ecological Niche Model for Predicting Distribution of Disease-Vector Mosquitoes in Yucatán State, México

The majority of the Yucatán State, México, presents subtropical climate that is suitable for many species of mosquitoes that are known to be vectors of diseases, including those from the genera Aedes and Culex. The objective of this study is to identify the geographic distribution of five species from these two genera and estimate the human population at risk of coming in contact with them. We compiled distributional data for Aedes aegypti (L.), Aedes (Howardina) cozumelensis (Diaz Najera), Culex coronator Dyar and Knab, Culex quinquefasciatus Say, and Culex thriambus Dyar from several entomological studies in Yucatán between March 2010 and September 2014. Based on these data, we constructed ecological niche models to predict the spatial distribution of each species using the MaxEnt algorithm. Our models identified areas with suitable environments for Ae. aegypti in most of Yucatán. A similar percentage of urban (97.1%) and rural (96.5%) populations were contained in areas of highest suitability for Ae. aegypti, and no spatial pattern was found (Moran's I = 0.33, P = 0.38); however, we found an association of abundance of immature forms of this species with annual mean temperature (r = 0.19, P ≤ 0.001) and annual precipitation (r = 0.21, P ≤ 0.001). Aedes cozumelensis is also distributed in most areas of the Yucatán State; Cx. quinquefasciatus, Cx. coronator, and Cx. thriambus are restricted to the northwest. The information generated in this study can inform decision-making to address control measures in priority areas with presence of these vectors.

Adult-onset, chronic, cyclic thrombocytopenia in a Rhesus macaque (Macaca mulatta) after dengue virus vaccination and viral challenge

An 8-year-old, male Rhesus macaque (Macaca mulatta), previously used for dengue virus (DENV) vaccine research with viral challenge, was presented with adult-onset, chronic, cyclic thrombocytopenia. Platelet number, morphology, and function were evaluated by automated hematology, peripheral blood smears, electron microscopy, flow cytometry, and impedance aggregometry. Bone marrow was evaluated by cytology. Both serum anti-dengue nonstructural protein 1 (NS1) antibodies and anti-platelet antibodies were detected by ELISA. Platelet characterization showed a lack of aggregation to all agonists (ADP, ASP, and collagen), increased activation with increased expression of surface marker (HLA-ABC), and an absence of surface receptor GPIX during clinical episodes of petechiae and ecchymoses, even in the presence of normal platelet counts. Bone marrow aspirates identified potential mild megakaryocytic hypoplasia. All platelet functions and morphologic attributes were within normal limits during clinically normal phases. Presence of anti-dengue NS1 serum antibodies confirmed a positive DENV titer 8 years postvaccination. Based on the history and clinical findings, a primary differential diagnosis for this chronic, cyclic platelet pathology was autoimmune platelet destruction with potential bone marrow involvement.

Role of Mast Cells in Dengue Virus Pathogenesis

Dengue is currently regarded as the most common arthropod-borne viral disease in tropical and subtropical areas, with an estimated 50-100 million infections occurring each year. Nearly all patients experience a self-limiting clinical course; however, the illness ranges from undifferentiated fever to severe hemorrhagic fever with or without shock syndrome complications. There are several immune cells associated with the pathogenesis of dengue virus (DENV) infection and systemic spread, including dendritic cells, macrophages, and mast cells (MCs). MCs are widely recognized for their immune functions and as cellular regulators of vascular integrity in human skin. Furthermore, these cells are able to detect DENV, which results in activation and degranulation of potent vasoactive mediators prestored in the granules. These mediators can act directly on vascular endothelium, increasing permeability and inducing vascular leakage. This review is designed to present an insight into the role of MCs during DENV infection and the dual functions in immune protection and contribution to the most severe forms of dengue.

Joint effects of climate variability and socioecological factors on dengue transmission: epidemiological evidence

OBJECTIVE

To assess the epidemiological evidence on the joint effects of climate variability and socioecological factors on dengue transmission.

METHODS

Following PRISMA guidelines, a detailed literature search was conducted in PubMed, Web of Science and Scopus. Peer-reviewed, freely available and full-text articles, considering both climate and socioecological factors in relation to dengue, published in English from January 1993 to October 2015 were included in this review.

RESULTS

Twenty studies have met the inclusion criteria and assessed the impact of both climatic and socioecological factors on dengue dynamics. Among those, four studies have further investigated the relative importance of climate variability and socioecological factors on dengue transmission. A few studies also developed predictive models including both climatic and socioecological factors.

