Antibody Immunity to Zika Virus among Young Children in a Flavivirus-Endemic Area in Nicaragua.

Objective: To understand the dynamics of Zika virus (ZIKV)-specific antibody immunity in children born to mothers in a flavivirus-endemic region during and after the emergence of ZIKV in the Americas. Methods: We performed serologic testing for ZIKV cross-reactive and type-specific IgG in two longitudinal cohorts, which enrolled pregnant women and their children (PW1 and PW2) after the beginning of the ZIKV epidemic in Nicaragua. Quarterly samples from children over their first two years of life and maternal blood samples at birth and at the end of the two-year follow-up period were studied. Results: Most mothers in this dengue-endemic area were flavivirus-immune at enrollment. ZIKV-specific IgG (anti-ZIKV EDIII IgG) was detected in 82 of 102 (80.4%) mothers in cohort PW1 and 89 of 134 (66.4%) mothers in cohort PW2, consistent with extensive transmission observed in Nicaragua during 2016. ZIKV-reactive IgG decayed to undetectable levels by 6-9 months in infants, whereas these antibodies were maintained in mothers at the year two time point. Interestingly, a greater contribution to ZIKV immunity by IgG3 was observed in babies born soon after ZIKV transmission. Finally, 43 of 343 (13%) children exhibited persistent or increasing ZIKV-reactive IgG at ≥9 months, with 10 of 30 (33%) tested demonstrating serologic evidence of incident dengue infection. Conclusions: These data inform our understanding of protective and pathogenic immunity to potential flavivirus infections in early life in areas where multiple flaviviruses co-circulate, particularly considering the immune interactions between ZIKV and dengue and the future possibility of ZIKV vaccination in women of childbearing potential. This study also shows the benefits of cord blood sampling for serologic surveillance of infectious diseases in resource-limited settings.

Severity and Outcomes of Dengue in Hospitalized Jamaican Children in 2018-2019 During an Epidemic Surge in the Americas.

Objective: In 2019, dengue was among the "top-ten threats to global health," with 3.1 million cases reported from the Americas, the highest ever. Simultaneously, Jamaica reported its largest dengue outbreak in 40 years, following Chikungunya and Zika virus epidemics, in 2014 and 2016-2017, respectively. We describe dengue in children admitted to five hospitals in Jamaica during August 2018 through September 2019. Methods: Hospitalized children and adolescents aged 0 to 15 years with dengue were managed using PAHO/WHO criteria. Data were extracted from questionnaires, entered into a dataset on Microsoft Excel version 2016, exported to SPSS version 20 and analyzed. Groups were compared using Student's t-test for normally distributed parametric data. Chi-square analysis, or Fisher's exact test was used for categorical variables. A p-value < 0.05 was considered statistically significant. Results: There were 339 children, 245 (72.3%) aged 1-10 years, males:females 1:1. Classification was "dengue without warning signs" 53 (15.3%), "dengue with warning signs" 218 (64.3%) and "severe dengue" 68 (20%). Co-morbidities were reported in 88 (26%). Hemoglobin SC disease was associated with severe dengue with hemorrhage (p = 0.005). Organ-system involvement occurred in 334 (98.5%) including gastrointestinal 317 (93.5%), hematologic 311 (91.7%) and musculoskeletal 180 (53.1%). Thirty-nine (11.5%) had 5-7 organ-systems involved. Metabolomics emphasized increased hepatic transaminases 245 (72.3%), lactate dehydrogenase 164 (48.4%) and creatine phosphokinase 84 (24.8%) approaching the high thousands (121,560 u/L), both were markers for severe disease (p < 0.002). Thirteen (3.8%) received intensive care. Dengue was laboratory-confirmed in 220 (78.9%): NS1 antigen-positive (218); RT-PCR-positive (23), with an overlap of NS1 antigen and RT-PCR positive (21); DENV-3 serotype (20). Seventeen (5%) died, 16 (94.1%) had severe dengue and 11 (64.7%) succumbed within 24 to 48 h of admission despite resuscitation and transfusion of blood products. Conclusion: Severe dengue with increased attributable mortality occurred in hospitalized children after Jamaica's maiden Zika epidemic.

A mathematical model to describe antibody-dependent enhancement and assess the effect of limiting cloning for plasma cells in heterologous secondary dengue infection.

