Long-term circulation of Zika virus in Thailand: an observational study

Role of non-human primate models in accelerating research and developing countermeasures against Zika virus infection

Zika virus, a mosquito-transmitted orthoflavivirus, has become a pathogen of global health concern ever since the virus caused an epidemic in Brazil in 2015 associated with approximately 700 000 laboratory-confirmed cases of congenital microcephaly. The subsequent spread of the epidemic in 2016 resulted in a wide spectrum of congenital neurological, ophthalmological, and developmental abnormalities across the Americas, Africa, and Asia. In this context, non-human primate models have become essential tools for Zika virus research to understand the pathogenesis of congenital brain injury and perinatal complications and for developing and testing medical countermeasures such as vaccines, diagnostics, and therapeutics. Fetal brain injury has been observed across various non-human primate species and is influenced by factors such as the Zika virus strain, gestational age at inoculation, and inoculation dose and route. Miscarriages are also seen as common outcomes of first trimester Zika virus infections. This Series paper reviews the diverse non-human primate models currently used for Zika virus research to mitigate the public health effects of future Zika virus epidemics.

Estimating transmissibility of Zika virus in Colombia in the presence of surveillance bias

The 2015-2016 Zika virus outbreak in the Americas presented significant challenges in understanding the transmission dynamics due to substantial reporting biases, as women of reproductive age (15-39 years) were disproportionately represented in the surveillance data when public awareness of relationship between Zika and microcephaly increased. Using national surveillance data from Colombia during July 27, 2015-November 21, 2016, we developed a Bayesian hierarchical modeling framework to reconstruct the true numbers of symptomatic cases and estimate transmission parameters while accounting for differential reporting across age-sex groups. Our model revealed that the detection rate of symptomatic cases among women of reproductive age was 99% (95% CI: 98.7-100), compared to 85.4% (95% CI: 84.7-86.1) in other demographic groups. After correcting for these biases, our results showed that females aged 15-39 years remained 82.8% (95% CI: 80.2-85.2%) more susceptible to Zika symptomatic infection than males of the same age, independent of differential reporting areas. Departments with medium-high altitude, medium-high population density, low coverage of forest, or high dengue incidence from 2011-2015 exhibited greater Zika risk. This study underscores the importance of accounting for surveillance biases in epidemiological studies to better understand factors influencing Zika transmission and to inform disease control and prevention.

A Review of the Recent Epidemiology of Zika Virus Infection

Zika virus (ZIKV) is a flavivirus transmitted primarily by the bite of infected Aedes species mosquitoes. Although typically asymptomatic or causing mild symptoms and infrequent neurological disease in older children and adults, infection during pregnancy can result in severe congenital malformations and neurodevelopmental deficits. We conducted a review of published literature and official data sources to describe recent Zika epidemiological trends, building on WHO updates posted in 2019 and 2022. Globally, cases declined after the height of ZIKV transmission in the Americas in 2015-2016; however, transmission continues across multiple regions, with intermittent outbreaks reported. As of December 2023, there is documented evidence of current or prior autochthonous mosquito-borne ZIKV transmission in 92 countries and territories; most recently, Guinea, Mali, and Sri Lanka were included on the basis of recent or retrospective testing of specimens collected during surveillance activities or studies. The abundance of asymptomatic and mild infections and limited diagnostic testing suggest that transmission in many locations likely remains underrecognized. Public health authorities, clinicians, communities at risk, and travelers should remain alert to the possibility of ZIKV transmission and implement measures to limit the risk of infection with ZIKV and other Aedes-borne arboviruses. To strengthen surveillance for ZIKV infections and congenital disease, targeted surveillance using clear case definitions and epidemiologically appropriate laboratory testing algorithms should be applied.

IgA-driven neutrophil activation underlies post-Zika severe dengue disease in humans

The four dengue virus serotypes (DENV1-4) and the related Zika flavivirus (ZIKV) are major public health concerns worldwide. Primary immunity against ZIKV increases the risk of a subsequent severe DENV2 infection, presenting a significant challenge for developing safe and effective ZIKV vaccines. However, the mechanisms driving this phenomenon remain unclear. Leveraging our long-standing Pediatric Dengue Cohort Study in Nicaragua, we show that serum anti-NS1 IgA antibodies elicited after a primary ZIKV infection drive neutrophil activation and correlate with increased risk of subsequent severe DENV2 disease. Depletion experiments combined with ex vivo functional NETosis assays confirmed that anti-NS1 IgA antibodies drive neutrophil activation in dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Moreover, increased neutrophil degranulation in paired serum samples obtained during the acute DENV2 infection from the same individuals correlated with IgA binding to DENV2 NS1 and preceded the development of vascular leakage. This finding was corroborated in an orthogonal hospital-based study. Thus, serum anti-NS1 IgA enhances neutrophil activation in severe dengue, with implications for prognostics, therapeutics, and vaccines.

Modelling the impact and cost-effectiveness of upcoming Zika virus vaccines on congenital Zika syndrome

BACKGROUND

Zika virus (ZIKV) continues to circulate in Southeast Asia following the 2015-2016 global epidemic, posing an ongoing risk of importation and disease spread for Singapore, a tropical city-state in the region. The virus remains a threat to pregnant women and their fetuses due to the risk of Congenital Zika Syndrome (CZS). Vaccines currently in development offer hope for reducing ZIKV infections and CZS cases.

METHODS

We developed an agent-based compartmental model, incorporating Singapore's demographic dynamics, to simulate ZIKV epidemic trajectories and project the national disease burden of CZS over the next decade. We proposed eight vaccination strategies targeting females of child-bearing age and evaluated their cost-effectiveness-in terms of the incremental cost-effectiveness ratio (ICER)-across scenarios with varying vaccine efficacy, protection duration, coverage rate, vaccination cost, and pre-existing immunity levels in the population.

RESULTS

Continuous high importation of ZIKV could lead to multiple small outbreaks in the next decade. Total CZS case numbers over the next decade were projected to be 68 (95 % confidence interval [CI]: 66-70), 51 (95 % CI: 49-52), and 32 (95 % CI: 31-33) under scenarios of 0 %, 2 %, and 5 % pre-existing immunity, respectively. While mass vaccination for females would avert up to 66 (95 % CI: 64-69), 49 (95 % CI: 48-50), and 31 (95 % CI: 30-31) CZS cases, respectively, the cost-effectiveness of these strategies should be evaluated on a case-by-case basis. The pre-pregnancy vaccination strategy demonstrated consistent cost-effectiveness regardless of vaccine protection duration, vaccine efficacy, vaccine price, or pre-existing immunity level in the population.

CONCLUSIONS

Localised outbreaks driven by importation are likely to persist in Singapore. The pre-pregnancy vaccination strategy is consistently cost-effective and should be considered. Mass vaccination may also be viable with the availability of a low-cost vaccine providing long-term protection.

Zika virus: advancing a priority research agenda for preparedness and response

The 2015-16 Zika virus epidemic emerged in the Americas and rapidly spread throughout the region and beyond, showing the epidemic potential of this mosquito-borne Orthoflavivirus and its capacity to cause severe congenital malformations and neurological sequelae. WHO declared the Zika virus epidemic a public health emergency of international concern in 2016. Despite this declaration, there are no licensed Zika virus vaccines, therapeutics, or diagnostic tests appropriate for routine antenatal screening. To address this absence of essential tools to detect and mitigate the threat of future Zika virus outbreaks, a group of global experts developed a priority agenda for Zika virus research and development. This Series paper summarises crucial challenges and knowledge gaps and outlines a comprehensive strategy to advance research, surveillance, global capacity, policy, and investment for Zika virus preparedness and response.

Zika Virus Infection in Pregnant Traveler Returning to Denmark from Phuket, Thailand, 2024

We report a case of Zika virus (ZIKV) infection in a pregnant woman from Denmark who traveled to Thailand during her first trimester. Late in the second trimester, severe microcephaly was diagnosed in the fetus, and ZIKV infection was confirmed. Travelers and clinicians should be aware of ongoing ZIKV risk in Thailand.

Reconciling heterogeneous dengue virus infection risk estimates from different study designs

Uncovering rates at which susceptible individuals become infected with a pathogen, i.e., the force of infection (FOI), is essential for assessing transmission risk and reconstructing distribution of immunity in a population. For dengue, reconstructing exposure and susceptibility statuses from the measured FOI is of particular significance as prior exposure is a strong risk factor for severe disease. FOI can be measured via many study designs. Longitudinal serology is considered gold standard measurements, as they directly track the transition of seronegative individuals to seropositive due to incident infections (seroincidence). Cross-sectional serology can provide estimates of FOI by contrasting seroprevalence across ages. Age of reported cases can also be used to infer FOI. Agreement of these measurements, however, has not been assessed. Using 26 y of data from cohort studies and hospital-attended cases from Kamphaeng Phet province, Thailand, we found FOI estimates from the three sources to be highly inconsistent. Annual FOI estimates from seroincidence were 1.75 to 4.05 times higher than case-derived FOI. Seroprevalence-derived was moderately correlated with case-derived FOI (correlation coefficient = 0.47) with slightly lower estimates. Through extensive simulations and theoretical analysis, we show that incongruences between methods can result from failing to account for dengue antibody kinetics, assay noise, and heterogeneity in FOI across ages. Extending standard inference models to include these processes reconciled the FOI and susceptibility estimates. Our results highlight the importance of comparing inferences across multiple data types to uncover additional insights not attainable through a single data type/analysis.

