Zika Virus

How Did Zika Virus Emerge in the Pacific Islands and Latin America?

The unexpected emergence of Zika virus (ZIKV) in the Pacific Islands and Latin America and its association with congenital Zika virus syndrome (CZVS) (which includes microcephaly) and Guillain-Barré syndrome (GBS) have stimulated wide-ranging research. High densities of susceptible Aedes spp., immunologically naive human populations, global population growth with increased urbanization, and escalation of global transportation of humans and commercial goods carrying vectors and ZIKV undoubtedly enhanced the emergence of ZIKV. However, flavivirus mutations accumulate with time, increasing the likelihood that genetic viral differences are determinants of change in viral phenotype. Based on comparative ZIKV complete genome phylogenetic analyses and temporal estimates, we identify amino acid substitutions that may be associated with increased viral epidemicity, CZVS, and GBS. Reverse genetics, vector competence, and seroepidemiological studies will test our hypothesis that these amino acid substitutions are determinants of epidemic and neurotropic ZIKV emergence.

Zika virus infection or the future of infectious diseases

Zika virus belongs to the Flaviridae, an extended phylogenetic family containing dengue or yellow fever, viruses whose shared main vector are Aedes aegypti mosquitoes. The virus originally came from Central African simian reservoirs and, from there, expanded rapidly across the Pacific to South America. The disease is an example of exantematic fever usually mild. Mortality is very low and mainly limited to secondary Guillain-Barré or foetal microcephaly cases. Diagnostic confirmation requires a RT-PCR in blood up to the 5th day from the onset or in urine up to the 10-14th day. Specific IgM are identifiable from the 5th symptomatic day. Clinically, a suspected case should comply with: (a) a journey to epidemic areas; (b) a clinically compatible appearance with fever and skin rash, and (c) a generally normal blood count/basic biochemistry. There is some evidence that causally relates Zika virus infection with foetal microcephaly. While waiting for definitive data, all pregnant women coming from Central or South America should be tested for Zika virus.

Results of a Zika Virus (ZIKV) Immunoglobulin M-Specific Diagnostic Assay Are Highly Correlated With Detection of Neutralizing Anti-ZIKV Antibodies in Neonates With Congenital Disease

BACKGROUND

 Usually, immunoglobulin M (IgM) serologic analysis is not sufficiently specific to confirm Zika virus (ZIKV) infection. However, since IgM does not cross the placenta, it may be a good marker of infection in neonates.

METHODS

 We tested blood from 42 mothers and neonates with microcephaly and collected cerebrospinal fluid (CSF) specimens from 30 neonates. Molecular assays were performed for detection of ZIKV, dengue virus, and chikungunya virus; IgM enzyme-linked immunosorbent assays and plaque-reduction neutralization tests (PRNTs) were performed to detect ZIKV and dengue virus. No control neonates without microcephaly were evaluated.

RESULTS

 Among neonates, all 42 tested positive for ZIKV IgM: 38 of 42 serum specimens (90.5%) were positive, whereas 30 of 30 CSF specimens (100%) were positive. ZIKV IgM-specific ELISA ratios, calculated as the mean optical density (OD) of the test sample when reacted on viral antigen divided by the mean OD of the negative control when reacted with viral antigen, were higher in CSF specimens (median, 14.9 [range, 9.3-16.4]) than in serum (median, 8.9 [range, 2.1-20.6]; P = .0003). All ZIKV IgM-positive results among the neonates were confirmed by the detection of neutralizing antibodies. Mother/neonate pairs with primary ZIKV infection had neutralizing antibodies to ZIKV only, and mother/neonate pairs with ZIKV virus infection secondary to infection with another flavivirus had high titers of neutralizing antibodies to ZIKV. Among secondary infections, median titers in serum were 2072 (range, 232-12 980) for mothers and 2730 (range, 398-12 980) for neonates (P < .0001), and the median titer in CSF was 93 (range, 40-578) among neonates (P < .0001).

CONCLUSIONS

 Among neonates, detection of ZIKV IgM in serum is confirmatory of congenital ZIKV infection, and detection of ZIKV IgM in CSF is confirmatory of neurologic infection. Therefore, we recommend testing for ZIKV IgM in neonates suspected of having congenital ZIKV infection and performance of PRNTs in equivocal cases.

First detection of natural infection of Aedes aegypti with Zika virus in Brazil and throughout South America

Zika virus (ZIKV) has caused a major epidemic in Brazil and several other American countries. ZIKV is an arbovirus whose natural vectors during epidemics have been poorly determined. In this study, 1,683 mosquitoes collected in the vicinity of ZIKV suspected cases in Rio de Janeiro, Brazil, from June 2015 to May 2016 were screened for natural infection by using molecular methods. Three pools of Aedes aegypti were found with the ZIKV genome, one of which had only one male. This finding supports the occurrence of vertical and/or venereal transmission of ZIKV in Ae. aegypti in nature. None of the examined Ae. albopictus and Culex quinquefasciatus was positive. This is the first report of natural infection by ZIKV in mosquitoes in Brazil and other South American countries. So far, Ae. aegypti is the only confirmed vector of ZIKV during the ongoing Pan-American epidemics.

Zika virus: An emergent neuropathological agent

The emergence of Zika virus in the Americas has followed a pattern that is familiar from earlier epidemics of other viruses, where a new disease is introduced into a human population and then spreads rapidly with important public health consequences. In the case of Zika virus, an accumulating body of recent evidence implicates the virus in the etiology of serious pathologies of the human nervous system, that is, the occurrence of microcephaly in neonates and Guillain-Barré syndrome in adults. Zika virus is an arbovirus (arthropod-borne virus) and a member of the family Flaviviridae, genus Flavivirus. Zika virions are enveloped and icosahedral, and contain a nonsegmented, single-stranded, positive-sense RNA genome, which encodes 3 structural and 7 nonstructural proteins that are expressed as a single polyprotein that undergoes cleavage. Zika genomic RNA replicates in the cytoplasm of infected host cells. Zika virus was first detected in 1947 in the blood of a febrile monkey in Uganda's Zika Forest and in crushed suspensions of the Aedes mosquito, which is one of the vectors for Zika virus. The virus remained obscure, with a few human cases confined to Africa and Asia. There are two lineages of the Zika virus, African and Asian, with the Asian strain causing outbreaks in Micronesia in 2007 and French Polynesia in 2013-2014. From here, the virus spread to Brazil with the first report of autochthonous Zika transmission in the Americas in March 2015. The rapid advance of the virus in the Americas and its likely association with microcephaly and Guillain-Barré syndrome make Zika an urgent public health concern. Ann Neurol 2016;80:479-489.

