Spondweni virus infection in a foreign resident of Upper Volta

Primary infection with Zika virus provides one-way heterologous protection against Spondweni virus infection in rhesus macaques

Spondweni virus (SPONV) is the closest known relative of Zika virus (ZIKV). SPONV pathogenesis resembles that of ZIKV in pregnant mice, and both viruses are transmitted by Aedes aegypti mosquitoes. We aimed to develop a translational model to further understand SPONV transmission and pathogenesis. We found that cynomolgus macaques (Macaca fascicularis) inoculated with ZIKV or SPONV were susceptible to ZIKV but resistant to SPONV infection. In contrast, rhesus macaques (Macaca mulatta) supported productive infection with both ZIKV and SPONV and developed robust neutralizing antibody responses. Crossover serial challenge in rhesus macaques revealed that SPONV immunity did not protect against ZIKV infection, whereas ZIKV immunity was fully protective against SPONV infection. These findings establish a viable model for future investigation into SPONV pathogenesis and suggest that the risk of SPONV emergence is low in areas with high ZIKV seroprevalence due to one-way cross-protection between ZIKV and SPONV.

Quantitative real time PCR detection of Saboya virus: A flavivirus member of yellow fever genetic group

The genus Flavivirus in the Flaviridae contains arthropod born viruses associated with high public health burdens like Zika, Dengue or Yellow fever. Saboya virus (SABV) is an understudied flavivirus grouping in the same genetic sub-group as Yellow Fever Virus (YFV) together with Sepik virus (SEPV) and Wesselbron virus (WSLV). Flavivirus infections are characterized by non-specific clinical presentations resulting in a high risk of misdiagnosis. SABV virus has been shown to circulate in the Sahelian zone and in central Africa. To study this virus we a qRT-PCR system based on TaqMan chemistry was developed to allow rapid and specific detection of SABV. The SABV assay was evaluated on available SABV isolates and others flaviviruses (DENV, ZIKV, YFV, WNV, KEDV). The system reliably detected all used SABV strains without cross amplification of other flaviviruses. In term of sensitivity the SABV assay detect up to 40.25 copies of SABV standard DNA molecule per ul. This system can be easily added to the available panel of arboviruses detection assays as a reliable tool to study virus prevalence in human, vertebrate and insect-vector samples.

The RNA Secondary Structure Analysis Reveals Potential for Emergence of Pathogenic Flaviviruses

The Flavivirus genus is divided into four groups: Mosquito-borne flaviviruses, Tick-borne flaviviruses, no-known vector flaviviruses, and Insect specific flaviviruses. Millions of people are affected worldwide every year due to the flaviviral infections. The 5' UTR of the RNA genome plays a critical role in the biology of flaviviruses. To explore any correlation between the topology of the 5' UTR and pathogenesis, a global scale study of the RNA secondary structure of different groups of flaviviruses has been conducted. We found that most of the pathogenic flaviviruses, irrespective of their mode of transmission, tend to form a Y shaped topology in the Stem loop A of the 5' UTR. Some of the current non-pathogenic flaviviruses were also observed to form Y shaped structure. Based on this study, it has been proposed that the flaviviruses having the Y shaped topology in their 5' UTR regions may have the potential to become pathogenic.

Animal board invited review: Risks of zoonotic disease emergence at the interface of wildlife and livestock systems

The ongoing coronavirus disease 19s pandemic has yet again demonstrated the importance of the human-animal interface in the emergence of zoonotic diseases, and in particular the role of wildlife and livestock species as potential hosts and virus reservoirs. As most diseases emerge out of the human-animal interface, a better understanding of the specific drivers and mechanisms involved is crucial to prepare for future disease outbreaks. Interactions between wildlife and livestock systems contribute to the emergence of zoonotic diseases, especially in the face of globalization, habitat fragmentation and destruction and climate change. As several groups of viruses and bacteria are more likely to emerge, we focus on pathogenic viruses of the Bunyavirales, Coronaviridae, Flaviviridae, Orthomyxoviridae, and Paramyxoviridae, as well as bacterial species including Mycobacterium sp., Brucella sp., Bacillus anthracis and Coxiella burnetii. Noteworthy, it was difficult to predict the drivers of disease emergence in the past, even for well-known pathogens. Thus, an improved surveillance in hotspot areas and the availability of fast, effective, and adaptable control measures would definitely contribute to preparedness. We here propose strategies to mitigate the risk of emergence and/or re-emergence of prioritized pathogens to prevent future epidemics.