We propose a mathematical model to study the antibody-dependent enhancement (ADE) phenomenon. Here, we explore the interaction between macrophages, dengue virus and plasma cells, especially the effect of a limitation on plasma cell proliferation, which occurs due to immunological memory. The model has up to three equilibrium points: one virus-free equilibrium and two virus-presence equilibrium, depending on the value of two thresholds. We determine the existence regions for the model equilibrium points and their stability, a sensitivity analysis was performed in the model thresholds. Numerical simulations illustrate that ADE can occur even when the basic reproduction number is less than one.

Dengue Fever, COVID-19 (SARS-CoV-2), and Antibody-Dependent Enhancement (ADE): A Perspective.

SARS-CoV-2 pandemic and recurrent dengue epidemics in tropical countries have turned into a global health threat. While both virus-caused infections may only reveal light symptoms, they can also cause severe diseases. Here, we review the possible antibody-dependent enhancement (ADE) occurrence, known for dengue infections, when there is a second infection with a different virus strain. Consequently, preexisting antibodies do not neutralize infection, but enhance it, possibly by triggering Fcγ receptor-mediated virus uptake. No clinical data exist indicating such mechanism for SARS-CoV-2, but previous coronavirus infections or infection of SARS-CoV-2 convalescent with different SARS-CoV-2 strains could promote ADE, as experimentally shown for antibodies against the MERS-CoV or SARS-CoV spike S protein. © 2020 International Society for Advancement of Cytometry.

Antibody-Dependent Enhancement of Severe Disease Is Mediated by Serum Viral Load in Pediatric Dengue Virus Infections.

BACKGROUND: Low preexisting anti-dengue virus (DENV) antibody levels are associated with elevated disease severity. While antibody-dependent enhancement of dengue is thought to be driven by viral load, this has not been conclusively shown. We evaluated the association between preinfection anti-DENV antibody titers, viral load, and disease severity among 133 dengue cases in a Nicaraguan pediatric cohort study. METHODS: Viral load was quantified in acute-phase serum by real-time reverse transcription polymerase chain reaction and analyzed in relation to preinfection antibody titer (measured by inhibition enzyme-linked immunosorbent assay) and dengue severity, categorized using 3 definitions. RESULTS: Higher viral load was significantly associated with dengue severity; for each increase of 1.0 log10 copies/mL, the odds of severe dengue increased approximately 50%, regardless of severity definition. Viral load at presentation and the odds of severe disease were highest among patients with low to intermediate preinfection antibody titers and lowest among those with the highest antibody titers. We showed the effect of preinfection antibody titer on disease severity was mediated by viral load for each of 3 dengue severity outcomes. CONCLUSIONS: This study demonstrates the association between preinfection anti-DENV antibody titer, serum viral load, and disease severity, and provides evidence for the mechanism of antibody-dependent enhancement in dengue cases.

Biological view of vaccination described by mathematical modellings: from rubella to dengue vaccines.

The only rubella vaccine available in North America is the RA27/3 strain (isolated from the kidney of a rubella-infected fetus and attenuated) licensed in 1979, which substituted HPV77/DE5 strain vaccine due to concerns about waning immunity. The first dengue vaccine (Dengvaxia CYDTDV) was first registered in Mexico in December, 2015, which is a live recombinant tetravalent dengue vaccine. Rubella vaccine was applied since 1969, but tetravalent dengue vaccine is being used in large scale nowadays. In the past, based on unavailable information regarded to rubella vaccine, mathematical models were used to design vaccination schemes in order to avoid congenital rubella syndrome (CRS). Currently, knowing that vaccine does not result in CRS, rubella vaccination is modelled as usual childhood infection. This experience of updated biological knowledge that influenced mathematical modellings of rubella vaccination is taken into account to reflect about the tetravalent dengue vaccine. We also address a discussion about the security of vaccination strategies.

Prior Dengue Virus Infection Is Associated With Increased Viral Load in Patients Infected With Dengue but Not Zika Virus.

To evaluate potential enhancement of Zika virus (ZIKV) infection among patients with prior dengue virus (DENV) infection, we compared loads of viral RNA among patients infected with ZIKV (n = 1070), DENV-2 (n = 312), or DENV-3 (n = 260). Compared to patients without prior DENV infection, patients with prior DENV infection had significantly higher mean loads of viral RNA if infected with DENV-2 (10.6 vs 11.6 log10 GCE/mL, respectively; t test, P < .0001) or DENV-3 (10.3 vs 10.9 log10 GCE/mL; P < .0001), but not ZIKV (4.7 vs 4.7 log10 GCE/mL; P = .959). These findings provide evidence against in vivo enhancement of ZIKV by anti-DENV antibodies.