Genetic Characterization of Spondweni and Zika Viruses and Susceptibility of Geographically Distinct Strains of Aedes aegypti, Aedes albopictus and Culex quinquefasciatus (Diptera: Culicidae) to Spondweni Virus

BACKGROUND

Zika virus (ZIKV) has extended its known geographic distribution to the New World and is now responsible for severe clinical complications in a subset of patients. While substantial genetic and vector susceptibility data exist for ZIKV, less is known for the closest related flavivirus, Spondweni virus (SPONV). Both ZIKV and SPONV have been known to circulate in Africa since the mid-1900s, but neither has been genetically characterized by gene and compared in parallel. Furthermore, the susceptibility of peridomestic mosquito species incriminated or suspected in the transmission of ZIKV to SPONV was unknown.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, two geographically distinct strains of SPONV were genetically characterized and compared to nine genetically and geographically distinct ZIKV strains. Additionally, the susceptibility of both SPONV strains was determined in three mosquito species. The open reading frame (ORF) of the SPONV 1952 Nigerian Chuku strain, exhibited a nucleotide and amino acid identity of 97.8% and 99.2%, respectively, when compared to the SPONV 1954 prototype South African SA Ar 94 strain. The ORF of the SPONV Chuku strain exhibited a nucleotide and amino acid identity that ranged from 68.3% to 69.0% and 74.6% to 75.0%, respectively, when compared to nine geographically and genetically distinct strains of ZIKV. The ORF of the nine African and Asian lineage ZIKV strains exhibited limited nucleotide divergence. Aedes aegypti, Ae. albopictus and Culex quinquefasciatus susceptibility and dissemination was low or non-existent following artificial infectious blood feeding of moderate doses of both SPONV strains.

CONCLUSIONS/SIGNIFICANCE

SPONV and ZIKV nucleotide and amino acid divergence coupled with differences in geographic distribution, ecology and vector species support previous reports that these viruses are separate species. Furthermore, the low degree of SPONV infection or dissemination in Ae. albopictus, Ae. aegypti and Cx. quinquefasciatus following exposure to two geographically and genetically distinct virus strains suggest a low potential for these species to serve as vectors.

Zika virus (ZIKV) infection related with immune thrombocytopenic purpura (ITP) exacerbation and antinuclear antibody positivity

A 30-year-old Colombian woman with past history of immune thrombocytopenia (ITP) presented to the emergency room with two days of global headache, arthralgia, myalgia, and low level fever and generalized erythematous rash. Platelets dropped to 9 × 10⁹/L (fourth day of symptoms) without hemorrhagic manifestations but recovered to 30 × 10⁹/L in 24 hours (fifth day). Dengue virus infection, as well as other viral infections, was ruled out. Zika virus (ZIKV) was evaluated in serum and urine samples by real-time reverse-transcriptase polymerase chain reaction (genomic regions within E protein and NS2b protein). Urine sample was positive and serum sample negative for ZIKV, confirming a recent ZIKV infection with urinary tract virus excretion at 7^th day after disease onset. To our knowledge this is the first description of a case of severe immune thrombocytopenia exacerbation and antinuclear antibody positivity induced by ZIKV infection.

Assessment of Local Mosquito Species Incriminates Aedes aegypti as the Potential Vector of Zika Virus in Australia

Background

Within the last 10 years Zika virus (ZIKV) has caused unprecedented epidemics of human disease in the nations and territories of the western Pacific and South America, and continues to escalate in both endemic and non-endemic regions. We evaluated the vector competence of Australian mosquitoes for ZIKV to assess their potential role in virus transmission.

Methodology/Principal Findings

Mosquitoes were exposed to infectious blood meals containing the prototype African ZIKV strain. After 14 days incubation at 28°C and high relative humidity, infection, dissemination and transmission rates were assessed. Infection in Culex annulirostris and Cx. sitiens could not be detected. 8% of Cx. quinquefasciatus were infected, but the virus did not disseminate in this species. Despite having infection rates > 50%, Aedes notoscriptus and Ae. vigilax did not transmit ZIKV. In contrast, Ae. aegypti had infection and transmission rates of 57% and 27%, respectively. In susceptibility trials, the virus dose required to infect 50% (ID₅₀) of Ae. aegypti was10^6.4 tissue culture infectious dose₅₀ (TCID₅₀)/mL. Additionally, a threshold viral load within the mosquito of at least 10^5.1 TCID₅₀ equivalents/mL had to be reached before virus transmission occurred.

Conclusions/Significance

We confirmed Ae. aegypti to be the most likely mosquito vector of ZIKV in Australia, although the restricted distribution of this species will limit the receptive zone to northern Queensland where this species occurs. Importantly, the role in ZIKV transmission of Culex and other Aedes spp. tested will be negligible. Despite being the implicated vector, the relatively high ID₅₀ and need for a high titer disseminated infection in Ae. aegypti suggest that high mosquito population densities will be required to facilitate epidemic ZIKV transmission among the currently immunologically naïve human population in Australia.

Zika virus was first isolated in Uganda in 1947 and exists in a transmission cycle between mosquitoes and non-human primates or humans. Whilst most clinical infections result in a self-limiting febrile illness, Zika virus has recently been linked to neurological syndromes, such as Guillain-Barré syndrome and congenital birth defects. Since 2007, Zika virus has undergone a dramatic range expansion, causing epidemics in nations and territories of the western Pacific and South America. To assess the emergence and transmission risk of Zika virus emerging in Australia, we evaluated the ability of local mosquitoes to become infected with and transmit the prototype African Zika virus strain. In agreement with its substantiated role in Zika virus transmission overseas, Australian Aedes aegypti were shown to be competent vectors. Coupled with its anthropophilic feeding behavior, this species should be considered the primary potential Zika virus vector in Australia. Although other common Australian species, such as Ae. notoscriptus and Ae. vigilax, were readily infected, they did not transmit the virus. The species of Culex tested were either refractory to infection or had a low infection rate. We also demonstrated that the Zika virus dose necessary to infect Ae. aegypti was higher than virus levels reported in infected humans. Finally, a high threshold level of virus circulating through the mosquito body was required before Ae. aegypti transmitted the virus. These results suggest that an outbreak of Zika virus in Australia would require high mosquito population densities and a susceptible human population.

