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.

Characterization of Two Highly Specific Monoclonal Antibodies Targeting the Glycan Loop of the Zika Virus Envelope Protein

Zika virus (ZIKV) is an emerging flavivirus associated with several neurological diseases such as Guillain-Barré syndrome in adults and microcephaly in newborn children. Its distribution and mode of transmission (via Aedes aegypti and Aedes albopictus mosquitoes) collectively cause ZIKV to be a serious concern for global health. High genetic homology of flaviviruses and shared ecology is a hurdle for accurate detection. Distinguishing infections caused by different viruses based on serological recognition can be misleading as many anti-flavivirus monoclonal antibodies (mAbs) discovered to date are highly cross-reactive, especially those against the envelope (E) protein. To provide more specific research tools, we produced ZIKV E directed hybridoma cell lines and characterized two highly ZIKV-specific mAb clones (mAbs A11 and A42) against several members of the Flavivirus genus. Epitope mapping of mAb A11 revealed glycan loop specificity in Domain I of the ZIKV E protein. The development of two highly specific mAbs targeting the surface fusion protein of ZIKV presents a significant advancement in research capabilities as these can be employed as essential tools to enhance our understanding of ZIKV identification on infected cells ex vivo or in culture.

Infection of Feral Phenotype Swine with Japanese Encephalitis Virus

Background: Japanese encephalitis virus (JEV) is a mosquito-borne zoonotic flavivirus and the leading cause of pediatric encephalitis in the Asian Pacific region. The transmission cycle primarily involves Culex spp. mosquitoes and Ardeid birds, with domestic pigs (Sus scrofa domestica) being the source of infectious viruses for the spillover of JEV from the natural endemic transmission cycle into the human population. Although many studies have concluded that domestic pigs play an important role in the transmission cycle of JEV, and infection of humans, the role of feral pigs in the transmission of JEV remains unclear. Since domestic and feral pigs are the same species, and because feral pig populations in the United States are increasing and expanding geographically, the current study aimed to test the hypothesis that if JEV were introduced into the United States, feral pigs might play a role in the transmission cycle. Materials and Methods: Sinclair miniature pigs, that exhibit the feral phenotype, were intradermally inoculated with JEV genotype Ib. These pigs were derived from crossing miniature domestic pig with four strains of feral pigs and were used since obtaining feral swine was not possible. Results: The Sinclair miniature pigs became viremic and displayed pathological outcomes similar to those observed in domestic swine. Conclusion: Based on these findings, we conclude that in the event of JEV being introduced into the United States, feral pig populations could contribute to establishment and maintenance of a transmission cycle of JEV and could lead to the virus becoming endemic in the United States.

Identification of the flavivirus conserved residues in the envelope protein hinge region for the rational design of a candidate West Nile live-attenuated vaccine

The flavivirus envelope protein is a class II fusion protein that drives flavivirus-cell membrane fusion. The membrane fusion process is triggered by the conformational change of the E protein from dimer in the virion to trimer, which involves the rearrangement of three domains, EDI, EDII, and EDIII. The movement between EDI and EDII initiates the formation of the E protein trimer. The EDI-EDII hinge region utilizes four motifs to exert the hinge effect at the interdomain region and is crucial for the membrane fusion activity of the E protein. Using West Nile virus (WNV) NY99 strain derived from an infectious clone, we investigated the role of eight flavivirus-conserved hydrophobic residues in the EDI-EDII hinge region in the conformational change of E protein from dimer to trimer and viral entry. Single mutations of the E-A54, E-I130, E-I135, E-I196, and E-Y201 residues affected infectivity. Importantly, the E-A54I and E-Y201P mutations fully attenuated the mouse neuroinvasive phenotype of WNV. The results suggest that multiple flavivirus-conserved hydrophobic residues in the EDI-EDII hinge region play a critical role in the structure-function of the E protein and some contribute to the virulence phenotype of flaviviruses as demonstrated by the attenuation of the mouse neuroinvasive phenotype of WNV. Thus, as a proof of concept, residues in the EDI-EDII hinge region are proposed targets to engineer attenuating mutations for inclusion in the rational design of candidate live-attenuated flavivirus vaccines.

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.