Comprehensive phylogenomic analysis of Zika virus: Insights into its origin, past evolutionary dynamics, and global spread

BACKGROUND

Zika virus (ZIKV), a Flaviviridae family member, has been linked to severe neurological disorders. Despite detailed studies on recent outbreaks, the early evolutionary history of ZIKV remains partially unclear. This study elucidates ZIKV origin and evolutionary dynamics, focusing on recombination events, early lineage diversification, and virus spread across continents.

METHODS

We assessed recombination using multiple methods. We conducted Bayesian phylogenetic analyses to understand the evolutionary relationships and timing of key diversification events. Model selection was carried out to determine the most appropriate evolutionary model for our dataset.

RESULTS

Our phylogenies revealed recent recombination between Singaporean and African lineages, indicating the co-circulation of diverse lineages during outbreaks. Thailand was identified as a crucial hub in the spread across Asia. The phylogenetic analysis suggests that the ZIKV lineage dates back to the eleventh century, with the first significant diversification occurring in the nineteenth century. The timing of the re-introduction of the Asian lineage into Africa and the delay between probable introduction and outbreak onset were also determined.

CONCLUSIONS

This study provides novel insights into ZIKV's origin and early evolutionary dynamics, highlighting Thailand's role in the spread of the virus in Asia and recent recombination events between distant lineages. These findings emphasize the need for continuous surveillance and a better understanding of ZIKV biology to forecast and mitigate future outbreaks.

Detection of anti-premembrane antibody as a specific marker of four flavivirus serocomplexes and its application to serosurveillance in endemic regions

In the past few decades, several emerging/re-emerging mosquito-borne flaviviruses have resulted in disease outbreaks of public health concern in the tropics and subtropics. Due to cross-reactivities of antibodies recognizing the envelope protein of different flaviviruses, serosurveillance remains a challenge. Previously we reported that anti-premembrane (prM) antibody can discriminate between three flavivirus infections by Western blot analysis. In this study, we aimed to develop a serological assay that can discriminate infection or exposure with flaviviruses from four serocomplexes, including dengue (DENV), Zika (ZIKV), West Nile (WNV) and yellow fever (YFV) viruses, and explore its application for serosurveillance in flavivirus-endemic countries. We employed Western blot analysis including antigens of six flaviviruses (DENV1, 2 and 4, WNV, ZIKV and YFV) from four serocomplexes. We tested serum samples from YF-17D vaccinees, and from DENV, ZIKV and WNV panels that had been confirmed by RT-PCR or by neutralization assays. The overall sensitivity/specificity of anti-prM antibodies for DENV, ZIKV, WNV, and YFV infections/exposure were 91.7%/96.4%, 91.7%/99.2%, 88.9%/98.3%, and 91.3%/92.5%, respectively. When testing 48 samples from Brazil, we identified multiple flavivirus infections/exposure including DENV and ZIKV, DENV and YFV, and DENV, ZIKV and YFV. When testing 50 samples from the Philippines, we detected DENV, ZIKV, and DENV and ZIKV infections with a ZIKV seroprevalence rate of 10%, which was consistent with reports of low-level circulation of ZIKV in Asia. Together, these findings suggest that anti-prM antibody is a flavivirus serocomplex-specific marker and can be employed to delineate four flavivirus infections/exposure in regions where multiple flaviviruses co-circulate.

Synergistic Larvicidal and Pupicidal Toxicity and the Morphological Impact of the Dengue Vector (Aedes aegypti) Induced by Geranial and trans-Cinnamaldehyde

Monoterpenes are effective and eco-friendly alternatives to conventional chemical larvicides. We tested single and binary mixtures of monoterpenes-geranial and trans-cinnamaldehyde-for their larvicidal and pupicidal activities against Aedes aegypti L. and for non-target toxicity on guppies (Poecilia reticulata Peters), using 1% (w/w) temephos as a reference. Geranial and trans-cinnamaldehyde at 250 ppm showed stronger larvicidal and pupicidal activities with a 100% mortality rate and an LT50 ranging from 0.3 to 0.6 h. All combinations were strongly synergistic against larvae and pupae compared to single formulations, with an increased mortality value (IMV) of 6% to 93%. The combination of geranial + trans-cinnamaldehyde (1:1) at 200 ppm showed the highest impact, with an IMV of 93%. The strongest larvicidal and pupicidal activities, a 100% mortality rate, and an LT50 of 0.2 h were achieved by geranial + trans-cinnamaldehyde (1:1) 500 ppm. They were thirty times more effective than a 1% temephos solution (LT50 ranging from 6.7 to 96 h) and caused obviously shriveled cuticles and a swollen respiratory system. All single and binary mixtures were not toxic to the guppies. Thus, the combination of geranial + trans-cinnamaldehyde has great potential as a safe insecticide for controlling mosquito larvae and pupae.

Reconciling heterogeneous dengue virus infection risk estimates from different study designs

Uncovering rates at which susceptible individuals become infected with a pathogen, i.e. the force of infection (FOI), is essential for assessing transmission risk and reconstructing distribution of immunity in a population. For dengue, reconstructing exposure and susceptibility statuses from the measured FOI is of particular significance as prior exposure is a strong risk factor for severe disease. FOI can be measured via many study designs. Longitudinal serology are considered gold standard measurements, as they directly track the transition of seronegative individuals to seropositive due to incident infections (seroincidence). Cross-sectional serology can provide estimates of FOI by contrasting seroprevalence across ages. Age of reported cases can also be used to infer FOI. Agreement of these measurements, however, have not been assessed. Using 26 years of data from cohort studies and hospital-attended cases from Kamphaeng Phet province, Thailand, we found FOI estimates from the three sources to be highly inconsistent. Annual FOI estimates from seroincidence was 2.46 to 4.33-times higher than case-derived FOI. Correlation between seroprevalence-derived and case-derived FOI was moderate (correlation coefficient=0.46) and no systematic bias. Through extensive simulations and theoretical analysis, we show that incongruences between methods can result from failing to account for dengue antibody kinetics, assay noise, and heterogeneity in FOI across ages. Extending standard inference models to include these processes reconciled the FOI and susceptibility estimates. Our results highlight the importance of comparing inferences across multiple data types to uncover additional insights not attainable through a single data type/analysis.

Japanese encephalitis virus E protein domain III immunization mediates cross-protection against Zika virus in mice via antibodies and CD8+T cells

Zika virus (ZIKV) and Japanese encephalitis virus (JEV) are antigenically related flaviviruses that co-circulate in many countries/territories. The interaction between the two viruses needs to be determined. Recent findings by ourselves and other labs showed that JEV-elicited antibodies (Abs) and CD8+T cells exacerbate and protect against subsequent ZIKV infection, respectively. However, the impact of JEV envelope (E) protein domain III (EDIII)-induced immune responses on ZIKV infection is unclear. We show here that sera from JEV-EDIII-vaccinated mice cross-react with ZIKV-EDIII in vitro, and transfer of the same sera to mice significantly decreases death upon lethal ZIKV infection at a dose-dependent manner. Maternally acquired anti-JEV-EDIII Abs also significantly reduce the mortality of neonatal mice born to JEV-EDIII-immune mothers post ZIKV challenge. Similarly, transfer of ZIKV-EDIII-reactive IgG purified from JEV-vaccinated humans increases the survival of ZIKV-infected mice. Notably, transfer of an extremely low volume of JEV-EDIII-immune sera or ZIKV-EDIII-reactive IgG does not mediate the Ab-mediated enhancement (ADE) of ZIKV infection. Similarly, transfer of JEV-EDIII-elicited CD8+T cells protects recipient mice against ZIKV challenge. These results demonstrate that JEV-EDIII-induced immune components including Abs and T cells have protective roles in ZIKV infection, suggesting EDIII is a promising immunogen for developing effective and safety JEV vaccine.

Predicting Efficacy of a Purified Inactivated Zika Virus Vaccine in Flavivirus-Naïve Humans Using an Immunological Correlate of Protection in Non-Human Primates

A traditional phase 3 clinical efficacy study for a Zika vaccine may be unfeasible because of the current low transmission of Zika virus (ZIKV). An alternative clinical development approach to evaluate Zika vaccine efficacy (VE) is therefore required, delineated in the US FDA's Accelerated Approval Program for licensure, which utilizes an anti-Zika neutralizing antibody (Zika NAb) titer correlated with non-human primate (NHP) protection as a surrogate endpoint. In this accelerated approval approach, the estimation of VE would be inferred from the percentage of phase 3 trial participants achieving the established surrogate endpoint. We provide a statistical framework to predict the probability of protection for human participants vaccinated with a purified inactivated ZIKV vaccine (TAK-426), in the absence of VE measurements, using NHP data under a single-correlate model. Based on a logistic regression (LR) with bias-reduction model, a probability of 90% protection in humans is expected with a ZIKV NAb geometric mean titer (GMT) ≥ 3.38 log10 half-maximal effective concentration (EC50). The predicted probability of protection of TAK-426 against ZIKV infection was determined using the two-parameter LR model that fit the calculated VE in rhesus macaques and the flavivirus-naïve phase 1 trial participants' ZIKV NAb GMTs log10 EC50, measured by a ZIKV reporter virus particle assay, at 1 month post dose 2. The TAK-426 10 µg dose predicted a probability of protection from infection of 98% among flavivirus-naïve phase 1 trial participants.