Isolation of Zika Virus Imported from Tonga into Australia

Introduction: The globally emergent Zika virus (ZIKV) is a threat to Australia, given the number of imported cases from epidemic regions and the presence of competent mosquito vectors. We report the isolation of ZIKV from a female traveler who recently returned from Tonga to Brisbane, Queensland, Australia in 2016.

Methods: A specific TaqMan real-time reverse transcriptase polymerase chain reaction assay (RT-PCR) assay was used to detect ZIKV in serum and urine samples. Conventional cell culture techniques and suckling mice were employed in an attempt to isolate ZIKV from serum and urine.

Results: A ZIKV isolate (TS17-2016) was recovered from the serum sample after one passage in suckling mouse brains and harvested 11 days post inoculation. Phylogenetic analysis of complete envelope (E) gene sequences demonstrated TS17-2016 shared 99.9% nucleotide identity with other contemporary sequences from Tonga 2016, Brazil 2015 and French Polynesia 2013 within the Asian lineage.

Discussion: This is the first known report of successful isolation of ZIKV from a human clinical sample in Australia and the first from a traveler from Tonga. This study highlights the potential difficulties in isolating ZIKV from acute clinical samples using conventional cell culture techniques, particularly in non-endemic countries like Australia where access to samples of sufficient viral load is limited. The successful isolation of TS17-2016 will be essential for continued investigations of ZIKV transmission and pathogenicity and will enable the advancement of new preventative control measures extremely relevant to the Australian and Pacific region.

Culex pipiens quinquefasciatus: a potential vector to transmit Zika virus

Zika virus (ZIKV) has become a threat to global health since the outbreak in Brazil in 2015. Although ZIKV is generally considered an Aedes-transmitted pathogen, new evidence has shown that parts of the virus closely resemble Culex-transmitted viruses. Therefore, it is important to evaluate the competence of Culex species for ZIKV to understand their potential as vectors. In this study, female Culex pipiens quinquefasciatus were orally exposed to ZIKV. Mosquito midguts, salivary glands and ovaries were tested for ZIKV to measure infection and dissemination at 2, 4, 6, 8, 12, 16 and 18 days post exposure (pe). In addition, saliva was collected from mosquitoes after infection and infant mice were bitten by infected mosquitoes to measure the transmission ability of Cx. p. quinquefasciatus. The results showed that the peak time of virus appearance in the salivary glands was day 8 pe, with 90% infection rate and an estimated virus titer of 3.92±0.49 lg RNA copies/mL. Eight of the nine infant mice had positive brains after being bitten by infected mosquitoes, which meant that Cx. p. quinquefasciatus could be infected with and transmit ZIKV following oral infection. These laboratory results clearly demonstrate the potential role of Cx. p. quinquefasciatus as a vector of ZIKV in China. Because there are quite different vector management strategies required to control Aedes (Stegomyia) species and Cx. p. quinquefasciatus, an integrated approach may be required should a Zika epidemic occur.

Genome Sequence of a Candidate World Health Organization Reference Strain of Zika Virus for Nucleic Acid Testing

We report here the sequence of a candidate reference strain of Zika virus (ZIKV) developed on behalf of the World Health Organization (WHO). The ZIKV reference strain is intended for use in nucleic acid amplification (NAT)-based assays for the detection and quantification of ZIKV RNA.

Simultaneous detection of Zika, Chikungunya and Dengue viruses by a multiplex real-time RT-PCR assay

BACKGROUND

In the recent past, arboviruses such as Chikungunya (CHIKV) and Zika (ZIKV) have increased their area of endemicity and presented as an emerging global public health threat.

OBJECTIVES

To design an assay for the simultaneous detection of ZIKV, CHIKV and Dengue (DENV) 1-4 from patients with symptoms of arboviral infection. This would be advantageous because of the similar clinical presentation typically encountered with these viruses and their co-circulation in endemic areas.

STUDY DESIGN

In this study we have developed and validated a triplex real time reverse transcription PCR assay using hydrolysis probes targeting the non-structural 5 (NS5) region of ZIKV, non-structural protein 4 (nsP4) from CHIKV and 3' untranslated region (3'UTR) of DENV 1-4.

RESULTS AND CONCLUSIONS

The 95% LOD by the triplex assay was 15 copies/reaction for DENV-1 and less than 10 copies/reaction for all other viruses. The triplex assay was 100% specific and did not amplify any of the other viruses tested. The assay was reproducible and adaptable to testing different specimen types including serum, plasma, urine, placental tissue, brain tissue and amniotic fluid. This assay can be easily implemented for diagnostic testing of patient samples, even in a high throughput laboratory.

A Comprehensive Systems Biology Approach to Studying Zika Virus

Zika virus (ZIKV) is responsible for an ongoing and intensifying epidemic in the Western Hemisphere. We examined the complete predicted proteomes, glycomes, and selectomes of 33 ZIKV strains representing temporally diverse members of the African lineage, the Asian lineage, and the current outbreak in the Americas. Derivation of the complete selectome is an 'omics' approach to identify distinct evolutionary pressures acting on different features of an organism. Employment of the M8 model did not show evidence of global diversifying selection acting on the ZIKV polyprotein; however, a mixed effect model of evolution showed strong evidence (P<0.05) for episodic diversifying selection acting on specific sites. Single nucleotide polymorphisms (SNPs) were predictably frequent across strains relative to the derived consensus sequence. None of the 9 published detection procedures utilize targets that share 100% identity across the 33 strains examined, indicating that ZIKV escape from molecular detection is predictable. The predicted O-linked glycome showed marked diversity across strains; however, the N-linked glycome was highly stable. All Asian and American strains examined were predicted to include glycosylation of E protein ASN154, a modification proposed to mediate neurotropism, whereas the modification was not predicted for African strains. SNP diversity, episodic diversifying selection, and differential glycosylation, particularly of ASN154, may have major biological implications for ZIKV disease. Taken together, the systems biology perspective of ZIKV indicates: a.) The recently emergent Asian/American N-glycotype is mediating the new and emerging neuropathogenic potential of ZIKV; and b.) further divergence at specific sites is predictable as endemnicity is established in the Americas.