Comparison of Immunogenicity Between a Candidate Live Attenuated Vaccine and an Inactivated Vaccine for Cache Valley Virus

Cache Valley virus (CVV) is a mosquito-borne bunyavirus that is enzootic throughout the new world. Although CVV is known as an important agricultural pathogen, primarily associated with embryonic lethality and abortions in ruminants, it has recently been recognized for its expansion as a zoonotic pathogen. With the increased emergence of bunyaviruses with human and veterinary importance, there have been significant efforts dedicated to the development of bunyavirus vaccines. In this study, the immunogenicity of a candidate live-attenuated vaccine (LAV) for CVV, which contains the deletion of the nonstructural small (NSs) and nonstructural medium (NSm) genes (2delCVV), was evaluated and compared with an autogenous candidate vaccine created through the inactivation of CVV using binary ethylenimine (BEI) with an aluminum hydroxide adjuvant (BEI-CVV) in sheep. Both 2delCVV and BEI-CVV produced a neutralizing antibody response that exceeds the correlate of protection, that is, plaque reduction neutralization test titer >10. However, on day 63 postinitial immunization, 2delCVV was more immunogenic than BEI-CVV. These results warrant further development of 2delCVV as a candidate LAV and demonstrate that the double deletion of the NSs and NSm genes can be applied to the development of vaccines and as a common attenuation strategy for orthobunyaviruses.

Immunogenicity of a Candidate Live Attenuated Vaccine for Rift Valley Fever Virus with a Two-Segmented Genome

Rift Valley fever virus (RVFV) is an emerging arbovirus that affects both ruminants and humans. RVFV causes severe and recurrent outbreaks in Africa and the Arabian Peninsula with a significant risk for emergence into new locations. Although there are a variety of RVFV veterinary vaccines for use in endemic areas, there is currently no licensed vaccine for human use; therefore, there is a need to develop and assess new vaccines. Herein, we report a live-attenuated recombinant vaccine candidate for RVFV, based on the previously described genomic reconfiguration of the conditionally licensed MP12 vaccine. There are two general strategies used to develop live-attenuated RVFV vaccines, one being serial passage of wild-type RVFV strains to select attenuated mutants such as Smithburn, Clone 13, and MP12 vaccine strains. The second strategy has utilized reverse genetics to attenuate RVFV strains by introducing deletions or insertions within the viral genome. The novel candidate vaccine characterized in this report contains a two-segmented genome that lacks the medium viral segment (M) and two virulence genes (nonstructural small and nonstructural medium). The vaccine candidate, named r2segMP12, was evaluated for the production of neutralizing antibodies to RVFV in outbred CD-1 mice. The immune response induced by the r2segMP12 vaccine candidate was directly compared to the immune response induced by the rMP12 parental strain vaccine. Our study demonstrated that a single immunization with the r2segMP12 vaccine candidate at 10⁵ plaque-forming units elicited a higher neutralizing antibody response than the rMP12 vaccine at the same vaccination titer without the need for a booster.

SARS-CoV-2 and Arthropods: A Review

The emergence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) that led to the unprecedented COVID-19 pandemic exemplifies how a lack of understanding and preparedness for emerging viruses can result in consequences on a global scale. Statements that SARS-CoV-2 could not be transmitted by arthropod vectors were made without experimental support. Here we review laboratory-based research, field studies, and environmental studies to evaluate the potential for the virus to be transmitted either biologically or mechanically by arthropods. Based on these data, we conclude that transmission by arthropods is highly unlikely to play a significant epidemiological role in the transmission of SARS-CoV-2.

Inactivation of SARS-CoV-2 in All Blood Components Using Amotosalen/Ultraviolet A Light and Amustaline/Glutathione Pathogen Reduction Technologies

No cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transfusion-transmitted infections (TTI) have been reported. The detection of viral RNA in peripheral blood from infected patients and blood components from infected asymptomatic blood donors is, however, concerning. This study investigated the efficacy of the amotosalen/UVA light (A/UVA) and amustaline (S-303)/glutathione (GSH) pathogen reduction technologies (PRT) to inactivate SARS-CoV-2 in plasma and platelet concentrates (PC), or red blood cells (RBC), respectively. Plasma, PC prepared in platelet additive solution (PC-PAS) or 100% plasma (PC-100), and RBC prepared in AS-1 additive solution were spiked with SARS-CoV-2 and PR treated. Infectious viral titers were determined by plaque assay and log reduction factors (LRF) were determined by comparing titers before and after treatment. PR treatment of SARS-CoV-2-contaminated blood components resulted in inactivation of the infectious virus to the limit of detection with A/UVA LRF of >3.3 for plasma, >3.2 for PC-PAS-plasma, and >3.5 for PC-plasma and S-303/GSH LRF > 4.2 for RBC. These data confirm the susceptibility of coronaviruses, including SARS-CoV-2 to A/UVA treatment. This study demonstrates the effectiveness of the S-303/GSH treatment to inactivate SARS-CoV-2, and that PRT can reduce the risk of SARS-CoV-2 TTI in all blood components.