CONCLUSIONS

Due to insufficient data, methodological issues and contextual variability of the studies, it is hard to draw conclusion on the joint effects of climate variability and socioecological factors on dengue transmission. Future research should take into account socioecological factors in combination with climate variables for a better understanding of the complex nature of dengue transmission as well as for improving the predictive capability of dengue forecasting models, to develop effective and reliable early warning systems.

Modification of S-Adenosyl-l-Homocysteine as Inhibitor of Nonstructural Protein 5 Methyltransferase Dengue Virus Through Molecular Docking and Molecular Dynamics Simulation

Dengue fever is still a major threat worldwide, approximately threatening two-fifths of the world's population in tropical and subtropical countries. Nonstructural protein 5 (NS5) methyltransferase enzyme plays a vital role in the process of messenger RNA capping of dengue by transferring methyl groups from S-adenosyl-l-methionine to N7 atom of the guanine bases of RNA and the RNA ribose group of 2'OH, resulting in S-adenosyl-l-homocysteine (SAH). The modification of SAH compound was screened using molecular docking and molecular dynamics simulation, along with computational ADME-Tox (absorption, distribution, metabolism, excretion, and toxicity) test. The 2 simulations were performed using Molecular Operating Environment (MOE) 2008.10 software, whereas the ADME-Tox test was performed using various software. The modification of SAH compound was done using several functional groups that possess different polarities and properties, resulting in 3460 ligands to be docked. After conducting docking simulation, we earned 3 best ligands (SAH-M331, SAH-M2696, and SAH-M1356) based on ΔG_binding and molecular interactions, which show better results than the standard ligands. Moreover, the results of molecular dynamics simulation show that the best ligands are still able to maintain the active site residue interaction with the binding site until the end of the simulation. After a series of molecular docking and molecular dynamics simulation were performed, we concluded that SAH-M1356 ligand is the most potential SAH-based compound to inhibit NS5 methyltransferase enzyme for treating dengue fever.

Protocols for Investigating the Host-tissue Distribution, Transmission-mode, and Effect on the Host Fitness of a Densovirus in the Cotton Bollworm

Many novel viruses have been discovered in animal hosts using next-generation sequencing technologies. Previously, we reported a mutualistic virus, Helicoverpa armigera densovirus (HaDV2), in a lepidopteran species, the cotton bollworm, Helicoverpa armigera (Hubner). Here, we describe the protocols that are currently used to study the effect of HaDV2 on its host. First, we establish a HaDV2-free cotton bollworm colony from a single breeding pair. Then, we orally inoculate some neonate larval offspring with HaDV2-containing filtered liquid to produce two colonies with the same genetic background: one HaDV2-infected, the other uninfected. A protocol to compare life table parameters (e.g., larval, pupal, and adult periods and fecundity) between the HaDV2-infected and -uninfected individuals is also presented, as are the protocols for determining the host-tissue distribution and transmission efficiency of HaDV2. These protocols would also be suitable for investigating the effects of other orally transmitted viruses on their insect hosts, lepidopteran hosts in particular.

Estimation of reproduction number and non stationary spectral analysis of dengue epidemic

In this work we analyze the post monsoon Dengue outbreaks by analyzing the transient and long term dynamics of Dengue incidences and its environmental correlates in Ahmedabad city in western India from 2005 to 2012. We calculate the reproduction number R_p using the growth rate of post monsoon Dengue outbreaks and biological parameters like host and vector incubation periods and vector mortality rate, and its uncertainties are estimated through Monte-Carlo simulations by sampling parameters from their respective probability distributions. Reduction in Female Aedes mosquito density required for an effective prevention of Dengue outbreaks is also calculated. The non stationary pattern of Dengue incidences and its climatic correlates like rainfall temperature is analyzed through Wavelet based methods. We find that the mean time lag between peak of monsoon and Dengue is 9 weeks. Monsoon and Dengue cases are phase locked from 2008 to 2012 in the 16 to maintain consistency make it "16 to 32" 32 weeks band. The duration of post monsoon outbreak has been increasing every year, especially post 2008, even though the intensity and duration of monsoon has been decreasing. Temperature and Dengue incidences show correlations in the same band, but phase lock is not stationary.