Culex quinquefasciatus from Rio de Janeiro Is Not Competent to Transmit the Local Zika Virus

BACKGROUND

The Americas have suffered a dramatic epidemic of Zika since May in 2015, when Zika virus (ZIKV) was first detected in Brazil. Mosquitoes belonging to subgenus Stegomyia of Aedes, particularly Aedes aegypti, are considered the primary vectors of ZIKV. However, the rapid spread of the virus across the continent raised several concerns about the transmission dynamics, especially about potential mosquito vectors. The purpose of this work was to assess the vector competence of the house mosquito Culex quinquefasciatus from an epidemic Zika area, Rio de Janeiro, Brazil, for local circulating ZIKV isolates.

METHODOLOGY/PRINCIPAL FINDINGS

Culex quinquefasciatus and Ae. aegypti (positive control of ZIKV infection) from Rio de Janeiro were orally exposed to two ZIKV strains isolated from human cases from Rio de Janeiro (Rio-U1 and Rio-S1). Fully engorged mosquitoes were held in incubators at 26 ± 1°C, 12 h:12 h light:dark cycle and 70 ± 10% humidity. For each combination mosquito population-ZIKV strain, 30 specimens were examined for infection, dissemination and transmission rates, at 7, 14 and 21 days after virus exposure by analyzing body (thorax plus abdomen), head and saliva respectively. Infection rates were minimal to completely absent in all Cx. quinquefasciatus-virus combinations and were significantly high for Ae. aegypti. Moreover, dissemination and transmission were not detected in any Cx. quinquefasciatus mosquitoes whatever the incubation period and the ZIKV isolate. In contrast, Ae. aegypti ensured high viral dissemination and moderate to very high transmission.

CONCLUSIONS/SIGNIFICANCE

The southern house mosquito Cx. quinquefasciatus from Rio de Janeiro was not competent to transmit local strains of ZIKV. Thus, there is no experimental evidence that Cx. quinquefasciatus likely plays a role in the ZIKV transmission. Consequently, at least in Rio, mosquito control to reduce ZIKV transmission should remain focused on Ae. aegypti.

Contribution of intertwined loop to membrane association revealed by Zika virus full-length NS1 structure

The association of Zika virus (ZIKV) infections with microcephaly and neurological diseases has highlighted an emerging public health concern. Here, we report the crystal structure of the full‐length ZIKV nonstructural protein 1 (NS1), a major host‐interaction molecule that functions in flaviviral replication, pathogenesis, and immune evasion. Of note, a long intertwined loop is observed in the wing domain of ZIKV NS1, and forms a hydrophobic “spike”, which can contribute to cellular membrane association. For different flaviviruses, the amino acid sequences of the “spike” are variable but their common characteristic is either hydrophobic or positively charged, which is a beneficial feature for membrane binding. Comparative studies with West Nile and Dengue virus NS1 structures reveal conserved features, but diversified electrostatic characteristics on both inner and outer faces. Our results suggest different mechanisms of flavivirus pathogenesis and should be considered during the development of diagnostic tools.

Vertical Transmission of Zika Virus in Aedes aegypti Mosquitoes

Previous experimental studies have demonstrated that a number of mosquito-borne flavivirus pathogens are vertically transmitted in their insect vectors, providing a mechanism for these arboviruses to persist during adverse climatic conditions or in the absence of a susceptible vertebrate host. In this study, designed to test whether Zika virus (ZIKV) could be vertically transmitted, female Aedes aegypti and Aedes albopictus were injected with ZIKV, and their F₁ adult progeny were tested for ZIKV infection. Six of 69 Ae. aegypti pools, comprised of a total of 1,738 F₁ adults, yielded ZIKV upon culture, giving a minimum filial infection rate of 1:290. In contrast, none of 803 F₁Ae. albopictus adults (32 pools) yielded ZIKV. The MFIR for Ae. aegypti was comparable to MFIRs reported for other flaviviruses in mosquitoes, including dengue, Japanese encephalitis, yellow fever, West Nile, and St. Louis encephalitis viruses. The results suggest that vertical transmission may provide a potential mechanism for the virus to survive during adverse conditions.

Imaging of congenital Zika virus infection: the route to identification of prognostic factors

Zika virus (ZIKV) has recently emerged as a novel teratogenic agent associated with severe neurological complications. The risk associated with maternal infection remains to be exactly defined but appears to be significant. Like other TORCH agents (toxoplasmosis, other agents, rubella, cytomegalovirus and herpes simplex), it is unlikely that all affected fetuses will be symptomatic at birth. It is therefore urgent to better define the spectrum of anomalies observed in infected fetuses to provide adequate parental counseling. In this review, we provide a comprehensive analysis of major cases described to date and highlight specific prenatal and postnatal radiological findings of congenital ZIKV infection. A total of 19 reports were included in our analysis. ZIKV seemed to harbor a specific tropism for the central nervous system, and anomalies were mostly limited to the brain. Major radiological findings were ventriculomegaly, diffuse calcifications and signs of abnormal gyration as well as cortical development. In addition, a significant number of fetuses suffered from intra uterine growth restriction. Based on these findings, we provide recommendations for adequate radiological monitoring of at-risk pregnancies. © 2016 John Wiley & Sons, Ltd.

