Molecular typing of dengue virus type 2 in Brazil

Suppression of TGF-β/Smad2 signaling by GW788388 enhances DENV-2 clearance in macrophages

Dengue fever, caused by the dengue virus (DENV‐1, −2, −3, and −4), affects millions of people in the tropical and subtropical regions worldwide. Severe dengue is correlated with high viraemia and cytokine storm, such as high levels of transforming growth factor‐β1 (TGF‐β1) in the patient's serum. Here, the TGF‐β1 signaling was investigated in the context of in vitro viral clearance. Macrophages were infected with DENV‐2 at MOI 5 and treated with the TGF‐β receptor 1 and 2 inhibitor, GW788388. TGF‐β1 expression, signal transduction and viral load were evaluated 48 h after DENV‐2 infection by enzyme‐linked immunoassay, immunofluorescence, and RT‐qPCR assays. Total TGF‐β1 level was reduced in 15% after DENV‐2 infection, but the secretion of its biologically active form increased threefold during infection, which was followed by the phosphorylation of Smad2 protein. Phosphorylation of Smad2 was reduced by treatment with GW788388 and it was correlated with reduced cytokine production. Importantly, treatment led to a dose‐dependent reduction in viral load, ranging from 6.6 × 10⁵ RNA copies/ml in untreated cultures to 2.3 × 10³ RNA copies/ml in cultures treated with 2 ng/ml of GW788388. The anti‐TGF‐β1 antibody treatment also induced a significant reduction in viral load to 1.6 × 10³ RNA copies/ml. On the other hand, the addition of recombinant TGF‐β1 in infected cultures promoted an increase in viral load to 7.0 × 10⁶ RNA copies/ml. These results support that TGF‐β1 plays a significant role in DENV‐2 replication into macrophages and suggest that targeting TGF‐β1 may represent an alternative therapeutic strategy to be explored in dengue infection.

Detection of post-vaccination enhanced dengue virus infection in macaques: An improved model for early assessment of dengue vaccines

The need for improved dengue vaccines remains since the only licensed vaccine, Dengvaxia, shows variable efficacy depending on the infecting dengue virus (DENV) type, and increases the risk of hospitalization for severe dengue in children not exposed to DENV before vaccination. Here, we developed a tetravalent dengue purified and inactivated vaccine (DPIV) candidate and characterized, in rhesus macaques, its immunogenicity and efficacy to control DENV infection by analyzing, after challenge, both viral replication and changes in biological markers associated with dengue in humans. Although DPIV elicited cross-type and long-lasting DENV-neutralizing antibody responses, it failed to control DENV infection. Increased levels of viremia/RNAemia (correlating with serum capacity at enhancing DENV infection in vitro), AST, IL-10, IL-18 and IFN-γ, and decreased levels of IL-12 were detected in some vaccinated compared to non-vaccinated monkeys, indicating the vaccination may have triggered antibody-dependent enhancement of DENV infection. The dengue macaque model has been considered imperfect due to the lack of DENV-associated clinical signs. However, here we show that post-vaccination enhanced DENV infection can be detected in this model when integrating several parameters, including characterization of DENV-enhancing antibodies, viremia/RNAemia, and biomarkers relevant to dengue in humans. This improved dengue macaque model may be crucial for early assessment of efficacy and safety of future dengue vaccines.

Dengue virus (DENV) is responsible for the most widespread arboviral disease affecting humans. A pre-existing suboptimal immunity to DENV is accepted as being the major risk factor for severe dengue. Thus, if vaccination does not elicit optimal DENV-specific immunity, a vaccine might, instead, increase the risk of severe dengue in vaccinated individuals, as seen with the only licensed vaccine (Dengvaxia) in children naïve to DENV at vaccination. It is thus crucial to assess dengue vaccine safety at the earliest development stages, ideally in the preclinical stage. The dengue macaque model has been used to assess preclinical efficacy of dengue vaccines, with post-challenge DENV replication as the sole efficacy endpoint. However, this model had not predicted the Dengvaxia-associated safety signals. Here we characterized, in macaques, a dengue purified and inactivated vaccine (DPIV) candidate for its immunogenicity and efficacy/safety. Using a multiparameter approach, including characterization of viral replication and biomarkers relevant to dengue/severe dengue in humans, we were able to detect vaccine-associated safety signals in this model. While these results enabled us to discontinue at an early stage the DPIV development, this improved dengue macaque model may also be instrumental for early assessment of efficacy/safety of future dengue vaccines.