In-depth characterization of congenital Zika syndrome in immunocompetent mice: Antibody-dependent enhancement and an antiviral peptide therapy.

BACKGROUND: Zika virus (ZIKV) infection during pregnancy may cause major congenital defects, including microcephaly, ocular, articular and muscle abnormalities, which are collectively defined as Congenital Zika Syndrome. Here, we performed an in-depth characterization of the effects of congenital ZIKV infection (CZI) in immunocompetent mice. METHODS: Pregnant dams were inoculated with ZIKV on embryonic day 5.5 in the presence or absence of a sub-neutralizing dose of a pan-flavivirus monoclonal antibody (4G2) to evaluate the potential role of antibody-dependent enhancement phenomenon (ADE) during short and long outcomes of CZI. FINDINGS: ZIKV infection induced maternal immune activation (MIA), which was associated with occurrence of foetal abnormalities and death. Therapeutic administration of AH-D antiviral peptide during the early stages of pregnancy prevented ZIKV replication and death of offspring. In the post-natal period, CZI was associated with a decrease in whole brain volume, ophthalmologic abnormalities, changes in testicular morphology, and disruption in bone microarchitecture. Some alterations were enhanced in the presence of 4G2 antibody. INTERPRETATION: Our results reveal that early maternal ZIKV infection causes several birth defects in immunocompetent mice, which can be potentiated by ADE phenomenon and are associated with MIA. Additionally, antiviral treatment with AH-D peptide may be beneficial during early maternal ZIKV infection. FUND: This work was supported by the Brazilian National Science Council (CNPq, Brazil), Minas Gerais Foundation for Science (FAPEMIG), Funding Authority for Studies and Projects (FINEP), Coordination of Superior Level Staff Improvement (CAPES), National Research Foundation of Singapore and Centre for Precision Biology at Nanyang Technological University.

Cross-Protection of Dengue Virus Infection against Congenital Zika Syndrome, Northeastern Brazil.

The Zika virus outbreak in Latin America resulted in congenital malformations, called congenital Zika syndrome (CZS). For unknown reasons, CZS incidence was highest in northeastern Brazil; one potential explanation is that dengue virus (DENV)-mediated immune enhancement may promote CZS development. In contrast, our analyses of historical DENV genomic data refuted the hypothesis that unique genome signatures for northeastern Brazil explain the uneven dispersion of CZS cases. To confirm our findings, we performed serotype-specific DENV neutralization tests in a case-control framework in northeastern Brazil among 29 Zika virus-seropositive mothers of neonates with CZS and 108 Zika virus-seropositive control mothers. Neutralization titers did not differ significantly between groups. In contrast, DENV seroprevalence and median number of neutralized serotypes were significantly lower among the mothers of neonates with CZS. Supported by model analyses, our results suggest that multitypic DENV infection may protect from, rather than enhance, development of CZS.

A simple mathematical model to describe antibody-dependent enhancement in heterologous secondary infection in dengue.

We develop a mathematical model to describe the role of antibody-dependent enhancement (ADE) in heterologous secondary infections, assuming that antibodies specific to primary dengue virus (DENV) infection are being produced by immunological memory. The model has a virus-free equilibrium (VFE) and a unique virus-presence equilibrium (VPE). VFE is asymptotically stable when VPE is unstable; and unstable, otherwise. Additionally, there is an asymptotic attractor (not a fixed point) due to the fact that the model assumes unbounded increase in memory cells. In the analysis of the model, ADE must be accounted in the initial stage of infection (a window of time of few days), period of time elapsed from the heterologous infection until the immune system mounting an effective response against the secondary infection. We apply the results yielded by model to evaluate ADE phenomonon in heterologous DENV infection. We also associate the possible occurrence of severe dengue with huge viremia mediated by ADE phenomenon.

Improved Immune Responses Against Zika Virus After Sequential Dengue and Zika Virus Infection in Humans.