Evidence of the presence of the Zika virus in Mexico since early 2015

To assess the possible circulation of Zika virus (ZIKV) prior to the first documented case in Mexico, we reanalyzed the stored samples from the states of Veracruz and Yucatán, which were originally collected to test for dengue (DENV) and chikungunya (CHIKV) but were negative for these viruses despite the symptomatology. The samples were originally collected between the 30 and 46 epidemiological weeks (EW) when the ZIKV was not yet declared as a Public Health Emergency of International Concern (PHEIC). From the total 4016 negative samples, a total of one hundred samples, 50 from Veracruz (CHIK^- DENV^-) and 50 from Yucatán (4 CHIK^- DENV^- and 46 CHIK^- or DENV^-), were tested for Zika virus by using RT-PCR. Results showed that in Veracruz and Yucatán, 20 % (10/50) and 70 % (35/50) were, respectively, ZIKV positive, indicating unequivocally the presence of ZIKV at least since July 2015. We also tested non-confirmed suspect measles cases from early 2015 for ZIKV by RT-PCR. Remarkably in 11 Mexican states, 86 % (18/21) were positive with the earlier symptoms onset as early as May 2015. Finally, RT-PCR analyses on RNA extracted from Aedes aegypti mosquitoes captured from January to March 2015 showed the presence of ZIKV, strongly suggesting that the vector was already carrying the virus at the start of 2015.

Zika virus: from pathogenesis to disease control

Zika virus is a mosquito-borne flavivirus discovered in Uganda in 1947. The virus has emerged in recent years and spread in the Pacific Area and the Americas, where it has caused large human outbreaks. The factors involved in the virus's emergence are still unknown, but probably include its introduction in naïve environments characterised by the presence of high densities of competent Aedes spp. mosquitoes and susceptible human hosts in urban areas. Unique features of Zika virus infection are sexual and transplacental transmission and associated neurological morbidities, i.e. Guillain-Barré syndrome and fetal microcephaly. Diagnosis relies on the detection of viral nucleic acids in biological samples, while detection of a specific antibody response may be inconclusive because of the broad cross-reactivity of antibodies among flaviviruses. Experimental studies have clarified some mechanisms of Zika virus pathogenesis and have identified potential targets for antiviral drugs. In animal models, the virus can infect and efficiently replicate in the placenta and in the brain, and induce fetal demise or neural damage, recapitulating human diseases. These animal models have been used to evaluate candidate vaccines and promising results have been obtained.

Complete Genome Sequences of Three Historically Important, Spatiotemporally Distinct, and Genetically Divergent Strains of Zika Virus: MR-766, P6-740, and PRVABC-59

Here, we report the 10,807-nucleotide-long consensus RNA genome sequences of three spatiotemporally distinct and genetically divergent Zika virus strains, with the functionality of their genomic sequences substantiated by reverse genetics: MR-766 (African lineage, Uganda, 1947), P6-740 (Asian lineage, Malaysia, 1966), and PRVABC-59 (Asian lineage-derived American strain, Puerto Rico, 2015).

Assessing the global threat from Zika virus

First discovered in 1947, Zika virus (ZIKV) infection remained a little-known tropical disease until 2015, when its apparent association with a considerable increase in the incidence of microcephaly in Brazil raised alarms worldwide. There is limited information on the key factors that determine the extent of the global threat from ZIKV infection and resulting complications. Here, we review what is known about the epidemiology, natural history, and public health effects of ZIKV infection, the empirical basis for this knowledge, and the critical knowledge gaps that need to be filled.

Potent Allosteric Dengue Virus NS5 Polymerase Inhibitors: Mechanism of Action and Resistance Profiling

Flaviviruses comprise major emerging pathogens such as dengue virus (DENV) or Zika virus (ZIKV). The flavivirus RNA genome is replicated by the RNA-dependent-RNA polymerase (RdRp) domain of non-structural protein 5 (NS5). This essential enzymatic activity renders the RdRp attractive for antiviral therapy. NS5 synthesizes viral RNA via a “de novo” initiation mechanism. Crystal structures of the flavivirus RdRp revealed a “closed” conformation reminiscent of a pre-initiation state, with a well ordered priming loop that extrudes from the thumb subdomain into the dsRNA exit tunnel, close to the “GDD” active site. To-date, no allosteric pockets have been identified for the RdRp, and compound screening campaigns did not yield suitable drug candidates. Using fragment-based screening via X-ray crystallography, we found a fragment that bound to a pocket of the apo-DENV RdRp close to its active site (termed “N pocket”). Structure-guided improvements yielded DENV pan-serotype inhibitors of the RdRp de novo initiation activity with nano-molar potency that also impeded elongation activity at micro-molar concentrations. Inhibitors exhibited mixed inhibition kinetics with respect to competition with the RNA or GTP substrate. The best compounds have EC₅₀ values of 1–2 μM against all four DENV serotypes in cell culture assays. Genome-sequencing of compound-resistant DENV replicons, identified amino acid changes that mapped to the N pocket. Since inhibitors bind at the thumb/palm interface of the RdRp, this class of compounds is proposed to hinder RdRp conformational changes during its transition from initiation to elongation. This is the first report of a class of pan-serotype and cell-active DENV RdRp inhibitors. Given the evolutionary conservation of residues lining the N pocket, these molecules offer insights to treat other serious conditions caused by flaviviruses.

Dengue virus (DENV) is the world’s most prevalent mosquito-borne viral disease and nearly 40% of the world’s population is at risk of infection. Currently, no specific drugs are available to treat dengue or other flaviviral diseases. DENV NS5 is a large protein of 900 amino acids composed of two domains with key enzymatic activities for viral RNA replication in the host cell and constitutes a prime target for the design of anti-viral inhibitors. We performed a fragment-based screening by X-ray crystallography targeting the DENV NS5 polymerase and identified an allosteric binding pocket at the base of the thumb subdomain close to the enzyme active site. Potent inhibitors active in both DENV polymerase biochemical and cell-based assays were developed through structure-guided design. Resistant virus replicons grown in the presence of the inhibitor, harbored amino acid changes that mapped to the compound binding site. The proposed mode of action for this class of inhibitors is by impeding RdRp protein conformational changes during the transition from initiation to elongation phase of enzyme activity.

Zika, dengue, and chikungunya co-infection in a pregnant woman from Colombia

The clinical findings of a pregnant woman from Colombia with a triple co-infection caused by dengue, chikungunya, and Zika viruses are described. Weekly obstetric ultrasounds from 14.6 to 29 weeks of gestation were normal. She remains under follow-up and management according to the standard guidelines for the management of Zika virus-infected pregnant women.