Characterization of recent and minimally passaged Brazilian dengue viruses inducing robust infection in rhesus macaques

The macaque is widely accepted as a suitable model for preclinical characterization of dengue vaccine candidates. However, the only vaccine for which both preclinical and clinical efficacy results were reported so far showed efficacy levels that were substantially different between macaques and humans. We hypothesized that this model’s predictive capacity may be improved using recent and minimally passaged dengue virus isolates, and by assessing vaccine efficacy by characterizing not only the post-dengue virus challenge viremia/RNAemia but also the associated-cytokine profile. Ten recent and minimally passaged Brazilian clinical isolates from the four dengue virus serotypes were tested for their infectivity in rhesus macaques. For the strains showing robust replication capacity, the associated-changes in soluble mediator levels, and the elicited dengue virus-neutralizing antibody responses, were also characterized. Three isolates from dengue virus serotypes 1, 2 and 4 induced viremia of high magnitude and longer duration relative to previously reported viremia kinetics in this model, and robust dengue virus-neutralizing antibody responses. Consistent with observations in humans, increased MCP-1, IFN-γ and VEGF-A levels, and transiently decreased IL-8 levels were detected after infection with the selected isolates. These results may contribute to establishing a dengue macaque model showing a higher predictability for vaccine efficacy in humans.

Espirito Santo virus: a new birnavirus that replicates in insect cells

Espirito Santo virus (ESV) is a newly discovered virus recovered as contamination in a sample of a virulent strain of dengue-2 virus (strain 44/2), which was recovered from a patient in the state of Espirito Santo, Brazil, and amplified in insect cells. ESV was found to be dependent upon coinfection with a virulent strain of dengue-2 virus and to replicate in C6/36 insect cells but not in mammalian Vero cells. A sequence of the genome has been produced by de novo assembly and was not found to match to any known viral sequence. An incomplete match to the nucleotide sequence of the RNA-dependent RNA polymerase from Drosophila X virus (DXV), another birnavirus, could be detected. Mass spectrometry analysis of ESV proteins found no matches in the protein data banks. However, peptides recovered by mass spectrometry corresponded to the de novo-assembled sequence by BLAST analysis. The composition and three-dimensional structure of ESV are presented, and its sequence is compared to those of other members of the birnavirus family. Although the virus was found to belong to the family Birnaviridae, biochemical and sequence information for ESV differed from that of DXV, the representative species of the genus Entomobirnavirus. Thus, significant differences underscore the uniqueness of this infectious agent, and its relationship to the coinfecting virus is discussed.

Dengue infection increases the locomotor activity of Aedes aegypti females

Background

Aedes aegypti is the main vector of the virus causing Dengue fever, a disease that has increased dramatically in importance in recent decades, affecting many tropical and sub-tropical areas of the globe. It is known that viruses and other parasites can potentially alter vector behavior. We investigated whether infection with Dengue virus modifies the behavior of Aedes aegypti females with respect to their activity level.

Methods/Principal Findings

We carried out intrathoracic Dengue 2 virus (DENV-2) infections in Aedes aegypti females and recorded their locomotor activity behavior. We observed an increase of up to ∼50% in the activity of infected mosquitoes compared to the uninfected controls.

Conclusions

Dengue infection alters mosquito locomotor activity behavior. We speculate that the higher levels of activity observed in infected Aedes aegypti females might involve the circadian clock. Further studies are needed to assess whether this behavioral change could have implications for the dynamics of Dengue virus transmission.

Molecular genomic approaches to infectious diseases in resource-limited settings

Josefina Coloma and Eva Harris discuss advances in genomics in resource-limited settings and argue that access to training and capacity building in bioinformatics and data mining will be crucial for the future

Wild dengue virus types 1, 2 and 3 viremia in rhesus monkeys

Among the flaviviruses, dengue, with its four serotypes, has spread throughout the tropics. The most advanced vaccines developed so far include live attenuated viruses, which have been tested in humans but none has been licensed. Preclinical testing of dengue vaccine candidates is performed initially in mice and in nonhuman primates. In the latter the main criteria used to assay protection are neutralizing antibodies elicited by the vaccine candidate and the magnitude and duration of peripheral viremia upon challenge of previously immunized animals. Towards the identification of wild-type viruses that could be used in challenge experiments a total of 31 rhesus monkeys were inoculated subcutaneously of wild dengue types 1, 2, and 3 viruses. The viremia caused by the different viruses was variable but it was possible to identify dengue viruses useful as challenge strains.