A new paradigm for Aedes spp. surveillance using gravid ovipositing sticky trap and NS1 antigen test kit

Background

Dengue remains a serious public health problem in Southeast Asia and has increased 37-fold in Malaysia compared to decades ago. New strategies are urgently needed for early detection and control of dengue epidemics.

Methods

We conducted a two year study in a high human density dengue-endemic urban area in Selangor, where Gravid Ovipositing Sticky (GOS) traps were set up to capture adult Aedes spp. mosquitoes. All Aedes mosquitoes were tested using the NS1 dengue antigen test kit. All dengue cases from the study site notified to the State Health Department were recorded. Weekly microclimatic temperature, relative humidity (RH) and rainfall were monitored.

Results

Aedes aegypti was the predominant mosquito (95.6%) caught in GOS traps and 23% (43/187 pools of 5 mosquitoes each) were found to be positive for dengue using the NS1 antigen kit. Confirmed cases of dengue were observed with a lag of one week after positive Ae. aegypti were detected. Aedes aegypti density as analysed by distributed lag non-linear models, will increase lag of 2–3 weeks for temperature increase from 28 to 30 °C; and lag of three weeks for increased rainfall.

Conclusion

Proactive strategy is needed for dengue vector surveillance programme. One method would be to use the GOS trap which is simple to setup, cost effective (below USD 1 per trap) and environmental friendly (i.e. use recyclable plastic materials) to capture Ae. aegypti followed by a rapid method of detecting of dengue virus using the NS1 dengue antigen kit. Control measures should be initiated when positive mosquitoes are detected.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2091-y) contains supplementary material, which is available to authorized users.

Seasonal patterns of dengue fever and associated climate factors in 4 provinces in Vietnam from 1994 to 2013

BACKGROUND

In Vietnam, dengue fever (DF) is still a leading cause of hospitalization. The main objective of this study was to evaluate the seasonality and association with climate factors (temperature and precipitation) on the incidences of DF in four provinces where the highest incidence rates were observed from 1994 to 2013 in Vietnam.

METHODS

Incidence rates (per 100,000) were calculated on a monthly basis from during the study period. The seasonal-decomposition procedure based on loess (STL) was used in order to assess the trend and seasonality of DF. In addition, a seasonal cycle subseries (SCS) plot and univariate negative binomial regression (NBR) model were used to evaluate the monthly variability with statistical analysis. Lastly, a generalized estimating equation (GEE) was used to assess the relationship between monthly incidence rates and weather factors (temperature and precipitation).

RESULTS

We found that increased incidence rates were observed in the second half of each year (from May through December) which is the rainy season in each province. In Hanoi, the final model showed that 1 °C rise of temperature corresponded to an increase of 13% in the monthly incidence rate of DF. In Khanh Hoa, the final model displayed that 1 °C increase in temperature corresponded to an increase of 17% while 100 mm increase in precipitation corresponded to an increase of 11% of DF incidence rate. For Ho Chi Minh City, none of variables were significant in the model. In An Giang, the final model showed that 100 mm increase of precipitation in the preceding and same months corresponded to an increase of 30% and 22% of DF incidence rate.

CONCLUSION

Our findings provide insight into understanding the seasonal pattern and associated climate risk factors.

Dengue Baidu Search Index data can improve the prediction of local dengue epidemic: A case study in Guangzhou, China

BACKGROUND

Dengue fever (DF) in Guangzhou, Guangdong province in China is an important public health issue. The problem was highlighted in 2014 by a large, unprecedented outbreak. In order to respond in a more timely manner and hence better control such potential outbreaks in the future, this study develops an early warning model that integrates internet-based query data into traditional surveillance data.

METHODOLOGY AND PRINCIPAL FINDINGS

A Dengue Baidu Search Index (DBSI) was collected from the Baidu website for developing a predictive model of dengue fever in combination with meteorological and demographic factors. Generalized additive models (GAM) with or without DBSI were established. The generalized cross validation (GCV) score and deviance explained indexes, intraclass correlation coefficient (ICC) and root mean squared error (RMSE), were respectively applied to measure the fitness and the prediction capability of the models. Our results show that the DBSI with one-week lag has a positive linear relationship with the local DF occurrence, and the model with DBSI (ICC:0.94 and RMSE:59.86) has a better prediction capability than the model without DBSI (ICC:0.72 and RMSE:203.29).

CONCLUSIONS

Our study suggests that a DSBI combined with traditional disease surveillance and meteorological data can improve the dengue early warning system in Guangzhou.