Mosquito-Associated Viruses and Their Related Mosquitoes in West Africa

Mosquito-associated viruses (MAVs), including mosquito-specific viruses (MSVs) and mosquito-borne (arbo)viruses (MBVs), are an increasing public, veterinary, and global health concern, and West Africa is projected to be the next front for arboviral diseases. As in-depth knowledge of the ecologies of both western African MAVs and related mosquitoes is still limited, we review available and comprehensive data on their diversity, abundance, and distribution. Data on MAVs’ occurrence and related mosquitoes were extracted from peer-reviewed publications. Data on MSVs, and mosquito and vertebrate host ranges are sparse. However, more data are available on MBVs (i.e., dengue, yellow fever, chikungunya, Zika, and Rift Valley fever viruses), detected in wild and domestic animals, and humans, with infections more concentrated in urban areas and areas affected by strong anthropogenic changes. Aedes aegypti, Culex quinquefasciatus, and Aedes albopictus are incriminated as key arbovirus vectors. These findings outline MAV, related mosquitoes, key knowledge gaps, and future research areas. Additionally, these data highlight the need to increase our understanding of MAVs and their impact on host mosquito ecology, to improve our knowledge of arbovirus transmission, and to develop specific strategies and capacities for arboviral disease surveillance, diagnostic, prevention, control, and outbreak responses in West Africa.

Flavivirus maturation leads to the formation of an occupied lipid pocket in the surface glycoproteins

Flaviviruses such as Dengue (DENV) or Zika virus (ZIKV) assemble into an immature form within the endoplasmatic reticulum (ER), and are then processed by furin protease in the trans-Golgi. To better grasp maturation, we carry out cryo-EM reconstructions of immature Spondweni virus (SPOV), a human flavivirus of the same serogroup as ZIKV. By employing asymmetric localised reconstruction we push the resolution to 3.8 Å, enabling us to refine an atomic model which includes the crucial furin protease recognition site and a conserved Histidine pH-sensor. For direct comparison, we also solve structures of the mature forms of SPONV and DENV to 2.6 Å and 3.1 Å, respectively. We identify an ordered lipid that is present in only the mature forms of ZIKV, SPOV, and DENV and can bind as a consequence of rearranging amphipathic stem-helices of E during maturation. We propose a structural role for the pocket and suggest it stabilizes mature E.

Spondweni virus causes fetal harm in Ifnar1-/- mice and is transmitted by Aedes aegypti mosquitoes

Spondweni virus (SPONV) is the most closely related known flavivirus to Zika virus (ZIKV). Its pathogenic potential and vector specificity have not been well defined. SPONV has been found predominantly in Africa, but was recently detected in a pool of Culex quinquefasciatus mosquitoes in Haiti. Here we show that SPONV can cause significant fetal harm, including demise, comparable to ZIKV, in a mouse model of vertical transmission. Following maternal inoculation, we detected infectious SPONV in placentas and fetuses, along with significant fetal and placental histopathology, together suggesting vertical transmission. To test vector competence, we exposed Aedes aegypti and Culex quinquefasciatus mosquitoes to SPONV-infected bloodmeals. Aedes aegypti could efficiently transmit SPONV, whereas Culex quinquefasciatus could not. Our results suggest that SPONV has the same features that made ZIKV a public health risk.

Spondweni Virus in Field-Caught Culex quinquefasciatus Mosquitoes, Haiti, 2016

Spondweni virus (SPONV) and Zika virus cause similar diseases in humans. We detected SPONV outside of Africa from a pool of Culex mosquitoes collected in Haiti in 2016. This finding raises questions about the role of SPONV as a human pathogen in Haiti and other Caribbean countries.