The global threat of Zika virus to pregnancy: epidemiology, clinical perspectives, mechanisms, and impact

Zika virus (ZIKV) is a mosquito-borne flavivirus that has newly emerged as a significant global threat, especially to pregnancy. Recent major outbreaks in the Pacific and in Central and South America have been associated with an increased incidence of microcephaly and other abnormalities of the central nervous system in neonates. The causal link between ZIKV infection during pregnancy and microcephaly is now strongly supported. Over 2 billion people live in regions conducive to ZIKV transmission, with ~4 million infections in the Americas predicted for 2016. Given the scale of the current pandemic and the serious and long-term consequences of infection during pregnancy, the impact of ZIKV on health services and affected communities could be enormous. This further highlights the need for a rapid global public health and research response to ZIKV to limit and prevent its impact through the development of therapeutics, vaccines, and improved diagnostics. Here we review the epidemiology of ZIKV; the threat to pregnancy; the clinical consequences and broader impact of ZIKV infections; and the virus biology underpinning new interventions, diagnostics, and insights into the mechanisms of disease.

Zika virus: An update on epidemiology, pathology, molecular biology, and animal model

Zika virus (ZIKV) was first described in 1947, and became a health emergency problem in 2016 when its association with fetal microcephaly cases was confirmed by Centers for Disease Control and Prevention (CDC) in the United States. To date, ZIKV infection has been documented in 66 countries. ZIKV is recognized as a neurotropic virus and numerous diseases manifested in multiple neurological disorders have been described, mainly in countries that have been exposed to ZIKV after the 2007 outbreak in the Federated States of Micronesia. The most dramatic consequence of ZIKV infection documented is the abrupt increase in fetal microcephaly cases in Brazil. Here, we present an update of the published research progress in the past few months. J. Med. Virol. 88:1291-1296, 2016. © 2016 Wiley Periodicals, Inc.

Epidemiology of Zika virus, 1947-2007

INTRODUCTION

Since 1947, Zika virus has been identified sporadically in humans in Africa and Asia; however, clinically consequential Zika virus disease had not been documented prior to the current outbreak in the Americas. Considering 6 decades have passed since the first identification of the virus, it is perhaps unexpected that Zika virus was recognised only recently as capable of causing disease epidemics. Substantial work on understanding the epidemiology of Zika virus has been conducted since the virus' first outbreak in 2007 in Micronesia; however, there has been little study of the earlier data on Zika virus.

METHODS

A systematic literature search was conducted to identify evidence of Zika virus infection in humans from 1947 to 2007. Data extracted included seroprevalence of Zika virus infection, age distributions of positive test results and serologic test modalities used. Country-level and age-specific seroprevalence was calculated. Estimates of seroprevalence by different serologic test modalities were compared.

RESULTS

12 026 citations were retrieved by the literature search, and 76 articles were included in this review. Evidence of Zika virus infection in humans was found in 29 countries in Africa, 8 countries in Asia and 1 country in Europe. Country-level seroprevalence of Zika virus infection ranged from 0.4% to 53.3%. Seroprevalence of Zika virus infection was found to increase across the lifespan; 15-40% of reproductive-age individuals may have been previously infected. No significant difference was found between estimates of seroprevalence by different serologic test modalities.

DISCUSSION

Zika virus has likely been endemic for decades in certain regions of the world; however, the majority of reproductive-age individuals have likely not been infected. Historical evidence of Zika virus infection exists regardless of the serologic test modality used.

A robust method for the rapid generation of recombinant Zika virus expressing the GFP reporter gene

Zika virus (ZIKV) infection is a major public health problem with severe human congenital and neurological anomalies. The screening of anti-ZIKV compounds and neutralizing antibodies needs reliable and rapid virus-based assays. Here, we described a convenient method leading to the rapid production of molecular clones of ZIKV. To generate a molecular clone of ZIKV strain MR766(NIID), the viral genome was directly assembled into Vero cells after introduction of four overlapping synthetic fragments that cover the full-length genomic RNA sequence. Such strategy has allowed the production of a recombinant ZIKV expressing the GFP reporter gene that is stable over two culturing rounds on Vero cells. Our data demonstrate that the ZIKV reporter virus is a very reliable GFP-based tool for analyzing viral growth and measuring the neutralizing antibody as well as rapid screening of antiviral effect of different classes of inhibitors.

Projected Zika Virus Importation and Subsequent Ongoing Transmission after Travel to the 2016 Olympic and Paralympic Games - Country-Specific Assessment, July 2016

Zika virus belongs to the genus Flavivirus of the family Flaviviridae; it is transmitted to humans primarily through the bite of an infected Aedes species mosquito (e.g., Ae. aegypti and Ae. albopictus) (1). Zika virus has been identified as a cause of congenital microcephaly and other serious brain defects (2). As of June 30, 2016, CDC had issued travel notices for 49 countries and U.S. territories across much of the Western hemisphere (3), including Brazil, where the 2016 Olympic and Paralympic Games (Games of the XXXI Olympiad, also known as Rio 2016; Games) will be hosted in Rio de Janeiro in August and September 2016. During the Games, mosquito-borne Zika virus transmission is expected to be low because August and September are winter months in Brazil, when cooler and drier weather typically reduces mosquito populations (4). CDC conducted a risk assessment to predict those countries susceptible to ongoing Zika virus transmission resulting from introduction by a single traveler to the Games. Whereas all countries are at risk for travel-associated importation of Zika virus, CDC estimated that 19 countries currently not reporting Zika outbreaks have the environmental conditions and population susceptibility to sustain mosquito-borne transmission of Zika virus if a case were imported from infection at the Games. For 15 of these 19 countries, travel to Rio de Janeiro during the Games is not estimated to increase substantially the level of risk above that incurred by the usual aviation travel baseline for these countries. The remaining four countries, Chad, Djibouti, Eritrea, and Yemen, are unique in that they do not have a substantial number of travelers to any country with local Zika virus transmission, except for anticipated travel to the Games. These four countries will be represented by a projected, combined total of 19 athletes (plus a projected delegation of about 60 persons), a tiny fraction of the 350,000-500,000 visitors expected at the Games.* Overall travel volume to the Games represents a very small fraction (<0.25%) of the total estimated 2015 travel volume to Zika-affected countries,(†) highlighting the unlikely scenario that Zika importation would be solely attributable to travel to the Games. To prevent Zika virus infection and its complications among athletes and visitors to the Games and importation of Zika virus into countries that could sustain local transmission, pregnant women should not travel to the Games, mosquito bites should be avoided while traveling and for 3 weeks after returning home, and measures should be taken to prevent sexual transmission (Box).