The RNAi pathway plays a small part in Wolbachia-mediated blocking of dengue virus in mosquito cells

Wolbachia pipientis is an insect endosymbiont known to limit the replication of viruses including dengue and Zika in their primary mosquito vector, Aedes aegypti. Wolbachia is being released into mosquito populations globally in a bid to control the diseases caused by these viruses. It is theorized that Wolbachia’s priming of the insect immune system may confer protection against subsequent viral infection. Other hypotheses posit a role for competition between Wolbachia and viruses for host cellular resources. Using an A. aegypti cell line infected with Wolbachia, we tested the effects of targeting siRNAs against the major innate immune pathways on dengue virus loads. We show that while Wolbachia infection induces genes in the Toll, JAK/STAT and RNAi pathways, only reduced expression of RNAi leads to a rebound of dengue virus loads in Wolbachia-infected cells. The magnitude of the effect explained less than 10% of the total DENV load, demonstrating that blocking must be dependent on other factors in addition to the expression of RNAi. The findings bode well for the long-term stability of blocking given that immunity gene expression would likely be highly plastic and susceptible to rapid evolution.

Spatio-temporal and neighborhood characteristics of two dengue outbreaks in two arid cities of Mexico

Little is currently known about the spatial-temporal dynamics of dengue epidemics in arid areas. This study assesses dengue outbreaks that occurred in two arid cities of Mexico, Hermosillo and Navojoa, located in northern state of Sonora. Laboratory confirmed dengue cases from Hermosillo (N=2730) and Navojoa (N=493) were geocoded by residence and assigned neighborhood-level characteristics from the 2010 Mexican census. Kernel density and Space-time cluster analysis was performed to detect high density areas and space-time clusters of dengue. Ordinary Least Square regression was used to assess the changing socioeconomic characteristics of cases over the course of the outbreaks. Both cities exhibited contiguous patterns of space-time clustering. Initial areas of dissemination were characterized in both cities by high population density, high percentage of occupied houses, and lack of healthcare. Future research and control efforts in these regions should consider these space-time and socioeconomic patterns.

Toxicity of squamocin on Aedes aegypti larvae, its predators and human cells

BACKGROUND

The mosquito Aedes aegypti transmits a virus that causes diverse human diseases, and control of the vector is an important strategy to avoid disease propagation. Plants in the family Annonaceae are recognised as sources of molecules with uses in the medical and agriculture fields. Molecules of secondary metabolites of Annonaceae plants exhibit insecticidal potential against insect pests and vectors, especially acetogenins, showing high toxicity at low doses, which has encouraged research into producing new insecticide molecules. Herein, we identify an acetogenin from Annona mucosa seeds (chemical analysis) and provide the results of toxicity tests against larvae of A. aegypti (target insect) and its predators Culex bigoti and Toxorhynchites theobaldi (non-target insects) and cytotoxicity to human leukocytes.

RESULTS

We identified squamocin (C₃₇ H₆₆ O₇ ), a fatty acid with a bis-tetrahydrofuran ring. In A. aegypti, this compound caused behavioural disturbance before larval death and high mortality at low concentrations (LC₅₀ = 0.01 µg mL^-1 and LC₉₀ = 0.11 µg mL^-1 ). However, in predators and human leukocytes, squamocin showed no toxicity effect, indicating the selectivity of this molecule for non-target organisms.

CONCLUSION

We identified squamocin from A. mucosa seeds, which exhibited lethal action against A. aegypti and showed selectivity for non-target insects and low cytotoxicity to human cells. © 2016 Society of Chemical Industry.

Data-driven identification of potential Zika virus vectors

Zika is an emerging virus whose rapid spread is of great public health concern. Knowledge about transmission remains incomplete, especially concerning potential transmission in geographic areas in which it has not yet been introduced. To identify unknown vectors of Zika, we developed a data-driven model linking vector species and the Zika virus via vector-virus trait combinations that confer a propensity toward associations in an ecological network connecting flaviviruses and their mosquito vectors. Our model predicts that thirty-five species may be able to transmit the virus, seven of which are found in the continental United States, including Culex quinquefasciatus and Cx. pipiens. We suggest that empirical studies prioritize these species to confirm predictions of vector competence, enabling the correct identification of populations at risk for transmission within the United States.