Multiplex real-time RT-PCR for detection and distinction of Spondweni and Zika virus

Zika (ZIKV) and Spondweni viruses (SPOV) are closely related mosquito borne flaviviruses in the Spondweni serogroup. The co-circulation and similar disease presentation following ZIKV and SPOV infection necessitates the development of a diagnostic tool for their simultaneous detection and distinction. We developed a one-step multiplex real-time RT-PCR (ZIKSPOV) to detect and distinguish between SPOV and ZIKV by utilizing a single primer set combined with virus specific hydrolysis probes. The ZIKSPOV assay was compared to published virus specific real-time RT-PCR assays and the limit of detection was comparable. The SPOV reference strain AR94 was detectable to 0.001 TCID₅₀ per PCR reaction, while African lineage ZIKV (MR 766) was detectable to 0.002 TCID₅₀ per reaction and Asian lineage ZIKV (H/PF/2013) to 0.05 TCID₅₀ per reaction. The ZIKSPOV assay did not detect other flaviviruses, indicative of its specificity for Spondweni serogroup. The ZIKSPOV assay is a useful addition to arbovirus diagnostic and surveillance tools in areas where ZIKV and SPOV are expected to co-circulate. Further evaluation is required to demonstrate the application of the assay for detection of ZIKV and SPOV in mosquito and human clinical samples.

Complete Genome Sequences of Spondweni Viruses Isolated between 1958 and 1960

Here, we report the complete genome sequences of 14 Spondweni viruses isolated in South Africa and Mozambique between 1958 and 1960. The sequences comprise 13 mosquito isolates and 1 human isolate following a documented laboratory infection. This study expands the publicly available data for this neglected virus from 4 to 18 sequences.

Mosquito-borne arboviruses of African origin: review of key viruses and vectors

Key aspects of 36 mosquito-borne arboviruses indigenous to Africa are summarized, including lesser or poorly-known viruses which, like Zika, may have the potential to escape current sylvatic cycling to achieve greater geographical distribution and medical importance. Major vectors are indicated as well as reservoir hosts, where known. A series of current and future risk factors is addressed. It is apparent that Africa has been the source of most of the major mosquito-borne viruses of medical importance that currently constitute serious global public health threats, but that there are several other viruses with potential for international challenge. The conclusion reached is that increased human population growth in decades ahead coupled with increased international travel and trade is likely to sustain and increase the threat of further geographical spread of current and new arboviral disease.

Pathogenesis and sexual transmission of Spondweni and Zika viruses

The Spondweni serogroup of viruses (Flaviviridae, Flavivirus) is comprised of Spondweni virus (SPONV) and Zika virus (ZIKV), which are mosquito-borne viruses capable of eliciting human disease. Numerous cases of ZIKV sexual transmission in humans have been documented following the emergence of the Asian genotype in the Americas. The African ZIKV genotype virus was previously implicated in the first reported case of ZIKV sexual transmission. Reports of SPONV infection in humans have been associated with non-specific febrile illness, but no association with sexual transmission has been reported. In order to assess the relative efficiency of sexual transmission of different ZIKV strains and the potential capacity of SPONV to be sexually transmitted, viral loads in the male reproductive tract and in seminal fluids were assessed in interferon α/β and –γ receptor deficient (AG129) mice. Male mice were inoculated subcutaneously with Asian genotype ZIKV strains PRVABC59 (Puerto Rico, 2015), FSS13025 (Cambodia, 2010), or P6-740 (Malaysia, 1966); African genotype ZIKV strain DakAr41524 (Senegal, 1984); or SPONV strain SAAr94 (South Africa, 1955). Infectious virus was detected in 60–72% of ejaculates collected from AG129 mice inoculated with ZIKV strains. In contrast, only 4% of ejaculates from SPONV-inoculated AG129 males were found to contain infectious virus, despite viral titers in the testes that were comparable to those of ZIKV-inoculated mice. Based on these results, future studies should be undertaken to assess the role of viral genetic determinants and host tropism that dictate the differential sexual transmission potential of ZIKV and SPONV.