Identification and characterization of a nonbiological small-molecular mimic of a Zika virus conformational neutralizing epitope

Antigenic similarities between Zika virus (ZIKV) and other flaviviruses pose challenges to the development of virus-specific diagnostic tools and effective vaccines. Starting with a DNA-encoded one-bead-one-compound combinatorial library of 508,032 synthetic, non-natural oligomers, we selected and characterized small molecules that mimic ZIKV epitopes. High-throughput fluorescence-activated cell sorter-based bead screening was used to select molecules that bound IgG from ZIKV-immune but not from dengue-immune sera. Deep sequencing of the DNA from the "Zika-only" beads identified 40 candidate molecular structures. A lead candidate small molecule "CZV1-1" was selected that correctly identifies serum specimens from Zika-experienced patients with good sensitivity and specificity (85.3% and 98.4%, respectively). Binding competition studies of purified anti-CZV1-1 IgG against known ZIKV-specific monoclonal antibodies (mAbs) showed that CZV1-1 mimics a nonlinear, neutralizing conformational epitope in the domain III of the ZIKV envelope. Purified anti-CZV1-1 IgG neutralized infection of ZIKV in cell cultures with potencies comparable to highly specific ZIKV-neutralizing mAbs. This study demonstrates an innovative approach for identification of synthetic non-natural molecular mimics of conformational virus epitopes. Such molecular mimics may have value in the development of accurate diagnostic assays for Zika, as well as for other viruses.

Characteristics, risk factors, and outcomes related to Zika virus infection during pregnancy in Northeastern Thailand: A prospective pregnancy cohort study, 2018-2020

BACKGROUND

In response to the 2015-2016 Zika virus (ZIKV) outbreak and the causal relationship established between maternal ZIKV infection and adverse infant outcomes, we conducted a cohort study to estimate the incidence of ZIKV infection in pregnancy and assess its impacts in women and infants.

METHODOLOGY/PRINCIPAL FINDINGS

From May 2018-January 2020, we prospectively followed pregnant women recruited from 134 participating hospitals in two non-adjacent provinces in northeastern Thailand. We collected demographic, clinical, and epidemiologic data and blood and urine at routine antenatal care visits until delivery. ZIKV infections were confirmed by real-time reverse transcriptase polymerase chain reaction (rRT-PCR). Specimens with confirmed ZIKV underwent whole genome sequencing. Among 3,312 women enrolled, 12 (0.36%) had ZIKV infections, of which two (17%) were detected at enrollment. Ten (83%, 3 in 2nd and 7 in 3rd trimester) ZIKV infections were detected during study follow-up, resulting in an infection rate of 0.15 per 1,000 person-weeks (95% CI: 0.07-0.28). The majority (11/12, 91.7%) of infections occurred in one province. Persistent ZIKV viremia (42 days) was found in only one woman. Six women with confirmed ZIKV infections were asymptomatic until delivery. Sequencing of 8 ZIKV isolates revealed all were of Asian lineage. All 12 ZIKV infected women gave birth to live, full-term infants; the only observed adverse birth outcome was low birth weight in one (8%) infant. Pregnancies in 3,300 ZIKV-rRT-PCR-negative women were complicated by 101 (3%) fetal deaths, of which 67 (66%) had miscarriages and 34 (34%) had stillbirths. There were no differences between adverse fetal or birth outcomes of live infants born to ZIKV-rRT-PCR-positive mothers compared to live infants born to ZIKV-rRT-PCR-negative mothers.

CONCLUSIONS/SIGNIFICANCE

Confirmed ZIKV infections occurred infrequently in this large pregnancy cohort and observed adverse maternal and birth outcomes did not differ between mothers with and without confirmed infections.

Structural basis of Zika virus NS1 multimerization and human antibody recognition

Zika virus (ZIKV) belongs to the Flavivirus genus of the Flaviviridae family along with the four serotypes of dengue virus (DENV1-4). The recent global outbreaks of contemporary ZIKV strains demonstrated that infection can lead to neurological sequelae in adults and severe abnormalities in newborns that were previously unreported with ancestral strains. As such, there remains an unmet need for efficacious vaccines and antiviral agents against ZIKV. The non-structural protein 1 (NS1) is secreted from the infected cell and is thought to be associated with disease severity besides its proven usefulness for differential diagnoses. However, its physiologically relevant structure and pathogenesis mechanisms remain unclear. Here, we present high-resolution cryoEM structures of ZIKV recombinant secreted NS1 (rsNS1) and its complexes with three human monoclonal antibodies (AA12, EB9, GB5), as well as evidence for ZIKV infection-derived secreted NS1 (isNS1) binding to High Density Lipoprotein (HDL). We show that ZIKV rsNS1 forms tetramers and filamentous repeats of tetramers. We also observed that antibody binding did not disrupt the ZIKV NS1 tetramers as they bound to the wing and connector subdomain of the β-ladder. Our study reveals new insights into NS1 multimerization, highlights the need to distinguish the polymorphic nature of rsNS1 and isNS1, and expands the mechanistic basis of the protection conferred by antibodies targeting NS1.

Global seroprevalence of Zika virus in asymptomatic individuals: A systematic review

BACKGROUND

Zika virus (ZIKV) has spread to five of the six World Health Organization (WHO) regions. Given the substantial number of asymptomatic infections and clinical presentations resembling those of other arboviruses, estimating the true burden of ZIKV infections is both challenging and essential. Therefore, we conducted a systematic review and meta-analysis of seroprevalence studies of ZIKV IgG in asymptomatic population to estimate its global impact and distribution.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted extensive searches and compiled a collection of articles published from Jan/01/2000, to Jul/31/2023, from Embase, Pubmed, SciELO, and Scopus databases. The random effects model was used to pool prevalences, reported with their 95% confidence interval (CI), a tool to assess the risk of study bias in prevalence studies, and the I2 method for heterogeneity (PROSPERO registration No. CRD42023442227). Eighty-four studies from 49 countries/territories, with a diversity of study designs and serological tests were included. The global seroprevalence of ZIKV was 21.0% (95%CI 16.1%-26.4%). Evidence of IgG antibodies was identified in all WHO regions, except for Europe. Seroprevalence correlated with the epidemics in the Americas (39.9%, 95%CI:30.0-49.9), and in some Western Pacific countries (15.6%, 95%CI:8.2-24.9), as well as with recent and past circulation in Southeast Asia (22.8%, 95%CI:16.5-29.7), particularly in Thailand. Additionally, sustained low circulation was observed in Africa (8.4%, 95%CI:4.8-12.9), except for Gabon (43.7%), and Burkina Faso (22.8%). Although no autochthonous transmission was identified in the Eastern Mediterranean, a seroprevalence of 16.0% was recorded.

CONCLUSIONS/SIGNIFICANCE

The study highlights the high heterogeneity and gaps in the distribution of seroprevalence. The implementation of standardized protocols and the development of tests with high specificity are essential for ensuring a valid comparison between studies. Equally crucial are vector surveillance and control methods to reduce the risk of emerging and re-emerging ZIKV outbreaks, whether caused by Ae. aegypti or Ae. albopictus or by the Asian or African ZIKV.

Design, synthesis, and antiviral activity of 1-aryl-4-arylmethylpiperazine derivatives as Zika virus inhibitors with broad antiviral spectrum

Zika virus (ZIKV) disease has been given attention due to the risk of congenital microcephaly and neurodevelopmental disorders after ZIKV infection in pregnancy, but no vaccine or antiviral drug is available. Based on a previously reported ZIKV inhibitor ZK22, a series of novel 1-aryl-4-arylmethylpiperazine derivatives was designed, synthesized, and investigated for antiviral activity by quantify cellular ZIKV RNA amount using RT-qPCR method in ZIKV-infected human venous endothelial cells (HUVECs) assay. Structure-activity relationship (SAR) analysis demonstrated that anti-ZIKV activity of 1-aryl-4-arylmethylpiperazine derivatives is not correlated with molecular hydrophobicity, multiple new derivatives with pyridine group to replace the benzonitrile moiety of ZK22 showed stronger antiviral activity, higher ligand lipophilicity efficiency as well as lower cytotoxicity. Two active compounds 13 and 33 were further identified as novel ZIKV entry inhibitors with the potential of oral available. Moreover, both ZK22 and newly active derivatives also possess of obvious inhibition on the viral replication of coronavirus and influenza A virus at low micromolar level. In summary, this work provided better candidates of ZIKV inhibitor for preclinical study and revealed the promise of 1-aryl-4-arylmethylpiperazine chemotype in the development of broad-spectrum antiviral agents.

Sequence Data From a Travel-Associated Case of Microcephaly Highlight a Persisting Risk due to Zika Virus Circulation in Thailand

Zika virus has been circulating in Thailand since 2002 through continuous but likely low-level circulation. Here, we describe an infection in a pregnant woman who traveled to Thailand and South America during her pregnancy. By combining phylogenetic analysis with the patient's travel history and her pregnancy timeline, we confirmed that she likely got infected in Thailand at the end of 2021. This imported case of microcephaly highlights that Zika virus circulation in the country still constitutes a health risk, even in a year of lower incidence.

MAIN POINTS

Here we trace the origin of travel-acquired microcephaly to Thailand, providing additional evidence that pre-American lineages of Zika virus can harm the fetus and highlighting that Zika virus constitutes a health threat even in a year of lower incidence.

Molecular characterization and geographical distribution of Zika virus worldwide from 1947 to 2022

OBJECTIVES

We conducted molecular characterization, demonstrated the geographical distribution of Zika virus (ZIKV) circulating worldwide from 1947 to 2022 and explored the potential genetic recombination site in the Thailand ZIKV genomes.