Outbreak of Zika Virus Infection, Chiapas State, Mexico, 2015, and First Confirmed Transmission by Aedes aegypti Mosquitoes in the Americas

BACKGROUND

 After decades of obscurity, Zika virus (ZIKV) has spread through the Americas since 2015 accompanied by congenital microcephaly and Guillain-Barré syndrome. Although these epidemics presumably involve transmission by Aedes aegypti, no direct evidence of vector involvement has been reported, prompting speculation that other mosquitoes such as Culex quinquefasciatus could be involved.

METHODS

 We detected an outbreak of ZIKV infection in southern Mexico in late 2015. Sera from suspected ZIKV-infected patients were analyzed for viral RNA and antibodies. Mosquitoes were collected in and around patient homes and tested for ZIKV.

RESULTS

 Of 119 suspected ZIKV-infected patients, 25 (21%) were confirmed by RT-PCR of serum collected 1-8 days after the onset of signs and symptoms including rash, arthralgia, headache, pruritus, myalgia, and fever. Of 796 mosquitoes collected, A. aegypti yielded ZIKV detection by RT-PCR in 15 of 55 pools (27.3%). No ZIKV was detected in C. quinquefasciatus ZIKV sequences derived from sera and mosquitoes showed a monophyletic relationship suggestive of a point source introduction from Guatemala.

CONCLUSIONS

 These results demonstrate the continued, rapid northward progression of ZIKV into North America with typically mild disease manifestations, and implicate A. aegypti for the first time as a principal vector in North America.

Zika virus as a causative agent for primary microencephaly: the evidence so far

Zika virus (ZIKV) infection has been associated with congenital microcephaly and peripheral neuropathy. The ongoing epidemic has triggered swift responses in the scientific community, and a number of recent reports have now confirmed a causal relationship between ZIKV infection and birth defect. In particular, ZIKV has been shown to be capable of compromising and crossing the placental barrier and infect the developing fetal brain, resulting in the demise and functional impairment of neuroprogenitor cells critical for fetal cortex development. Here, the evidence for ZIKV as a teratogenic agent that causes microcephaly is reviewed, and its association with other disorders is discussed.

Emerging Role of Zika Virus in Adverse Fetal and Neonatal Outcomes

The rapid spread of the Zika virus (ZIKV) in the Americas and its potential association with thousands of suspected cases of microcephaly in Brazil and higher rates of Guillain-Barré syndrome meet the conditions for a Public Health Emergency of International Concern, as stated by the World Health Organization in February 2016. Two months later, the Centers for Disease Control and Prevention (CDC) announced that the current available evidence supports the existence of a causal relationship between prenatal Zika virus infection and microcephaly and other serious brain anomalies. Microcephaly can be caused by several factors, and its clinical course and prognosis are difficult to predict. Other pathogens with proven teratogenicity have been identified long before the current ZIKV epidemic. Despite the growing number of cases with maternal signs of infection and/or presence of ZIKV in tissues of affected newborns or fetuses, it is currently difficult to assess the magnitude of increase of microcephaly prevalence in Brazil, as well as the role of other factors in the development of congenital neurological conditions. Meanwhile, health agencies and medical organizations have issued cautious guidelines advising health care practitioners and expectant couples traveling to, returning from, or living in affected areas. Analogous to dengue virus (DENV) epidemics, ZIKV has the potential to become endemic in all countries infested by Aedes mosquitoes, while new mutations could impact viral replication in humans, leading to increased virulence and consequently heightened chances of viral transmission to additional naive mosquito vectors. Studies are urgently needed to answer the questions surrounding ZIKV and its role in congenital neurological conditions.

Approved Antiviral Drugs over the Past 50 Years

Since the first antiviral drug, idoxuridine, was approved in 1963, 90 antiviral drugs categorized into 13 functional groups have been formally approved for the treatment of the following 9 human infectious diseases: (i) HIV infections (protease inhibitors, integrase inhibitors, entry inhibitors, nucleoside reverse transcriptase inhibitors, nonnucleoside reverse transcriptase inhibitors, and acyclic nucleoside phosphonate analogues), (ii) hepatitis B virus (HBV) infections (lamivudine, interferons, nucleoside analogues, and acyclic nucleoside phosphonate analogues), (iii) hepatitis C virus (HCV) infections (ribavirin, interferons, NS3/4A protease inhibitors, NS5A inhibitors, and NS5B polymerase inhibitors), (iv) herpesvirus infections (5-substituted 2'-deoxyuridine analogues, entry inhibitors, nucleoside analogues, pyrophosphate analogues, and acyclic guanosine analogues), (v) influenza virus infections (ribavirin, matrix 2 protein inhibitors, RNA polymerase inhibitors, and neuraminidase inhibitors), (vi) human cytomegalovirus infections (acyclic guanosine analogues, acyclic nucleoside phosphonate analogues, pyrophosphate analogues, and oligonucleotides), (vii) varicella-zoster virus infections (acyclic guanosine analogues, nucleoside analogues, 5-substituted 2'-deoxyuridine analogues, and antibodies), (viii) respiratory syncytial virus infections (ribavirin and antibodies), and (ix) external anogenital warts caused by human papillomavirus infections (imiquimod, sinecatechins, and podofilox). Here, we present for the first time a comprehensive overview of antiviral drugs approved over the past 50 years, shedding light on the development of effective antiviral treatments against current and emerging infectious diseases worldwide.