The Spondweni serogroup of viruses, which includes Zika virus and Spondweni virus, are mosquito-borne viruses that can cause disease in humans. During the recent outbreak of Zika virus in the Americas, sexual transmission and in utero transmission have also been described. Due to the close genetic identity of Zika and Spondweni viruses, the herein reported study used a mouse model to assess the sexual transmission capacity of Spondweni virus in comparison to recent outbreak Zika strains and older Zika virus strains. In this model, all Zika strains were shed in seminal fluids from infected males. However, the percentage of ejaculates that contained infectious virus was significantly lower for Spondweni-infected males than Zika-infected males. Thus, sexual transmission potential is conserved among Zika viruses and not likely to fully explain the magnitude and dynamics of the recent outbreak in the Americas. In addition, sexual transmission potential should be further evaluated for Spondweni virus. Virus-specific differences in rates of shedding in seminal fluids will inform future studies on the viral determinants of sexual transmission.

Waiting in the wings: The potential of mosquito transmitted flaviviruses to emerge

The sudden dramatic emergence of the mosquito transmitted flavivirus Zika virus has bought to the world's attention a relatively obscure virus that was previously only known to specialist researchers. The genus Flavivirus of the family Flaviviridae contains a number of well-known mosquito transmitted human pathogenic viruses including the dengue, yellow fever, Japanese encephalitis and West Nile viruses. However, the genus also contains a number of lesser known human pathogenic viruses transmitted by mosquitoes including Wesselsbron virus, Ilheus virus, St. Louis encephalitis virus and Usutu virus. This review summarizes our knowledge of these lesser known mosquito transmitted flaviviruses and highlights their potential to emerge.

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.

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.

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.

Research and development of Zika virus vaccines

Zika virus (ZIKV) is a member of the family Flaviviridae, genus Flavivirus, and is transmitted by Aedes sp. mosquitoes. There are three genetic lineages of ZIKV: the East African, West African and Asian lineages. Until recently, Zika fever (ZF) has normally been considered a rare, mild febrile disease, but reports since 2012 have shown potentially severe complications associated with ZIKV infection, including microcephaly and Guillain-Barré syndrome. There are no licensed vaccines for ZIKV; however, many vaccine platforms/approaches that have been utilised for other flavivirus vaccines are being applied to ZIKV. Given the current outbreak of ZIKV in the Americas with its associated risks to pregnancy, we summarise what is known about the virus, how knowledge of currently licensed flavivirus vaccines can be applied to ZIKV vaccine development and the assessments of potential challenges for ZIKV vaccine testing and evaluation.

Zika Virus Targets Human STAT2 to Inhibit Type I Interferon Signaling

The ongoing epidemic of Zika virus (ZIKV) illustrates the importance of flaviviruses as emerging human pathogens. All vector-borne flaviviruses studied thus far have to overcome type I interferon (IFN) to replicate and cause disease in vertebrates. The mechanism(s) by which ZIKV antagonizes IFN signaling is unknown. Here, we report that the nonstructural protein NS5 of ZIKV and other flaviviruses examined could suppress IFN signaling, but through different mechanisms. ZIKV NS5 expression resulted in proteasomal degradation of the IFN-regulated transcriptional activator STAT2 from humans, but not mice, which may explain the requirement for IFN deficiency to observe ZIKV-induced disease in mice. The mechanism of ZIKV NS5 resembles dengue virus (DENV) NS5 and not its closer relative, Spondweni virus (SPOV). However, unlike DENV, ZIKV did not require the E3 ubiquitin ligase UBR4 to induce STAT2 degradation. Hence, flavivirus NS5 proteins exhibit a remarkable functional convergence in IFN antagonism, albeit by virus-specific mechanisms.

Zika virus infection-the next wave after dengue?