METHODS

We constructed phylogenetic trees based on ZIKV coding sequences (CDS) and determined the geographical distribution of the representative viruses by genetic relationship and timeline. We determined genetic recombination among ZIKV and between ZIKV and other flaviviruses using similarity plot and bootscan analyzes, together with the phylogeny encompassing the CDS and eight subgenomic regions.

RESULTS

The phylogenetic trees comprising 717 CDS showed two distinct African and Asian lineages. ZIKV in the African lineage formed two sublineages, and ZIKV in the Asian lineage diversified into the Asian and American sublineages. The 1966 Malaysian isolate was designated the prototype of the Asian sublineage and formed a node of only one member, while the newer viruses formed a distinct node. We detected no genetic recombination in the Thailand ZIKV.

CONCLUSION

Five Thailand isolates discovered in 2006 were the second oldest ZIKV after the Malaysian prototype. Our result suggested two independent routes of ZIKV spread from Southeast Asia to Micronesia in 2007 and French Polynesia in 2013 before further spreading to South American countries.

Genetic diversity and phylogenetic analyses of Asian lineage Zika virus whole genome sequences derived from Culex quinquefasciatus mosquitoes and urine of patients during the 2020 epidemic in Thailand

Zika virus (ZIKV), a mosquito-borne flavivirus, has been continually emerging and re-emerging since 2010, with sporadic cases reported annually in Thailand, peaking at over 1000 confirmed positive cases in 2016. Leveraging high-throughput sequencing technologies, specifically whole genome sequencing (WGS), has facilitated rapid pathogen genome sequencing. In this study, we used multiplex amplicon sequencing on the Illumina Miseq instrument to describe ZIKV WGS. Six ZIKV WGS were derived from three samples of field-caught Culex quinquefasciatus mosquitoes (two males and one female) and three urine samples collected from patients in three different provinces of Thailand. Additionally, successful isolation of a ZIKV isolate occurred from a female Cx. quinquefasciatus. The WGS analysis revealed a correlation between the 2020 outbreak and the acquisition of five amino acid changes in the Asian lineage ZIKV strains from Thailand (2006), Cambodia (2010 and 2019), and the Philippines (2012). These changes, including C-T106A, prM-V1A, E-V473M, NS1-A188V, and NS5-M872V, were identified in all seven WGS, previously linked to significantly higher mortality rates. Furthermore, phylogenetic analysis indicated that the seven ZIKV sequences belonged to the Asian lineage. Notably, the genomic region of the E gene showed the highest nucleotide diversity (0.7-1.3%). This data holds significance in informing the development of molecular tools that enhance our understanding of virus patterns and evolution. Moreover, it may identify targets for improved methods to prevent and control future ZIKV outbreaks.

Detection of anti-premembrane antibody as a specific marker of four flavivirus serocomplexes and its application to serosurveillance in endemic regions

In the past few decades, several emerging/re-emerging mosquito-borne flaviviruses have resulted in disease outbreaks of public health concern in the tropics and subtropics. Due to cross-reactivities of antibodies recognizing the envelope protein of different flaviviruses, serosurveillance remains a challenge. Previously we reported that anti-premembrane (prM) antibody can discriminate between three flavivirus infections by Western blot analysis. In this study, we aimed to develop a serological assay that can discriminate infection or exposure with flaviviruses from four serocomplexes, including dengue (DENV), Zika (ZIKV), West Nile (WNV) and yellow fever (YFV) viruses, and explore its application for serosurveillance in flavivirus-endemic countries. We employed Western blot analysis including antigens of six flaviviruses (DENV1, 2 and 4, WNV, ZIKV and YFV) from four serocomplexes. We tested serum samples from YF-17D vaccinees, and from DENV, ZIKV and WNV panels that had been confirmed by RT-PCR or by neutralization assays. The overall sensitivity/specificity of anti-prM antibodies for DENV, ZIKV, WNV, and YFV infections/exposure were 91.7%/96.4%, 91.7%/99.2%, 88.9%/98.3%, and 91.3%/92.5%, respectively. When testing 48 samples from Brazil, we identified multiple flavivirus infections/exposure including DENV and ZIKV, DENV and YFV, and DENV, ZIKV and YFV. When testing 50 samples from the Philippines, we detected DENV, ZIKV, and DENV and ZIKV infections with a ZIKV seroprevalence rate of 10%, which was consistent with reports of low-level circulation of ZIKV in Asia. Together, these findings suggest that anti-prM antibody is a flavivirus serocomplex-specific marker and can be employed to delineate four flavivirus infections/exposure in regions where multiple flaviviruses co-circulate.

Seroprevalence of Dengue, Chikungunya and Zika at the epicenter of the congenital microcephaly epidemic in Northeast Brazil: A population-based survey

BACKGROUND

The four Dengue viruses (DENV) serotypes were re-introduced in Brazil's Northeast region in a couple of decades, between 1980's and 2010's, where the DENV1 was the first detected serotype and DENV4 the latest. Zika (ZIKV) and Chikungunya (CHIKV) viruses were introduced in Recife around 2014 and led to large outbreaks in 2015 and 2016, respectively. However, the true extent of the ZIKV and CHIKV outbreaks, as well as the risk factors associated with exposure to these viruses remain vague.

METHODS

We conducted a stratified multistage household serosurvey among residents aged between 5 and 65 years in the city of Recife, Northeast Brazil, from August 2018 to February 2019. The city neighborhoods were stratified and divided into high, intermediate, and low socioeconomic strata (SES). Previous ZIKV, DENV and CHIKV infections were detected by IgG-based enzyme linked immunosorbent assays (ELISA). Recent ZIKV and CHIKV infections were assessed through IgG3 and IgM ELISA, respectively. Design-adjusted seroprevalence were estimated by age group, sex, and SES. The ZIKV seroprevalence was adjusted to account for the cross-reactivity with dengue. Individual and household-related risk factors were analyzed through regression models to calculate the force of infection. Odds Ratio (OR) were estimated as measure of effect.

PRINCIPAL FINDINGS

A total of 2,070 residents' samples were collected and analyzed. The force of viral infection for high SES were lower as compared to low and intermediate SES. DENV seroprevalence was 88.7% (CI95%:87.0-90.4), and ranged from 81.2% (CI95%:76.9-85.6) in the high SES to 90.7% (CI95%:88.3-93.2) in the low SES. The overall adjusted ZIKV seroprevalence was 34.6% (CI95%:20.0-50.9), and ranged from 47.4% (CI95%:31.8-61.5) in the low SES to 23.4% (CI95%:12.2-33.8) in the high SES. The overall CHIKV seroprevalence was 35.7% (CI95%:32.6-38.9), and ranged from 38.6% (CI95%:33.6-43.6) in the low SES to 22.3% (CI95%:15.8-28.8) in the high SES. Surprisingly, ZIKV seroprevalence rapidly increased with age in the low and intermediate SES, while exhibited only a small increase with age in high SES. CHIKV seroprevalence according to age was stable in all SES. The prevalence of serological markers of ZIKV and CHIKV recent infections were 1.5% (CI95%:0.1-3.7) and 3.5% (CI95%:2.7-4.2), respectively.

CONCLUSIONS

Our results confirmed continued DENV transmission and intense ZIKV and CHIKV transmission during the 2015/2016 epidemics followed by ongoing low-level transmission. The study also highlights that a significant proportion of the population is still susceptible to be infected by ZIKV and CHIKV. The reasons underlying a ceasing of the ZIKV epidemic in 2017/18 and the impact of antibody decay in susceptibility to future DENV and ZIKV infections may be related to the interplay between disease transmission mechanism and actual exposure in the different SES.

Serological Evidence of Zika virus Circulation with Dengue and Chikungunya Infections in Sri Lanka from 2017

Introduction

Arbovirus diseases remain a public health threat in Sri Lanka. Dengue is endemic and two outbreaks of chikungunya infections have been reported. There is limited data on Zika virus (ZIKV) infections in Sri Lanka, and this could be due to a lack of comprehensive ZIKV surveillance. Our aim was to determine the presence of antibodies to dengue, chikungunya, and Zika infections in adults from a suburban population in Sri Lanka.

Methods

A total of 149 healthy adult volunteers over 18 years of age (mean age: 43±14 years, males - 43%), with no prior diagnosed arboviral infections and no history of overseas travel, participated in the study. ELISA and neutralization assays were carried out to detect past dengue, chikungunya, or Zika infections.

Results

A total of 94.6% (141/149) of the participants demonstrated dengue IgG antibodies, 37.5% (56/149) were positive for chikungunya IgG, and 5.3% (8/149) were positive for anti-ZIKV IgG antibodies. Neutralization assays confirmed ZIKV-specific antibodies in 6.7% (10/149), when 40/149 of the participating population were tested.

Conclusion

This clearly demonstrated past ZIKV infections in this population. In addition, this study indicates that >90% of individuals had asymptomatic dengue but no serious symptoms. These results provide a cross-sectional view on the DENV, ZIKV, and CHIKV epidemic status and demonstrate a need for the implementation of enhanced surveillance and more effective measures against the spread of these arbovirus diseases.

Zika virus infection in European travellers returning from Thailand in 2022: A GeoSentinel case series

Zika virus is a mosquito-borne flavivirus which caused major epidemics in the Pacific and the Americas between 2013 and 2015. International travellers have previously acted as a sentinel population for Zika virus transmission in endemic areas, where local transmission may be incompletely captured by local surveillance systems. We report five recent European travellers returning from Thailand with Zika virus infection, highlighting the risk of ongoing endemic transmission in this popular tourist destination.