A rhesus macaque model of Asian-lineage Zika virus infection

Infection with Asian-lineage Zika virus (ZIKV) has been associated with Guillain-Barré syndrome and fetal abnormalities, but the underlying mechanisms remain poorly understood. Animal models of infection are thus urgently needed. Here we show that rhesus macaques are susceptible to infection by an Asian-lineage ZIKV closely related to strains currently circulating in the Americas. Following subcutaneous inoculation, ZIKV RNA is detected in plasma 1 day post infection (d.p.i.) in all animals (N=8, including 2 pregnant animals), and is also present in saliva, urine and cerebrospinal fluid. Non-pregnant and pregnant animals remain viremic for 21 days and for up to at least 57 days, respectively. Neutralizing antibodies are detected by 21 d.p.i. Rechallenge 10 weeks after the initial challenge results in no detectable virus replication, indicating protective immunity against homologous strains. Therefore, Asian-lineage ZIKV infection of rhesus macaques provides a relevant animal model for studying pathogenesis and evaluating potential interventions against human infection, including during pregnancy.

Human antibody responses after dengue virus infection are highly cross-reactive to Zika virus

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus of significant public health concern. ZIKV shares a high degree of sequence and structural homology compared with other flaviviruses, including dengue virus (DENV), resulting in immunological cross-reactivity. Improving our current understanding of the extent and characteristics of this immunological cross-reactivity is important, as ZIKV is presently circulating in areas that are highly endemic for dengue. To assess the magnitude and functional quality of cross-reactive immune responses between these closely related viruses, we tested acute and convalescent sera from nine Thai patients with PCR-confirmed DENV infection against ZIKV. All of the sera tested were cross-reactive with ZIKV, both in binding and in neutralization. To deconstruct the observed serum cross-reactivity in depth, we also characterized a panel of DENV-specific plasmablast-derived monoclonal antibodies (mAbs) for activity against ZIKV. Nearly half of the 47 DENV-reactive mAbs studied bound to both whole ZIKV virion and ZIKV lysate, of which a subset also neutralized ZIKV. In addition, both sera and mAbs from the dengue-infected patients enhanced ZIKV infection of Fc gamma receptor (FcγR)-bearing cells in vitro. Taken together, these findings suggest that preexisting immunity to DENV may impact protective immune responses against ZIKV. In addition, the extensive cross-reactivity may have implications for ZIKV virulence and disease severity in DENV-experienced populations.

Dengue virus sero-cross-reactivity drives antibody-dependent enhancement of infection with zika virus

Zika virus (ZIKV) was discovered in 1947 and was thought to lead to relatively mild disease. The recent explosive outbreak of ZIKV in South America has led to widespread concern with reports of neurological sequelae ranging from Guillain Barré syndrome to microcephaly. ZIKV infection has occurred in areas previously exposed to dengue, a flavivirus closely related to ZIKV. Here we investigate the serological crossreaction between the two viruses. Dengue immune plasma substantially crossreacted with ZIKV and could drive antibody-dependent enhancement of ZIKV infection. Using a panel of human anti-dengue monoclonal antibodies we showed that most antibodies reacting to dengue envelope protein also reacted to ZIKV. Antibodies to linear epitopes including the immunodominant fusion loop epitope while able to bind ZIKV could not neutralize the virus but instead promoted ADE. These data indicate that dengue immunity may drive higher ZIKV replication and have clear implications for disease pathogenesis and future ZIKV and dengue vaccine programs.

Identification of Zika Virus and Dengue Virus Dependency Factors using Functional Genomics

The flaviviruses dengue virus (DENV) and Zika virus (ZIKV) are severe health threats with rapidly expanding ranges. To identify the host cell dependencies of DENV and ZIKV, we completed orthologous functional genomic screens using RNAi and CRISPR/Cas9 approaches. The screens recovered the ZIKV entry factor AXL as well as multiple host factors involved in endocytosis (RAB5C and RABGEF), heparin sulfation (NDST1 and EXT1), and transmembrane protein processing and maturation, including the endoplasmic reticulum membrane complex (EMC). We find that both flaviviruses require the EMC for their early stages of infection. Together, these studies generate a high-confidence, systems-wide view of human-flavivirus interactions and provide insights into the role of the EMC in flavivirus replication.

Nucleotide composition of the Zika virus RNA genome and its codon usage

BACKGROUND

RNA viruses have genomes with a distinct nucleotide composition and codon usage. We present the global characteristics of the RNA genome of Zika virus (ZIKV), an emerging pathogen within the Flavivirus genus. ZIKV was first isolated in 1947 in Uganda, caused a widespread epidemic in South and Central America and the Caribbean in 2015 and has recently been associated with microcephaly in newborns.

METHODS

The nearly 11 kb positive-stranded RNA genome of ZIKV was analyzed for its nucleotide composition, also in the context of the folded RNA molecule. Nucleotide trends were investigated along the genome length by skew analyses and we analyzed the codons used for translation of the ZIKV proteins.

RESULTS

ZIKV RNA has a biased nucleotide composition in being purine-rich and pyrimidine-poor. This preference for purines is a general characteristic of the mosquito-borne and tick-borne flaviviruses. The virus-specific nucleotide bias is further enriched in the unpaired, single-stranded regions of the structured ZIKV RNA genome, thus further imposing this ZIKV-specific signature. The codons used for translation of the ZIKV proteins is also unusual, but we show that it is the underlying bias in nucleotide composition of the viral RNA that largely dictates these codon preferences.

CONCLUSIONS

The ZIKV RNA genome has a biased nucleotide composition that dictates the codon usage of this flavivirus. We discuss the evolutionary scenarios and molecular mechanisms that may be responsible for these distinctive ZIKV RNA genome features.

The IFITMs Inhibit Zika Virus Replication

Zika virus has emerged as a severe health threat with a rapidly expanding range. The IFITM family of restriction factors inhibits the replication of a broad range of viruses, including the closely related flaviruses West Nile virus and dengue virus. Here, we show that IFITM1 and IFITM3 inhibit Zika virus infection early in the viral life cycle. Moreover, IFITM3 can prevent Zika-virus-induced cell death. These results suggest that strategies to boost the actions and/or levels of the IFITMs might be useful for inhibiting a broad range of emerging viruses.