Dengue virus surveillance: the co-circulation of DENV-1, DENV-2 and DENV-3 in the State of Rio de Janeiro, Brazil

This study presents the results obtained in the monitoring of dengue virus (DENV) transmission in the Greater Metropolitan Region of the State of Rio de Janeiro, in the period 2000-2001. A total of 5324 serum samples from suspected cases of dengue were analysed in order to confirm dengue infection. The introduction of DENV-3 to the region in December 2000 resulted in the co-circulation of three serotypes: DENV-1, DENV-2 and DENV-3. In this study, virus isolation and/or reverse transcriptase PCR (RT-PCR) confirmed 52.3% (42/79) of DENV-3 cases, showing the importance of acute serum samples in the virological surveillance of the disease. Despite the introduction of a new serotype, an outbreak due to DENV-1 was observed in the municipality of Niteroi. The restriction site-specific PCR (RSS-PCR) patterns obtained for DENV-1 and DENV-2 isolated in that period showed that those strains belonged to the subtypes previously circulating in the state. DENV-3 RSS-PCR patterns confirmed that these viruses belonged to subtype C (Sri Lanka/India strains), represented by the strain circulating on the American continent. These data showed the importance of an active surveillance programme in countries where dengue is endemic.

Molecular epidemiology of type 1 and 2 dengue viruses in Brazil from 1988 to 2001

Dengue is a mosquito-borne viral infection that in recent decades has become a major international public health concern. Epidemic dengue fever reemerged in Brazil in 1981. Since 1990 more than one dengue virus serotype has been circulating in this tropical country and increasing rates of dengue hemorrhagic fever and dengue shock syndrome have been detected every year. Some evidence supports the association between the introduction of a new serotype and/or genotype in a region and the appearance of dengue hemorrhagic fever. In order to study the evolutionary relationships and possible detection of the introduction of new dengue virus genotypes in Brazil in the last years, we analyzed partial nucleotide sequences of 52 Brazilian samples of both dengue type 1 and dengue type 2 isolated from 1988 to 2001 from highly endemic regions. A 240-nucleotide-long sequence from the envelope/nonstructural protein 1 gene junction was used for phylogenetic analysis. After comparing the nucleotide sequences originally obtained in this study to those previously studied by others, and analyzing the phylogenetic trees, we conclude that, after the initial introduction of the currently circulating dengue-1 and dengue-2 genotypes in Brazil, there has been no evidence of introduction of new genotypes since 1988. The increasing number of dengue hemorrhagic fever cases seen in Brazil in the last years is probably associated with secondary infections or with the introduction of new serotypes but not with the introduction of new genotypes.

Molecular analysis of the dengue virus type 1 and 2 in Brazil based on sequences of the genomic envelope-nonstructural protein 1 junction region

The genomic sequences of the Envelope-Non-Structural protein 1 junction region (E/NS1) of 84 DEN-1 and 22 DEN-2 isolates from Brazil were determined. Most of these strains were isolated in the period from 1995 to 2001 in endemic and regions of recent dengue transmission in São Paulo State. Sequence data for DEN-1 and DEN-2 utilized in phylogenetic and split decomposition analyses also include sequences deposited in GenBank from different regions of Brazil and of the world. Phylogenetic analyses were done using both maximum likelihood and Bayesian approaches. Results for both DEN-1 and DEN-2 data are ambiguous, and support for most tree bipartitions are generally poor, suggesting that E/NS1 region does not contain enough information for recovering phylogenetic relationships among DEN-1 and DEN-2 sequences used in this study. The network graph generated in the split decomposition analysis of DEN-1 does not show evidence of grouping sequences according to country, region and clades. While the network for DEN-2 also shows ambiguities among DEN-2 sequences, it suggests that Brazilian sequences may belong to distinct subtypes of genotype III.