Aedes aegypti and Aedes albopictus (Diptera: Culicidae) ecology, biology, behaviour, and implications on arbovirus transmission in Thailand: Review

Aedes aegypti and Aedes albopictus (Aedes) transmit highly pathogenic viruses such as dengue, chikungunya, yellow fever, and Zika which can cause life-threatening diseases in humans. They are the most important vectors of arboviruses in Thailand. Their vectorial capacity (VC) is highly complex mainly due to the interplay between biotic and abiotic factors that vary in time and space. A literature survey was conducted to collate and discuss recent research regarding the influence of Aedes vector biology, behaviour, and ecology on arbovirus transmission in Thailand. The survey followed guidelines of preferred reporting items of systematic reviews and meta-analyses (PRISMA). All fields, keyword search was conducted in the Web of Science database for the period of 2000-2021. The search yielded 821 records on Ae. aegypti and 293 records on Aedes albopictus, of which 77 were selected for discussion. Genomic studies showed that there is a high genetic variation in Aedes albopictus whereas Ae. aegypti generally shows low genetic variation. Along with genetically unstable arboviruses, the interaction between Aedes and arboviruses is largely regulated by genomic events such as genetic mutations and immune response protein factors. Temperature and precipitation are the major climatic events driving arbovirus transmission. Human exposure risk factors are mainly due to multiple feeding patterns, including endophagy by Aedes albopictus and zoophagic behaviour of Ae. aegypti as well as diverse human-associated breeding sites. Integration of the One Health approach in control interventions is a priority with a rigorous focus on Aedes-arbovirus surveillance as a complementary strategy.

Persistence of Immunogenicity of a Purified Inactivated Zika Virus Vaccine Candidate in Healthy Adults: 2 Years of Follow-up Compared With Natural Infection

BACKGROUND

We report 2-year persistence of immune response to Takeda's prophylactic purified formalin-inactivated whole Zika virus vaccine candidate (TAK-426) compared with that observed after natural infection.

METHODS

A randomized, observer-blind, placebo-controlled, dose-selection, phase 1 trial was conducted in 18-49-year-old adults at 9 centers (7 in the United States, 2 in Puerto Rico) from 13 November 2017 to 24 November 2020. Primary objectives were safety, tolerability, and immunogenicity of 3 increasing doses of TAK-426 administered as 2 doses 28 days apart to flavivirus (FV)-naive and FV-primed adults. Here, we report on safety and persistence of immunity up to 2 years after primary vaccination with 10-μg TAK-426, the highest dose, and compare neutralizing antibody responses with those observed after natural infection.

RESULTS

TAK-426 at 10-μg had an acceptable safety profile in FV-naive and FV-primed adults up to 24 months after dose 2. Seropositivity for neutralizing antibodies was 100% at 1 year, and 93.8% and 76.2% at 2 years in FV-naive and FV-primed groups, respectively. TAK-426 responses were comparable in magnitude and kinetics with those elicited by natural Zika virus infection.

CONCLUSIONS

These results support the further clinical development of TAK-426 for both FV-naive and FV-primed populations.

CLINICAL TRIALS REGISTRATION

NCT03343626.

Zika virus leads to olfactory disorders in mice by targeting olfactory ensheathing cells

BACKGROUND

Zika virus (ZIKV) is an emerging arbovirus of the genus flavivirus that is associated with congenital Zika syndrome (CZS) in newborns. A wide range of clinical symptoms including intellectual disability, speech delay, coordination or movement problems, and hearing and vision loss, have been well documented in children with CZS. However, whether ZIKV can invade the olfactory system and lead to post-viral olfactory dysfunction (PVOD) remains unknown.

METHODS

We investigated the susceptibility and biological responses of the olfactory system to ZIKV infection using mouse models and human olfactory organoids derived from patient olfactory mucosa.

FINDINGS

We demonstrate that neonatal mice infected with ZIKV suffer from transient olfactory dysfunction when they reach to puberty. Moreover, ZIKV mainly targets olfactory ensheathing cells (OECs) and exhibits broad cellular tropism colocalizing with small populations of mature/immature olfactory sensory neurons (mOSNs/iOSNs), sustentacular cells and horizontal basal cells in the olfactory mucosa (OM) of immunodeficient AG6 mice. ZIKV infection induces strong antiviral immune responses in both the olfactory mucosa and olfactory bulb tissues, resulting in the upregulation of proinflammatory cytokines/chemokines and genes related to the antiviral response. Histopathology and transcriptomic analysis showed typical tissue damage in the olfactory system. Finally, by using an air-liquid culture system, we showed that ZIKV mainly targets sustentacular cells and OECs and support robust ZIKV replication.

INTERPRETATION

Our results demonstrate that olfactory system represents as significant target for ZIKV infection, and that PVOD may be neglected in CZS patients.

FUNDING

Stated in the acknowledgment.

Molecular mechanism of ATP and RNA binding to Zika virus NS3 helicase and identification of repurposed drugs using molecular dynamics simulations

Congenital Zika virus syndrome has caused a public health emergency of international concern. So far, there are no drugs available to prevent or treat the infection caused by Zika virus. The Zika virus NS3 helicase is a potential protein target for drug discovery due to its vital role in viral genome replication. NS3 helicase unwinds the viral RNA to enable the reproduction of the viral genome by the NS5 protein. NS3 helicase has two crucial binding sites; the ATP binding site and the RNA binding site. We used molecular docking and molecular dynamics (MD) simulations to study the structural behavior of Zika virus NS3 helicase in its apo form and in the presence of ATP, single-stranded RNA, and both ATP-RNA to understand their potential implications in NS3 helicase activity. Further, we have carried out virtual screening of FDA approved drugs, followed by molecular docking to identify the ATP-competitive hit molecules as probable Zika virus NS3 helicase inhibitors. The MD simulations trajectories were analyzed using normal mode analysis and principal component analysis that reveals fluctuations in the R-loop. These findings aid in understanding the molecular mechanisms of the simultaneous binding of ATP and RNA, and guide the design and discovery of new inhibitors of the Zika virus NS3 helicase as a promising drug target to treat the Zika virus infection. Communicated by Ramaswamy H. Sarma.

Molecular surveillance of arboviruses circulation and co-infection during a large chikungunya virus outbreak in Thailand, October 2018 to February 2020

A large national outbreak of chikungunya virus (CHIKV) was recently reported in Thailand. While dengue virus (DENV) infection tends to occur year-round with an upsurge in the rainy season, Zika virus (ZIKV) also circulates in the country. The overlap in the distribution of these viruses increased the probability of co-infections during the heightened CHIKV activity. By examining 1806 patient serum samples submitted for CHIKV diagnostics from October 2018-February 2020 (511 CHIKV-negatives and 1295 CHIKV-positives), we used real-time reverse transcription-polymerase chain reaction to identify DENV and ZIKV individually. A total of 29 ZIKV and 36 DENV single-infections were identified. Interestingly, 13 co-infection cases were observed, of which 8 were CHIKV/DENV, 3 were CHIKV/ZIKV, and 2 were DENV/ZIKV. There were six DENV genotypes (13 DENV-1 genotype I, 10 DENV-2 Asian I, 10 DENV-2 Cosmopolitan, 6 DENV-3 genotype I, 2 DENV-3 genotype III, and 5 DENV-4 genotype I). Additionally, ZIKV strains identified in this study either clustered with strains previously circulating in Thailand and Singapore, or with strains previously reported in China, French Polynesia, and the Americas. Our findings reveal the co-infection and genetic diversity patterns of mosquito-borne viruses circulating in Thailand.

Arbovirus Seroprevalence Study in Bangphae District, Ratchaburi Province, Thailand: Comparison between ELISA and a Multiplex Rapid Diagnostic Test (Chembio DPP® ZCD IgG)

Arboviruses, particularly dengue virus (DENV), Zika virus (ZIKV), and Chikungunya virus (CHIKV), pose a growing threat to global public health. For disease burden estimation and disease control, seroprevalence studies are paramount. This study was performed to determine the prevalence of DENV, ZIKV, and CHIKV on healthy individuals aged from 1–55 years old in Bangphae district, Ratchaburi province, Thailand. Enzyme-linked immunosorbent assays (ELISAs) and rapid diagnostic tests (RDTs) were performed on archived samples from a dengue serological survey conducted from 2012–2015. All 2012 samples had been previously tested using an anti-DENV immunoglobulin (Ig)G ELISA, and 400 randomly selected samples stratified by age, sex, and residential area were assessed by an in-house anti-ZIKV IgG ELISA and a commercial anti-CHIKV IgG ELISA to determine virus-specific antibody levels. An RDT (Chembio DPP® ZCD IgM/IgG System) was also used to investigate the presence of antibodies against DENV, ZIKV, or CHIKV. The ELISA results indicate that the seroprevalences of DENV, ZIKV, and CHIKV were 84.3%, 58.0%, and 22.5%, respectively. The youngest age group had the lowest seroprevalence for all three arboviruses, and the seroprevalences for these viruses were progressively higher with increasing participant age. The DPP® IgG sensitivities, as compared with ELISAs, for DENV, ZIKV, and CHIKV were relatively low, only 43.92%, 25.86%, and 37.78%, respectively. The ELISA results indicate that 16% of the study population was seropositive for all three viruses. DENV had the highest seroprevalence. ZIKV and CHIKV were also circulating in Bangphae district, Ratchaburi province, Thailand. The DPP® ZCD rapid test is not sensitive enough for use in seroprevalence studies.