Network growth models: A behavioural basis for attachment proportional to fitness

Several growth models have been proposed in the literature for scale-free complex networks, with a range of fitness-based attachment models gaining prominence recently. However, the processes by which such fitness-based attachment behaviour can arise are less well understood, making it difficult to compare the relative merits of such models. This paper analyses an evolutionary mechanism that would give rise to a fitness-based attachment process. In particular, it is proven by analytical and numerical methods that in homogeneous networks, the minimisation of maximum exposure to node unfitness leads to attachment probabilities that are proportional to node fitness. This result is then extended to heterogeneous networks, with supply chain networks being used as an example.

Involvement of fatty acid synthase in dengue virus infection

Background

The mosquito transmitted Dengue virus (DENV) remains a significant public health problem in many tropical and subtropical countries. Increasing evidence has suggested that during the infection process cellular lipids play important roles at several stages of the replication cycle. This study sought to characterize the changes in lipid metabolism gene expression and investigated the role of one enzyme, fatty acid synthase, in DENV infection.

Methods

Transcriptional profiles of genes associated with lipid metabolism were evaluated by real-time PCR after infection of different cell lines (HepG2 and HEK293T/17) and with different DENVs (laboratory adapted and low passage). Expression profiles of genes were evaluated by western blotting. A critical lipid metabolism protein, fatty acid synthase was down-regulated through siRNA and inhibited with orlistat and the effect on DENV infection determined by flow cytometry, plaque assay, western blotting and confocal microscopy.

Results

The results showed alterations of gene transcription and expression were seen in genes variously associated with lipogenesis, lipolysis and fatty acid β-oxidation during DENV infection. Interference of fatty acid synthase with either siRNA or orlistat had marked effects on virus production, with orlistat having an EC₅₀ value of 10.07 μM at 24 h post infection. However, non-structural protein expression was largely unaffected.

Conclusions

While drug treatment reduced virus titer by up to 3Log10, no significant effect on DENV non-structural protein expression was observed, suggesting that fatty acid synthase acts through an effect on virion formation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-017-0685-9) contains supplementary material, which is available to authorized users.

Serological evidence of ongoing transmission of dengue virus in permanent residents of Key West, Florida

INTRODUCTION

Dengue fever is the most important mosquito-borne viral disease in the world, with 40% of the global population at risk of infection. Dengue virus is responsible for infections in over 100 countries, including the Americas and Caribbean Basin; however, it has been largely eradicated from the United States through the implementation of effective vector control programs. However, between 2009 and 2010, 27 permanent residents of Key West, Florida, were reported to have locally acquired infections, marking the first autochthonous cases detected in Florida since 1934. Despite this recent and unusual transmission, and the potential risk of serious illness associated with sequential infections, no active surveillance had been conducted since.

MATERIALS AND METHODS

A serosurvey of permanent residents of Key West, Florida, was conducted in March of 2012. After informed consent, enrolled participants (n=173) were given a dengue virus rapid diagnostic test and completed a corresponding questionnaire.

RESULTS

The presence of immunoglobulin G (IgG) antibodies was indicated in 12 participants (6.9%), all of whom reported travel to endemic countries within the past 2 years. Surprisingly, six participants (3.5%) without any recent travel outside the state of Florida gave positive results for IgM antibodies. The presence of birdbaths and bromeliads on the property and sleeping outdoors emerged as significant factors related to previous exposure, whereas home air conditioning without the use of open windows and the use of mosquito repellent were protective.

CONCLUSIONS

These findings suggest local transmission occurred in Key West in early 2012, indicating that transmission may not have subsided in 2010.

A comparative analysis of three vector-borne diseases across Australia using seasonal and meteorological models

Ross River virus (RRV), Barmah Forest virus (BFV), and dengue are three common mosquito-borne diseases in Australia that display notable seasonal patterns. Although all three diseases have been modeled on localized scales, no previous study has used harmonic models to compare seasonality of mosquito-borne diseases on a continent-wide scale. We fit Poisson harmonic regression models to surveillance data on RRV, BFV, and dengue (from 1993, 1995 and 1991, respectively, through 2015) incorporating seasonal, trend, and climate (temperature and rainfall) parameters. The models captured an average of 50–65% variability of the data. Disease incidence for all three diseases generally peaked in January or February, but peak timing was most variable for dengue. The most significant predictor parameters were trend and inter-annual periodicity for BFV, intra-annual periodicity for RRV, and trend for dengue. We found that a Temperature Suitability Index (TSI), designed to reclassify climate data relative to optimal conditions for vector establishment, could be applied to this context. Finally, we extrapolated our models to estimate the impact of a false-positive BFV epidemic in 2013. Creating these models and comparing variations in periodicities may provide insight into historical outbreaks as well as future patterns of mosquito-borne diseases.