Zika virus was initially discovered in east Africa about 70 years ago and remained a neglected arboviral disease in Africa and Southeast Asia. The virus first came into the limelight in 2007 when it caused an outbreak in Micronesia. In the ensuing decade, it spread widely in other Pacific islands, after which its incursion into Brazil in 2015 led to a widespread epidemic in Latin America. In most infected patients the disease is relatively benign. Serious complications include Guillain-Barré syndrome and congenital infection which may lead to microcephaly and maculopathy. Aedes mosquitoes are the main vectors, in particular, Ae. aegypti. Ae. albopictus is another potential vector. Since the competent mosquito vectors are highly prevalent in most tropical and subtropical countries, introduction of the virus to these areas could readily result in endemic transmission of the disease. The priorities of control include reinforcing education of travellers to and residents of endemic areas, preventing further local transmission by vectors, and an integrated vector management programme. The container habitats of Ae. aegypti and Ae. albopictus means engagement of the community and citizens is of utmost importance to the success of vector control.

Arboviruses in southern Africa: are we missing something?

ABSTRACT 

The occurrence of the tick-borne zoonosis Crimean-Congo hemorrhagic fever is well established in South Africa. Similarly, mosquito-borne viruses Rift Valley fever, West Nile, Wesselsbron and Sindbis cause sporadic outbreaks. There is serological and/or virological evidence supporting the presence of lesser known arboviruses: the flaviviruses Usutu, Banzi and Spondweni, an Old World alphavirus Middelburg, orthobunyaviruses Germiston and Shuni and a tick-borne nairovirus, Dugbe. The medical significance of these viruses has not been established and lack of awareness and diagnostic capacity may lead to misdiagnosis. Historically, there have been outbreaks of chikungunya virus and dengue fever. This review focuses on arboviruses known to cause disease in South Africa or that have historically been shown to occur with potential for re-emergence.

Emerging viral threats in Gabon: health capacities and response to the risk of emerging zoonotic diseases in Central Africa

Emerging infectious diseases (EID) are currently the major threat to public health worldwide and most EID events have involved zoonotic infectious agents. Central Africa in general and Gabon in particular are privileged areas for the emergence of zoonotic EIDs. Indeed, human incursions in Gabonese forests for exploitation purposes lead to intensified contacts between humans and wildlife thus generating an increased risk of emergence of zoonotic diseases. In Gabon, 51 endemic or potential endemic viral infectious diseases have been reported. Among them, 22 are of zoonotic origin and involve 12 families of viruses. The most notorious are dengue, yellow fever, ebola, marburg, Rift Valley fever and chikungunya viruses. Potential EID due to wildlife in Gabon are thereby plentiful and need to be inventoried. The Gabonese Public Health system covers geographically most of the country allowing a good access to sanitary information and efficient monitoring of emerging diseases. However, access to treatment and prevention is better in urban areas where medical structures are more developed and financial means are concentrated even though the population is equally distributed between urban and rural areas. In spite of this, Gabon could be a good field for investigating the emergence or re-emergence of zoonotic EID. Indeed Gabonese health research structures such as CIRMF, advantageously located, offer high quality researchers and facilities that study pathogens and wildlife ecology, aiming toward a better understanding of the contact and transmission mechanisms of new pathogens from wildlife to human, the emergence of zoonotic EID and the breaking of species barriers by pathogens.

Genomics and evolution of Aedes-borne flaviviruses

We analysed the complete coding sequences of all recognized species of Aedes-borne flavivirus, including previously uncharacterized viruses within the yellow fever virus (YFV), Spondweni virus (SPOV) and dengue virus (DENV) groups. Two major phylogenetic lineages were revealed: one included the YFV and Entebbe bat virus groups, and the other included the DENV, SPOV and Culex-borne flavivirus groups. This analysis supported previous evidence that Culex-borne flaviviruses have evolved from ancestral Aedes-borne viruses. However, the topology at the junction between these lineages remains complex and may be refined by the discovery of viruses related to the Kedougou virus. Additionally, viral evolution was found to be associated with the appearance of new biological characteristics; mutations that may modify the envelope protein structure were identified for seven viruses within the YFV group, and an expansion of host-vector range was identified in the two major evolutionary lineages, which in turn may facilitate the emergence of mosquito-borne flaviviruses.