Development and evaluation of a visible reverse transcription-loop-mediated isothermal amplification (RT-LAMP) for the detection of Asian lineage ZIKV in field-caught mosquitoes

The Zika virus (ZIKV) infection is an emerging and re-emerging arbovirus infection that is transmitted to humans through the bite of infected mosquitoes. Early detection of ZIKV in mosquitoes is one of the prerequisite approaches for tracking the spread of the virus. Therefore, this study aims to develop and validate a visual reverse transcription-loop-mediated isothermal amplification (RT-LAMP) method called ZIKV-RT-LAMP, for detecting ZIKV in field collected mosquito samples from Thailand. A single-tube ZIKV-RT-LAMP assay was developed to detect Asian lineage ZIKV RNA. The detection limit and cross-reactivity of ZIKV were investigated. The hemi-nested RT-PCR (hn-RT-PCR) and the colorimetric LAMP kit (cLAMP kit) were performed as reference assays. The detection limit of the ZIKV-RT-LAMP assay was 10^-6 ffu/ml or pfu/ml, making it highly specific and 100 times more sensitive than the hn-RT-PCR and cLAMP kits. The ZIKV-RT-LAMP assay detected the Asian lineage of ZIKV RNA without cross-reactivity with other arthropod-borne viruses. The sensitivity and specificity of the ZIKV-RT-LAMP assay were 92.31% and 100%, respectively. The ZIKV-RT-LAMP is a simple, rapid, and inexpensive method for detecting ZIKV in field-caught mosquitos. In the future, extensive surveys of field-caught mosquito populations should be conducted. Early detection of ZIKV in field-caught mosquitoes provides for prompt and effective implementation of mosquito control strategies in endemic areas.

Zika vector competence data reveals risks of outbreaks: the contribution of the European ZIKAlliance project

First identified in 1947, Zika virus took roughly 70 years to cause a pandemic unusually associated with virus-induced brain damage in newborns. Zika virus is transmitted by mosquitoes, mainly Aedes aegypti, and secondarily, Aedes albopictus, both colonizing a large strip encompassing tropical and temperate regions. As part of the international project ZIKAlliance initiated in 2016, 50 mosquito populations from six species collected in 12 countries were experimentally infected with different Zika viruses. Here, we show that Ae. aegypti is mainly responsible for Zika virus transmission having the highest susceptibility to viral infections. Other species play a secondary role in transmission while Culex mosquitoes are largely non-susceptible. Zika strain is expected to significantly modulate transmission efficiency with African strains being more likely to cause an outbreak. As the distribution of Ae. aegypti will doubtless expand with climate change and without new marketed vaccines, all the ingredients are in place to relive a new pandemic of Zika.

Zika virus (ZIKV), the causative agent of virus-induced brain damage in newborns, is transmitted by mosquitoes, mainly Aedes aegypti, and secondarily, Aedes albopictus. Here, Obadia et al. characterize ZIKV vector competence of 50 mosquito populations from six species collected in 12 different countries to inform about epidemic risk. They find that African ZIKV strain shows higher transmission efficiency compared to American and Asian ZIKV strains and that Ae. aegypti mosquitoes have highest susceptibility to infections, while Culexmosquitoes are largely non-susceptible.

Etiology of acute febrile illnesses in Southern China: Findings from a two-year sentinel surveillance project, 2017-2019

BACKGROUND

Southern China is at risk for arborvirus disease transmission, including Zika virus and dengue. Patients often present to clinical care with non-specific acute febrile illnesses (AFI). To better describe the etiology of AFI, we implemented a two-year AFI surveillance project at five sentinel hospitals in Yunnan and Guangdong Provinces.

METHODS

Between June 2017 and August 2019, we enrolled patients between 2 and 65 years of age presenting at one sentinel hospital in Mengla County, Yunnan, and four in Jiangmen City, Guangdong, with symptoms of AFI (acute onset of fever ≥ 37.5°C within the past 7 days) without respiratory symptoms or diarrhea. Demographic, epidemiologic, and clinical information was obtained and entered into a web-based AFI surveillance database. A custom TaqMan Array card (TAC) was used to test patients' whole blood specimens for 27 different pathogens using real-time polymerase chain reaction assays.

RESULTS

During the two-year project period, 836 patients were enrolled; 443 patients from Mengla County and 393 patients from Jiangmen City. The median age was 33 years [range: 2-65], and most were hospitalized [641, 77%]. Of 796 patients with valid TAC results, 341 (43%) were positive for at least one of the 10 unique pathogens detected. This included 205 (26%) patients positive for dengue virus, 60 (8%) for Orientia tsutsugamushi, and 42 (5%) for Coxiella burnetii. Ten patients (1%) in Jiangmen City tested positive for malaria, 8 of whom reported recent travel outside of China. TAC results were negative for 455 (57%) patients. None of the patients had a positive TAC detection for Zika virus.

CONCLUSIONS

The project detected variability in the etiology of AFI in Southern China and highlighted the importance of differential diagnosis. Dengue, O. tsutsugamushi, and C. burnetii were the most frequently identified pathogens among enrolled AFI patients. As a non-notifiable disease, the frequent detection of C. burnetii is noteworthy and warrants additional investigation. The project provided a framework for routine surveillance for persons presenting with AFI.

Assessing the role of multiple mechanisms increasing the age of dengue cases in Thailand

The age of reported dengue hemorrhagic fever (DHF) cases, the severe form of dengue infections, has been increasing in Thailand for four decades. Factors underlying this shift remain poorly understood, challenging public health planning. Here, we found aging of the population and its effect on the hazard of transmission to be the dominant contributors, with temporal changes in surveillance practices playing a lesser role. With ongoing population aging, we expect a continuing shift of DHF toward older individuals, heightening the chance of clinical complications with comorbidities. With most other highly endemic countries facing similar shifts in age structure, the pattern is expected to appear elsewhere. Awareness is needed to improve diagnosis and treatment.

The mean age of dengue hemorrhagic fever (DHF) cases increased considerably in Thailand from 8.1 to 24.3 y between 1981 and 2017 (mean annual increase of 0.45 y). Alternative proposed explanations for this trend, such as changes in surveillance practices, reduced mosquito–human contact, and shifts in population demographics, have different implications for global dengue epidemiology. To evaluate the contribution of each of these hypothesized mechanisms to the observed data, we developed 20 nested epidemiological models of dengue virus infection, allowing for variation over time in population demographics, infection hazards, and reporting rates. We also quantified the effect of removing or retaining each source of variation in simulations of the age trajectory. Shifts in the age structure of susceptibility explained 58% of the observed change in age. Adding heterogeneous reporting by age and reductions in per-serotype infection hazard to models with shifts in susceptibility explained an additional 42%. Reductions in infection hazards were mostly driven by changes in the number of infectious individuals at any time (another consequence of shifting age demographics) rather than changes in the transmissibility of individual infections. We conclude that the demographic transition drives the overwhelming majority of the observed change as it changes both the age structure of susceptibility and the number of infectious individuals. With the projected Thai population age structure, our results suggest a continuing increase in age of DHF cases, shifting the burden toward individuals with more comorbidity. These insights into dengue epidemiology may be relevant to many regions of the globe currently undergoing comparable changes in population demographics.

The distinguishing NS5-M114V mutation in American Zika virus isolates has negligible impacts on virus replication and transmission potential

During 2015–2016, outbreaks of Zika virus (ZIKV) occurred in Southeast Asia and the Americas. Most ZIKV infections in humans are asymptomatic, while clinical manifestation is usually a self-limiting febrile disease with maculopapular rash. However, ZIKV is capable of inducing a range of severe neurological complications collectively described as congenital Zika syndrome (CZS). Notably, the scale and magnitude of outbreaks in Southeast Asia were significantly smaller compared to those in the Americas. Sequence comparison between epidemic-associated ZIKV strains from Southeast Asia with those from the Americas revealed a methionine to valine substitution at residue position 114 of the NS5 protein (NS5-M114V) in all the American isolates. Using an American isolate of ZIKV (Natal), we investigated the impact of NS5-M114V mutation on virus replication in cells, virulence in interferon (IFN) α/β receptor knockout (Ifnar^-/-) mice, as well as replication and transmission potential in Aedes aegypti mosquitoes. We demonstrated that NS5-M114V mutation had insignificant effect on ZIKV replication efficiency in cells, its ability to degrade STAT2, and virulence in vivo, albeit viremia was slightly prolonged in mice. Furthermore, NS5-M114V mutation decreased mosquito infection and dissemination rates but had no effect on virus secretion into the saliva. Taken together, our findings support the notion that NS5-M114V mutation is unlikely to be a major determinant for virus replication and transmission potential.

Zika virus (ZIKV) emerged to cause outbreaks in Southeast Asia and the Americas during 2015–2016. However, the scale of outbreaks in Southeast Asia were significantly smaller compared to epidemic in the Americas. A methionine to valine amino acid mutation at residue position 114 of the NS5 protein (NS5-M114V) is hypothesized to influence the epidemic outcomes of ZIKV, which led to the large-scale epidemic that occurred in the Americas. By analyzing infection of mammalian and mosquito cells, IFNα/β receptor knockout (Ifnar^-/-) mice and Aedes aegypti mosquitoes with engineered ZIKV isolates containing either methionine or valine at residue position 114 of the NS5 protein, we demonstrated that the NS5-M114V mutation did not affect virus replication efficiency and STAT2 degradation in cells, virulence in mice, or virus secretion into the mosquito saliva. The NS5-M114V mutation slightly prolonged viremia in Ifnar^-/- mice and reduced mosquito infection rate. Collectively, our findings suggest that the NS5-M114V mutation is unlikely to have significantly influenced the ZIKV epidemic in the Americas.