Treatment with dry hydrogen peroxide accelerates the decay of severe acute syndrome coronavirus-2 on non-porous hard surfaces

BACKGROUND

Disinfection of contaminated or potentially contaminated surfaces has become an integral part of the mitigation strategies for controlling coronavirus disease 2019. Whilst a broad range of disinfectants are effective in inactivating severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), application of disinfectants has a low throughput in areas that receive treatments. Disinfection of large surface areas often involves the use of reactive microbiocidal materials, including ultraviolet germicidal irradiation, chlorine dioxide, and hydrogen peroxide vapor. Albeit these methods are highly effective in inactivating SARS-CoV-2, the deployment of these approaches creates unacceptable health hazards and precludes the treatment of occupied indoor spaces using existing disinfection technologies. In this study, the feasibility of using dry hydrogen peroxide (DHP) in inactivating SARS-CoV-2 on contaminated surfaces in large indoor spaces was evaluated.

METHODS

Glass slides were inoculated with SARS-CoV-2 and treated with DHP between 5 and 25 ppb for up to 24 hours. Residual infectious virus samples were eluted from three replicates at each time point and titrated in African green monkey VeroE6 cells.

RESULTS

In comparison with the observed relatively high stability of SARS-CoV-2 on contaminated glass slides (control group), residual infectious titers of glass slides inoculated with SARS-CoV-2 were significantly reduced after receiving 120 minutes of DHP treatment.

CONCLUSIONS

The accelerated decay of SARS-CoV-2 on contaminated glass slides suggests that treatment with DHP can be an effective surface disinfection method for occupied indoor spaces.

Mosquito Saliva Modulates Japanese Encephalitis Virus Infection in Domestic Pigs

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that is the leading cause of pediatric viral encephalitis in Asia. Japanese encephalitis virus is transmitted by Culex species mosquitoes that also vector several zoonotic flaviviruses. Despite the knowledge that mosquito saliva contains molecules that may alter flavivirus pathogenesis, whether or not the deposition of viruses by infected mosquitoes has an impact on the kinetics and severity of JEV infection has not been thoroughly examined, especially in mammalian species involved in the enzootic transmission. Most JEV pathogenesis models were established using needle inoculation. Mouse models for West Nile (WNV) and dengue (DENV) viruses have shown that mosquito saliva can potentiate flavivirus infections and exacerbate disease symptoms. In this study, we determined the impact of mosquito salivary components on the pathogenesis of JEV in pigs, a species directly involved in its transmission cycle as an amplifying host. Interestingly, co-injection of JEV and salivary gland extract (SGE) collected from Culex quinquefasciatus produced milder febrile illness and shortened duration of nasal shedding but had no demonstrable impact on viremia and neuroinvasion. Our findings highlight that mosquito salivary components can differentially modulate the outcomes of flavivirus infections in amplifying hosts and in mouse models.

The Use of Arthropod-Borne Challenge Models in BSL-3Ag and BSL-4 Biocontainment

The study of many arthropod-borne pathogens requires high biosafety considerations, including the use of specialized facilities and equipment for arthropod containment. Mosquito- and tick-borne viruses such as yellow fever, West Nile, and Crimean Congo hemorrhagic fever viruses require facilities that are suitable for housing vertebrates. Multidisciplinary studies that incorporate the vector, vertebrate, and pathogens are essential for a complete understanding of the interactions between these transmission cycle components, especially if they aim to evaluate and model relative susceptibilities of different arthropods and vertebrates to infection and transmission between these. Under laboratory conditions, these studies can be relatively simple, for example, involving colonized arthropods, small animals, and attenuated viruses. Other studies are complex with large animals, high-biocontainment pathogens, and field-collected arthropods. These require a higher level of containment and special design considerations. Both of these types of experiments have their relative merits. A thorough understanding of the issues related to these types of studies and the benefits and drawbacks to using various challenge models will enable the researcher to develop realistic goals for various experiments. This review examines the varied issues that should be considered prior to starting these experiments and covers the basics from the procurement of various arthropods, rearing, high-containment facilities and operational issues specific to work with arthropods, types of infection experiments, and specific issues with arthropod and animal experiments in biosafety levels 3 and 4.