Structure in the variability of the basic reproductive number (R0) for Zika epidemics in the Pacific islands

Before the outbreak that reached the Americas in 2015, Zika virus (ZIKV) circulated in Asia and the Pacific: these past epidemics can be highly informative on the key parameters driving virus transmission, such as the basic reproduction number (R0). We compare two compartmental models with different mosquito representations, using surveillance and seroprevalence data for several ZIKV outbreaks in Pacific islands (Yap, Micronesia 2007, Tahiti and Moorea, French Polynesia 2013-2014, New Caledonia 2014). Models are estimated in a stochastic framework with recent Bayesian techniques. R0 for the Pacific ZIKV epidemics is estimated between 1.5 and 4.1, the smallest islands displaying higher and more variable values. This relatively low range of R0 suggests that intervention strategies developed for other flaviviruses should enable as, if not more effective control of ZIKV. Our study also highlights the importance of seroprevalence data for precise quantitative analysis of pathogen propagation, to design prevention and control strategies.

DOI:http://dx.doi.org/10.7554/eLife.19874.001

Zika virus is an infectious disease primarily transmitted between people by mosquitoes. While most people develop mild flu-like symptoms, infection during pregnancy can interfere with how the baby’s head and brain develop. Until recently, the virus had only been seen sporadically in Africa and Asia, but since 2007, outbreaks have been recorded on several Pacific islands. In 2015, the Zika virus reached the Americas, and within six months over 1.5 million cases had been reported in Brazil alone.

There is an urgent need to understand how the Zika virus moves within a population in order to help policymakers, and public health professionals, plan treatment and control of outbreaks of the disease. Researchers often use predictive models to estimate how a disease will spread. A parameter commonly calculated by these models is the “basic reproductive number”, or R₀, which represents the average number of additional cases of the disease caused by one infected individual.

Using models that incorporated data from Zika virus outbreaks that occurred on several Pacific islands, Champagne et al. have produced estimates of R₀ that range from 1.5-4.1.

The R₀ values are greater than one, indicating that infection will spread within a population, but in the same range as those obtained for dengue fever, another closely related mosquito-borne disease. This suggests that by taking appropriate measures, the spread of Zika and dengue can be controlled to similar extents.

A closer look at the relationship between the population size and the predicted R₀ value for each Pacific island revealed an unexpected inverse relationship: the smaller the population, the larger the value of R₀. Since other regional factors may also explain these large differences between settings, further work is needed to disentangle context-specific from disease-specific factors. In this respect, data about seroprevalence (the number of people whose blood shows evidence of a past infection) in different populations is crucial for precisely analyzing the spread of Zika virus.

DOI:http://dx.doi.org/10.7554/eLife.19874.002

A Spatial Hierarchical Analysis of the Temporal Influences of the El Niño-Southern Oscillation and Weather on Dengue in Kalutara District, Sri Lanka

Dengue is the major public health burden in Sri Lanka. Kalutara is one of the highly affected districts. Understanding the drivers of dengue is vital in controlling and preventing the disease spread. This study focuses on quantifying the influence of weather variability on dengue incidence over 10 Medical Officer of Health (MOH) divisions of Kalutara district. Weekly weather variables and data on dengue notifications, measured at 10 MOH divisions in Kalutara from 2009 to 2013, were retrieved and analysed. Distributed lag non-linear model and hierarchical-analysis was used to estimate division specific and overall relationships between weather and dengue. We incorporated lag times up to 12 weeks and evaluated models based on the Akaike Information Criterion. Consistent exposure-response patterns between different geographical locations were observed for rainfall, showing increasing relative risk of dengue with increasing rainfall from 50 mm per week. The strongest association with dengue risk centred around 6 to 10 weeks following rainfalls of more than 300 mm per week. With increasing temperature, the overall relative risk of dengue increased steadily starting from a lag of 4 weeks. We found similarly a strong link between the Oceanic Niño Index to weather patterns in the district in Sri Lanka and to dengue at a longer latency time confirming these relationships. Part of the influences of rainfall and temperature can be seen as mediator in the causal pathway of the Ocean Niño Index, which may allow a longer lead time for early warning signals. Our findings describe a strong association between weather, El Niño-Southern Oscillation and dengue in Sri Lanka.