Capeding M, Padilla CD, Sasmono RT, Hafalla JCR, Hibberd ML. Combining rapid diagnostic tests to estimate primary and post-primary dengue immune status at the point of care

BACKGROUND

Characterising dengue virus (DENV) infection history at the point of care is challenging as it relies on intensive laboratory techniques. We investigated how combining different rapid diagnostic tests (RDTs) can be used to accurately determine the primary and post-primary DENV immune status of reporting patients during diagnosis.

METHODS AND FINDINGS

Serum from cross-sectional surveys of acute suspected dengue patients in Indonesia (N:200) and Vietnam (N: 1,217) were assayed using dengue laboratory assays and RDTs. Using logistic regression modelling, we determined the probability of being DENV NS1, IgM and IgG RDT positive according to corresponding laboratory viremia, IgM and IgG ELISA metrics. Laboratory test thresholds for RDT positivity/negativity were calculated using Youden's J index and were utilized to estimate the RDT outcomes in patients from the Philippines, where only data for viremia, IgM and IgG were available (N:28,326). Lastly, the probabilities of being primary or post-primary according to every outcome using all RDTs, by day of fever, were calculated. Combining NS1, IgM and IgG RDTs captured 94.6% (52/55) and 95.4% (104/109) of laboratory-confirmed primary and post-primary DENV cases, respectively, during the first 5 days of fever. Laboratory test predicted, and actual, RDT outcomes had high agreement (79.5% (159/200)). Among patients from the Philippines, different combinations of estimated RDT outcomes were indicative of post-primary and primary immune status. Overall, IgG RDT positive results were confirmatory of post-primary infections. In contrast, IgG RDT negative results were suggestive of both primary and post-primary infections on days 1-2 of fever, yet were confirmatory of primary infections on days 3-5 of fever.

CONCLUSION

We demonstrate how the primary and post-primary DENV immune status of reporting patients can be estimated at the point of care by combining NS1, IgM and IgG RDTs and considering the days since symptoms onset. This framework has the potential to strengthen surveillance operations and dengue prognosis, particularly in low resource settings.

Excito-repellency of Myristica fragrans Houtt. and Curcuma longa L. extracts from Southern Thailand against Aedes aegypti (L.)

The development of local plant extracts as a mosquito repellent is environmentally safe, inexpensive, and easily accessible for residents. In this study, three extracts from two local plants, Myristica fragrans Houtt. (flesh and mace) and Curcuma longa L. (rhizome) from southern Thailand, were investigated for their inherent repellent activity using the excito-repellency (ER) assay system against insectary-colonized Aedes aegypti (L.) (Diptera: Culicidae). The escape responses of mosquitoes exposed to concentrations of 0.5% to 5.0% (w/v) were measured to determine the contact irritant and non-contact repellent properties of each extract. Both the flesh and mace extracts of M. fragrans had relatively limited contact irritants (28.1% and 34.6% escape) and non-contact repellent (16.7% and 18.3% escape) activities against Ae. aegypti, respectively. The C. longa rhizome extract produced higher escape responses in the non-contact (42.6% escape) and contact (41.4% escape) trials at concentrations of 5.0% and 1.0%, respectively. GC-MS analysis found diethyl malate (56.5%) and elemicin (11.7%) to be the main components of the flesh and mace extracts, respectively, while ar-turmerone (24.6%), β-turmerone (15.2%), α-turmerone (10.5%) were the primary constituents of the rhizome extract. Overall, our results indicate that both M. fragrans extracts primarily caused Ae. aegypti escape through contact irritation. For C. longa, lower concentrations (0.5% and 1.0%) exhibited contact irritancy, but higher concentrations (2.5% and 5.0%) exhibited non-contact repellency against Ae. aegypti. Although they had limited efficacy, further experiments (e.g., mixing with other plant-based compounds) could enhance the ER of both local plant extracts. Additional evaluation of these extracts against other mosquito species and the ER of their chemical components, either alone or in combination, would also be beneficial for the development of green repellents. Our findings emphasize the possibility of utilizing plant-based mosquito repellent as an alternative personal protection method for future mosquito control programs.

Discovering disease-causing pathogens in resource-scarce Southeast Asia using a global metagenomic pathogen monitoring system

SignificanceMetagenomic pathogen sequencing offers an unbiased approach to characterizing febrile illness. In resource-scarce settings with high biodiversity, it is critical to identify disease-causing pathogens in order to understand burden and to prioritize efforts for control. Here, metagenomic next-generation sequencing (mNGS) characterization of the pathogen landscape in Cambodia revealed diverse vector-borne and zoonotic pathogens irrespective of age and gender as risk factors. Identification of key pathogens led to changes in national program surveillance. This study is a "real world" example of the use of mNGS surveillance of febrile individuals, executed in-country, to identify outbreaks of vector-borne, zoonotic, and other emerging pathogens in a resource-scarce setting.

Zika Virus Immunoglobulin G Seroprevalence among Young Adults Living with HIV or without HIV in Thailand from 1997 to 2017

Zika virus (ZIKV) epidemiological data in Thailand are limited. We assessed ZIKV IgG seroprevalence among young adults during 1997–2017 and determined factors associated with ZIKV IgG seropositivity. This retrospective laboratory study included randomly selected subjects aged 18–25 years participating in large clinical studies conducted in Thailand during 1997–2017. Stored plasma samples were analyzed for ZIKV IgG using an ELISA test (Anti-Zika Virus IgG, EUROIMMUN, Lübeck, Germany). Sociodemographic, clinical and laboratory data were used in univariable and multivariable analyses to identify factors associated with ZIKV IgG positivity. Of the 1648 subjects included, 1259 were pregnant women, 844 were living with HIV and 111 were living with HBV. ZIKV IgG seroprevalence was similar among the HIV-infected and -uninfected pregnant women (22.8% vs. 25.8%, p-value = 0.335) and was overall stable among the pregnant women, with a 25.2% prevalence. Factors independently associated with ZIKV IgG positivity included an age of 23–25 years as compared to 18–20 years, an HIV RNA load below 3.88 log₁₀ copies/mL and birth in regions outside northern Thailand. Our study shows that a large proportion of the population in Thailand probably remains susceptible to ZIKV infection, which could be the ground for future outbreaks. Continued surveillance of ZIKV spread in Thailand is needed to inform public health policies.

The epitope arrangement on flavivirus particles contributes to Mab C10's extraordinary neutralization breadth across Zika and dengue viruses

The human monoclonal antibody C10 exhibits extraordinary cross-reactivity, potently neutralizing Zika virus (ZIKV) and the four serotypes of dengue virus (DENV1-DENV4). Here we describe a comparative structure-function analysis of C10 bound to the envelope (E) protein dimers of the five viruses it neutralizes. We demonstrate that the C10 Fab has high affinity for ZIKV and DENV1 but not for DENV2, DENV3, and DENV4. We further show that the C10 interaction with the latter viruses requires an E protein conformational landscape that limits binding to only one of the three independent epitopes per virion. This limited affinity is nevertheless counterbalanced by the particle's icosahedral organization, which allows two different dimers to be reached by both Fab arms of a C10 immunoglobulin. The epitopes' geometric distribution thus confers C10 its exceptional neutralization breadth. Our results highlight the importance not only of paratope/epitope complementarity but also the topological distribution for epitope-focused vaccine design.

Novel Assay to Measure Seroprevalence of Zika Virus in the Philippines

Zika virus (ZIKV) is a member of the Flaviviridae family, which includes other clinically notable viruses such as the 4 dengue virus serotypes (DENV-1-4). Distinguishing DENVs from ZIKV using the established serologic assays widely used for monitoring DENV transmission is difficult because of antibody cross-reactivity between these closely related flaviviruses. We describe a modified and improved recombinant envelope domain III-based serologic assay for detecting ZIKV type-specific antibodies in regions with endemic DENV transmission. When the assay was used to measure ZIKV seroprevalence in 2017 among children 9-14 years of age living in a region of the Philippines with endemic DENV transmission, we observed a ZIKV seroprevalence of 18%. Investigators should consider using the ZIKV envelope domain III-based assay, which is simple and readily adaptable for use in standard clinical and public health laboratories, to assess ZIKV seroprevalence in areas with endemic DENV transmission.

Seroprevalence of Zika virus in pregnant women from central Thailand

Zika virus (ZKV) infection in a pregnant woman, especially during the first trimester, often results in congenital anomalies. However, the pathogenic mechanism is unknown and one-third of ZKV infected pregnancies are asymptomatic. Neutralizing antibodies against ZKV has been reported in 70% of Thai adults, but the prevalence among pregnant women is unknown. Currently, vaccines and specific treatments for ZKV are under development. A better understanding of the immune status of pregnant women will increase the success of effective prevention guidelines. The prevalence of ZKV infection in pregnant women in antenatal care clinics was investigated during the rainy season from May to October 2019 at Siriraj Hospital, Bangkok, Thailand. We recruited 650 pregnant women (39.42% first, 52.26% second and 7.36% third trimester) and found that 30.77% had ZKV-specific IgG, and 39.81% had neutralizing antibodies (nAb) against ZKV (titer ≥10). Specific and neutralizing antibody levels varied by maternal age, trimester, and month. We further characterized the cross-reaction between ZKV and the four Dengue virus (DENV) serotypes by focused reduction neutralization test (FRNT) and found that cross-reactions were common. In conclusion, about 60% of pregnant women who living in central Thailand may be at risk of ZKV infection due to the absence of neutralizing antibodies against ZKV. The functions of cross-reactive antibodies between related viral genotypes require further study. These findings have implications for health care monitoring in pregnant women including determining the risk of ZKV infection, assisting the development of a flavivirus vaccine, and informing the development of preventative health policies.