The high levels of dengue-virus (DENV) seroprevalence in areas where the Zika virus (ZIKV) is circulating and the cross-reactivity between these two viruses have raised concerns on the risk of increased ZIKV disease severity for patients with a history of previous DENV infections. To determine the role of DENV preimmunity in ZIKV infection, we analyzed the T- and B-cell responses against ZIKV in donors with or without previous DENV infection. Using peripheral blood mononuclear cells (PBMCs) from donors living in an endemic area in Colombia, we have identified, by interferon (IFN)-γ enzyme-linked immunospot (ELISPOT) assay, most of the immunodominant ZIKV T-cell epitopes in the nonstructural (NS) proteins NS1, NS3, and NS5. Analyses of the T- and B-cell responses in the same donors revealed a stronger T-cell response against peptides conserved between DENV and ZIKV, with a higher level of ZIKV-neutralizing antibodies in DENV-immune donors in comparison with DENV-naïve donors. Strikingly, the potential for antibody-mediated enhancement of ZIKV infection was reduced in donors with sequential DENV and ZIKV infection in comparison with donors with DENV infection only. Altogether, these data suggest that individuals with DENV immunity present improved immune responses against ZIKV.

Congenital Zika syndrome: Pitfalls in the placental barrier.

Much progress with respect to congenital Zika virus (ZIKV) pathogenesis has been achieved after the 2015 outbreak in Brazil. It is now accepted that ZIKV is vertically transmitted, infects cells of the developing central nervous system and the placenta, yet it is unclear to what extent placental affection contributes to the development of congenital ZIKV. The association between fulminant villitis and severe fetal involvement emerges as a possibility. ZIKV is unique among the Flaviviruses in its ability to be sexually transmitted, possibly responsible for its teratogenicity. Furthermore, there is controversy over the participation of antibody dependent enhancement (ADE) in patients with non-neutralizing anti-Flavivirus antibodies, a phenomenon previously recognized in serious DENV infections. Our aim was to analyze information regarding the contribution of the placental barrier as an actual player in neonatal ZIKV. Therefore, we underwent a systematic review with keywords "Zika virus" and "ZIKV". Articles were screened for relevance concerning the topics of microcephaly, transplacental transmission, sexual transmission, and ADE. We identified variables that affect the severity of congenital Zika syndrome: age of gestation at maternal infection, the extent of placental disruption (villitis), sexual transmission, initial viral replication at the uterine wall, anti-DENV antibodies, and the possibility of antibody-mediated transcytosis of ZIKV through the placenta. These questions may not seem relevant when Zika becomes endemic, and we are no longer witness to the extreme clinical sequelae seen when the virus moves through an immunologically naïve population; however, characterizing the pathogenesis of congenital Zika syndrome will continue to further our understanding.

Indices of anti-dengue immunoglobulin G subclasses in adult Mexican patients with febrile and hemorrhagic dengue in the acute phase.

Heterologous secondary infections are at increased risk of developing dengue hemorrhagic fever (DHF) because of antibody-dependent enhancement (ADE). IgG subclasses can fix and activate complement and bind to Fcɣ receptors. These factors may also play an important role in the development of ADE and thus in the pathogenesis of DHF. The aim of this study was to analyze the indices of anti-dengue IgG subclasses in adult patients with febrile and hemorrhagic dengue in the acute phase. In 2013, 129 patients with dengue fever (DF) and 57 with DHF in Veracruz, Mexico were recruited for this study and anti-dengue IgM and IgG determined by capture ELISA. Anti-dengue IgG subclasses were detected by indirect ELISA. Anti-dengue IgG2 and IgG3 subclasses were detected in patients with dengue. IgG1 increased significantly in the sera of patients with both primary and secondary infections and DHF, but was higher in patients with secondary infections. The IgG4 subclass index was significantly higher in the sera of patients with DHF than in that of those with DF, who were in the early and late acute phase of both primary and secondary infection. In conclusion, indices of subclasses IgG1 and IgG4 were higher in patients with DHF.

Dengue Virus-Specific Antibodies Enhance Brazilian Zika Virus Infection.

Anti-Flavivirus antibodies are highly cross-reactive and may facilitate Zika virus (ZIKV) infection through the antibody-dependent enhancement (ADE) mechanism. We demonstrate that dengue-specific antibodies enhance the infection of a primary Brazilian ZIKV isolate in a FcγRII-expressing K562 cell line. In addition, we demonstrate that serum samples from dengue-immune pregnant women enhanced ZIKV infection. These findings highlight the need for epidemiological studies and animal models to further confirm the role of ADE in the development of congenital and neurological complications associated with ZIKV infections.

Dengue Antibody and Zika: Friend or Foe?