Dengue fever outbreaks in Eritrea, 2005-2015: A case for strengthening surveillance, control and reporting

Background

The geographic distribution and burden of dengue is increasing globally. This study aims to evaluate dengue outbreaks and to substantiate the need for strengthened surveillance, reporting and control in Eritrea.

Methods

Data from two cross-sectional dengue epidemic investigations in 2005 and 2010 were analyzed. Samples were tested for dengue virus-specific IgM and IgG antibodies using capture enzyme-linked immunosorbent assays. Dengue vectors’ breeding attributes were characterized and epidemic risk indices determined. National routine surveillance weekly reports from 2005 to the second quarter of 2015 were analyzed for spatiotemporal trends.

Results

Dengue outbreaks increased in Eritrea from 2005 to 2015 with clinical presentation varying markedly among patients. The house and container indices for Aedes aegypti were 40 and 39.6 % respectively, with containers having A. aeqypti varying significantly (P < 0.04). Serum from 33.3 % (n = 15) and 88 % (n = 26) of clinical dengue cases in Aroget sub-Zoba (district) of Gash Barka Zoba (region) contained anti-DENV IgM antibody in 2005 and 2006, respectively. The national surveillance data from 2005 to 2015 indicate an overall spatiotemporal increase of dengue fever.

Conclusions

The increase in dengue outbreaks has been confirmed in Eritrea and necessitates strengthening of surveillance and health worker and laboratory capacity, as well as targeted vector control interventions.

The spread of Zika and the potential for global arbovirus syndemics

It is estimated that over a million people die each year from infectious diseases of zoonotic origin and hundreds of millions suffer from these pervasive threats to human well-being. In light of the emergent global concern over the Zika virus, evidence that it has not one but two competent mosquito vector species in the Aedes family, and that both can be co-infected with other pathogens including dengue and chikungunya, this paper examines research suggesting the prospect of significant twenty-first-century outbreaks of arbovirus syndemics. Uniting the concepts 'synergy' with 'epidemic', a syndemics approach recognises that diseases in a population occur neither independent of social and ecological conditions, nor in isolation from other diseases. Assessment of the potential for arbovirus syndemics entails a review of the human role in the global spread of Aedes mosquitoes, the socio-environmental conditions of Aedes diffusion, the increasing likelihood of co-transmission of arbovirus diseases, evidence of co-infection and concern about the adverse health effects of arbovirus syndemic interaction, and the need for an appropriate environment-sensitive framework for effective public health responses. Called Planetary Health, this emergent framework confronts conceptual, knowledge, and governance challenges created by the dramatic shifts in environments, climates, people, vectors, and pathogens in the world.

Reported Distribution of Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus in the United States, 1995-2016 (Diptera: Culicidae)

Aedes (Stegomyia) aegypti (L.) and Aedes (Stegomyia) albopictus (Skuse) transmit arboviruses that are increasing threats to human health in the Americas, particularly dengue, chikungunya, and Zika viruses. Epidemics of the associated arboviral diseases have been limited to South and Central America, Mexico, and the Caribbean in the Western Hemisphere, with only minor localized outbreaks in the United States. Nevertheless, accurate and up-to-date information for the geographical ranges of Ae. aegypti and Ae. albopictus in the United States is urgently needed to guide surveillance and enhance control capacity for these mosquitoes. We compiled county records for presence of Ae. aegypti and Ae. albopictus in the United States from 1995-2016, presented here in map format. Records were derived from the Centers for Disease Control and Prevention ArboNET database, VectorMap, the published literature, and a survey of mosquito control agencies, university researchers, and state and local health departments. Between January 1995 and March 2016, 183 counties from 26 states and the District of Columbia reported occurrence of Ae. aegypti, and 1,241 counties from 40 states and the District of Columbia reported occurrence of Ae. albopictus. During the same time period, Ae. aegypti was collected in 3 or more years from 94 counties from 14 states and the District of Columbia, and Ae. albopictus was collected during 3 or more years from 514 counties in 34 states and the District of Columbia. Our findings underscore the need for systematic surveillance of Ae. aegypti and Ae. albopictus in the United States and delineate areas with risk for the transmission of these introduced arboviruses.