Incidence of Zika Virus Infection from a Dengue Epidemiological Study of Children in Ratchaburi Province, Thailand

Zika virus (ZIKV) is the mosquito-transmitted virus that the WHO declared a Public Health Emergency of International Concern in 2016 due to the consequence of microcephaly from infected pregnancies. The incidence of Zika infection has been unclear in many countries because most infected people have nonspecific febrile illnesses. This study’s aim is to investigate the incidence of symptomatic Zika virus infections from the archived samples of a dengue cohort study of children in central Thailand from 2006 to 2009. We performed Zika NS1 immunoglobulin (Ig)G enzyme-linked immunosorbent assay (ELISA) screening to identify symptomatic Zika infections in paired acute/convalescent serum samples. Symptomatic Zika infections were confirmed by reverse transcription polymerase chain reactions (RT-PCR) of acute serum samples. The comparison of the Zika NS1 IgG ELISA results between acute and convalescent samples showed 290/955 (30.4%) seropositive cases. Zika RT-PCR results were positive in 28 febrile cases (15 females, 13 males). Zika RT-PCR showed that symptomatic Zika infection occurred in children aged 4–11 years in Ratchaburi province, Thailand (2007–2009, first case in April 2007), and the symptomatic Zika:dengue infection ratio was 28 Zika:394 dengue (1:14). Phylogenetic analysis showed that all Zika viruses were of Asian lineage. Zika NS1 IgG ELISA identified Zika-infected patients and showed a low Zika:dengue ratio.

Zika Prevention Behaviors Among Women of Reproductive Age in Puerto Rico, 2016

INTRODUCTION

Zika virus is primarily transmitted through mosquito bites. Because Zika virus infection during pregnancy can cause serious birth defects, reproductive-aged women need protection from Zika virus infection. This report describes Zika virus prevention behaviors among women aged 18-49 years and assesses whether pregnancy status and healthcare provider counseling increases Zika virus prevention behaviors.

METHODS

A population-based cell phone survey of women aged 18-49 years living in Puerto Rico was conducted in July-November 2016. Data were analyzed in 2018-2019. Prevalence estimates and 95% CIs were calculated for Zika virus prevention behaviors. Adjusted prevalence ratios were estimated to examine the association of pregnancy status with healthcare provider counseling on Zika virus prevention behaviors, controlling for age, education, and health insurance status.

RESULTS

Most women reported using screens on open doors/windows (87.7%) and eliminating standing water in/around their homes (92.3%). Other Zika virus prevention behaviors were less common (<33%). In adjusted analysis, pregnant women were more likely than women not at risk for unintended pregnancy to report using mosquito repellent every/most days (adjusted prevalence ratio=1.44, 95% CI=1.13, 1.85). Healthcare provider counseling was associated with receiving professional spraying/larvicide treatment (adjusted prevalence ratio=1.42, 95% CI=1.17, 1.74), sleeping under a bed net (adjusted prevalence ratio=2.37, 95% CI=1.33, 4.24), using mosquito repellent (adjusted prevalence ratio=1.57, 95% CI=1.40, 1.77), and wearing long sleeves/pants (adjusted prevalence ratio=1.32, 95% CI=1.12, 1.55).

CONCLUSIONS

Receipt of healthcare provider counseling was more consistently associated with Zika virus prevention behaviors than pregnancy status. Healthcare provider counseling is an important strategy for increasing the uptake of Zika virus prevention behaviors among women aged 18-49 years.

Standardization and Evaluation of an Anti-ZIKV IgM ELISA Assay for the Serological Diagnosis of Zika Virus Infection

Here, we describe the development of the in-house anti-Zika virus (ZIKV) IgM antibody capture ELISA (in-house ZIKV IgM ELISA) for the detection and diagnosis of acute ZIKV infections. We compared the in-house ZIKV IgM ELISA assay performance against two commercial kits, Euroimmun ZIKV IgM and InBios 2.0 ZIKV IgM ELISA. We tested the assays' ability to detect anti-ZIKV IgM using a well-defined serum sample panel. This panel included 80 ZIKV negative samples (20 negative, 20 found to be primary dengue virus [DENV][ infections, 20 secondary DENV infections, and 20 Japanese encephalitis virus [JEV] infections) and 67 ZIKV reverse transcriptase-polymerase chain reaction-positive acute serum samples. The OD values were calculated to enzyme immunoassay (EIA) unts by comparing them to weak positive controls. The results demonstrated the high sensitivity (88.06%) and specificity (90.00%) of our in-house ZIKV IgM ELISA and its 89.12% overall percentage agreement. The kappa values were deemed to be within excellent range and comparable to the InBios ZIKV IgM ELISA. Some cross-reactivity was observed among secondary DENV and JEV samples, and to a much lower extent, among primary DENV samples. These data indicate that our in-house ZIKV IgM ELISA is a reliable assay for the detection of anti-ZIKV IgM antibodies in serum.

Zika virus isolation, propagation, and quantification using multiple methods

Zika virus (ZIKV) was isolated from the archival urine, serum, and autopsy specimens by intrathoracic inoculation of Toxorhynchitis splendens and followed by three blind sub-passaging in C6/36 mosquito cells. The virus isolates were identified using an immunofluorescence assay and real-time reverse transcription-polymerase chain reaction (real-time RT-PCR). This study analyzed 11 ZIKV isolates. One isolate (0.6%) was obtained from 171 urine samples, eight (8.7%) from 92 serum samples and two from tissues of an abortive fetus. After propagation in C6/36 cells, ZIKV was titrated by plaque and focus forming unit (FFU) assays in Vero cell monolayers, and viral genomes were determined via real-time and digital RT-PCR. Plaque and FFU assay quantitations were comparable, with the amount of infectious viruses averaging 106-107 PFU or FFU/ml. Real-time RT-PCR semi-quantified the viral genome numbers, with Ct values varying from 12 to 14. Digital RT-PCR, which precisely determines the numbers of the viral genomes, consistently averaged 10-100 times higher than the number of infectious units. There was good correlation between the results of these titration methods. Therefore, the selection of a method should be based on the objectives of each research studies.

Serological Evidence of Widespread Zika Transmission across the Philippines

Zika virus (ZIKV) exposure across flavivirus-endemic countries, including the Philippines, remains largely unknown despite sporadic case reporting and environmental suitability for transmission. Using laboratory surveillance data from 2016, 997 serum samples were randomly selected from suspected dengue (DENV) case reports across the Philippines and assayed for serological markers of short-term (IgM) and long-term (IgG) ZIKV exposure. Using mixture models, we re-evaluated ZIKV IgM/G seroprevalence thresholds and used catalytic models to quantify the force of infection (attack rate, AR) from age-accumulated ZIKV exposure. While we observed extensive ZIKV/DENV IgG cross-reactivity, not all individuals with active DENV presented with elevated ZIKV IgG, and a proportion of dengue-negative cases (DENV IgG-) were ZIKV IgG-positive (14.3%, 9/63). We identified evidence of long-term, yet not short-term, ZIKV exposure across Philippine regions (ZIKV IgG+: 31.5%, 314/997) which was geographically uncorrelated with DENV exposure. In contrast to the DENV AR (12.7% (95%CI: 9.1-17.4%)), the ZIKV AR was lower (5.7% (95%CI: 3-11%)) across the country. Our results provide evidence of widespread ZIKV exposure across the Philippines and suggest the need for studies to identify ZIKV infection risk factors over time to better prepare for potential future outbreaks.

Lack of Association between Adverse Pregnancy Outcomes and Zika Antibodies among Pregnant Women in Thailand between 1997 and 2015

Data about Zika virus infection and adverse pregnancy outcomes in Southeast Asia are scarce. We conducted an unmatched case-control study of Zika virus (ZIKV) serology in pregnant women enrolled in human immunodeficiency virus (HIV) or hepatitis B virus (HBV) perinatal prevention trials between 1997 and 2015 in Thailand. Case and control groups included women with and without adverse pregnancy outcomes. Plasma samples collected during the last trimester of pregnancy were tested for ZIKV IgG/IgM and Dengue IgG/IgM (Euroimmun, AG, Germany). Case newborn plasma samples were tested for ZIKV IgM and ZIKV RNA (Viasure, Spain). The case group included women with stillbirth (n = 22) or whose infants had microcephaly (n = 4), a head circumference below the first percentile (n = 14), neurological disorders (n = 36), or had died within 10 days after birth (n = 11). No women in the case group were positive for ZIKV IgM, and none of their live-born neonates were positive for ZIKV IgM or ZIKV RNA. The overall ZIKV IgG prevalence was 29%, 24% in the case and 34% in the control groups (Fisher's exact test; p = 0.13), while the dengue IgG seroprevalence was 90%. Neither neonatal ZIKV infections nor ZIKV-related adverse pregnancy outcomes were observed in these women with HIV and/or HBV during the 18-year study period.