Zika virus is a mosquito-borne Flavivirus related to dengue that is rapidly spreading through the Americas. This outbreak is occurring in dengue-endemic areas where the population has acquired antibodies to dengue. Recent studies reveal that preexisting dengue antibodies may have opposite effects on Zika infection, transmission, and clinical outcome. Discerning these effects is critical to a better understanding of Zika pathogenesis and the prevention of future outbreaks.

Placental Transfer of Dengue Virus (DENV)-Specific Antibodies and Kinetics of DENV Infection-Enhancing Activity in Brazilian Infants.

BACKGROUND: Maternal-fetal transferred dengue virus (DENV)-specific antibodies have been implicated in the immunopathogenesis of dengue during infancy. METHODS: A prospective birth cohort was established in a dengue-endemic area in the Northeast Region of Brazil. DENV-specific immunoglobulin G (IgG) and DENV-1-4 serotype-specific neutralizing antibody (NAb) levels were assessed in 376 paired maternal and umbilical cord blood samples. The kinetics of enhancing activity by maternally acquired DENV antibodies was determined in serum samples from children enrolled in the cohort. RESULTS: Mothers were mostly immune to DENV-3 alone (53.7%) or combined with DENV-4 (30.6%). Levels of DENV-specific IgG, DENV-3 NAbs, and DENV-4 NAbs were significantly higher in newborns than in their respective mothers. Mothers immune to a single serotype transferred greater levels of DENV-specific IgG (P = .02) and DENV-3 NAbs (P = .04) than mothers immune to multiple DENV serotypes. Maternally acquired DENV-3 NAbs disappeared in >90% of the children by the age of 4 months. The peak enhancing activity was detected by the age of 2 months (P < .0001) and rapidly declined by the age of 4 months (P = .0035). CONCLUSIONS: Unlike Asian infants, the enhancing activity of DENV infection by maternally transferred DENV antibodies occurs at earlier ages in Brazilian children. These findings might explain the low occurrence of severe dengue among infants in our setting.

The relevance of dengue virus genotypes surveillance at country level before vaccine approval.

Dengue is a major threat for public health in tropical and subtropical countries around the world. In the absence of a licensed vaccine and effective antiviral therapies, control measures have been based on education activities and vector elimination. Current efforts for developing a vaccine are both promising and troubling. At the advent of the introduction of a tetravalent dengue vaccine, molecular surveillance of the circulating genotypes in different geographical regions has gained considerable importance. A growing body of in vitro, preclinical, and clinical phase studies suggest that vaccine conferred protection in a geographical area could depends on the coincidence of the dengue virus genotypes included in the vaccine and those circulating. In this review we present the state-of-the-art in this field, highlighting the need of deeper knowledge on neutralizing immune response for making decisions about future vaccine approval and the potential need for different vaccine composition for regional administration.

Assessment of bivalent and tetravalent dengue vaccine formulations in flavivirus-naïve adults in Mexico.

UNLABELLED: Several ChimeriVax-Dengue (CYD)-based vaccination strategies were investigated as potential alternatives to vaccination with tetravalent CYD vaccine (CYD-TDV) in this phase IIa trial conducted in 2008-9 in 150 healthy adults. Participants were randomized and vaccinated on D0 and D105 (± 15 days). One group received bivalent CYD vaccine against serotypes 1 and 3 (CYD-1;3) on day 0 and CYD-2;4 on day 105 (± 15 days). Two groups received an injection at each timepoint of a tetravalent blend of CYD-1;3;4 and a VERO cell derived, live attenuated vaccine against serotype 2 (VDV-2), or the reference CYD-TDV. A fourth group received Japanese encephalitis (JE) vaccine on days -14, -7 and 0, followed by CYD-TDV on day 105. Viraemia was infrequent in all groups. CYD-4 viraemia was most frequent after tetravalent vaccination, while CYD-3 viraemia was most frequent after the first bivalent vaccination. Immunogenicity as assessed by 50% plaque reduction neutralisation test on D28 was comparable after the first injection of either tetravalent vaccine, and increased after the second injection, particularly with the blended CYD-1;3;4/ VDV-2 vaccine. In the bivalent vaccine group, immune response against serotype 3 was highest and the second injection elicited a low immune response against CYD 2 and 4. Immune responses after the first injection of CYD-TDV in the JE-primed group were in general higher than after the first injection in the other groups. All tested regimens were well tolerated without marked differences between groups. Bivalent vaccination showed no advantage in terms of immunogenicity. CLINICAL TRIAL REGISTRATION NUMBER: NCT00740155.