SARS-CoV-2 failure to infect or replicate in mosquitoes: an extreme challenge

This research addresses public speculation that SARS-CoV-2 might be transmitted by mosquitoes. The World Health Organization has stated “To date there has been no information nor evidence to suggest that the new coronavirus could be transmitted by mosquitoes”. Here we provide the first experimental data to investigate the capacity of SARS-CoV-2 to infect and be transmitted by mosquitoes. Three widely distributed species of mosquito; Aedes aegypti, Ae. albopictus and Culex quinquefasciatus, representing the two most significant genera of arbovirus vectors that infect people, were tested. We demonstrate that even under extreme conditions, SARS-CoV-2 virus is unable to replicate in these mosquitoes and therefore cannot be transmitted to people even in the unlikely event that a mosquito fed upon a viremic host.

The Intestinal Microbiome Restricts Alphavirus Infection and Dissemination through a Bile Acid-Type I IFN Signaling Axis

Chikungunya virus (CHIKV), an emerging alphavirus, has infected millions of people. However, the factors modulating disease outcome remain poorly understood. Here, we show in germ-free mice or in oral antibiotic-treated conventionally housed mice with depleted intestinal microbiomes that greater CHIKV infection and spread occurs within 1 day of virus inoculation. Alteration of the microbiome alters TLR7-MyD88 signaling in plasmacytoid dendritic cells (pDCs) and blunts systemic production of type I interferon (IFN). Consequently, circulating monocytes express fewer IFN-stimulated genes and become permissive for CHIKV infection. Reconstitution with a single bacterial species, Clostridium scindens, or its derived metabolite, the secondary bile acid deoxycholic acid, can restore pDC- and MyD88-dependent type I IFN responses to restrict systemic CHIKV infection and transmission back to vector mosquitoes. Thus, symbiotic intestinal bacteria modulate antiviral immunity and levels of circulating alphaviruses within hours of infection through a bile acid-pDC-IFN signaling axis, which affects viremia, dissemination, and potentially transmission.

A virus-like particle vaccine prevents equine encephalitis virus infection in nonhuman primates

Western, Eastern, and Venezuelan equine encephalitis viruses (WEEV, EEEV, and VEEV, respectively) are important mosquito-borne agents that pose public health and bioterrorism threats. Despite considerable advances in understanding alphavirus replication, there are currently no available effective vaccines or antiviral treatments against these highly lethal pathogens. To develop a potential countermeasure for viral encephalitis, we generated a trivalent, or three-component, EEV vaccine composed of virus-like particles (VLPs). Monovalent VLPs elicited neutralizing antibody responses and protected mice and nonhuman primates (NHPs) against homologous challenges, but they were not cross-protective. In contrast, NHPs immunized with trivalent VLPs were completely protected against aerosol challenge by each of these three EEVs. Passive transfer of IgG from immunized NHPs protected mice against aerosolized EEV challenge, demonstrating that the mechanism of protection was humoral. Because they are replication incompetent, these trivalent VLPs represent a potentially safe and effective vaccine that can protect against diverse encephalitis viruses.

Protection of swine by potent neutralizing anti-Japanese encephalitis virus monoclonal antibodies derived from vaccination

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus endemic in the Asia Pacific region. Despite use of several highly effective vaccines, it is estimated that up to 44,000 new cases of Japanese encephalitis (JE) occur every year including 14,000 deaths and 24,000 survivors with permanent sequelae. Humoral immunity induced by vaccination is critical for effective protection. Potently neutralizing antibodies reactive with the JEV envelope (E) protein are important since protective immune responses induced by both live-attenuated and inactivated JE vaccines target the E protein. Our understanding of how vaccine-induced humoral immunity protects vaccinees from morbidity and mortality is, however, limited and largely obtained from in vitro studies. With the exception of neurovirulence mouse models, very few platforms are available for evaluating the protective efficacy of neutralizing antibodies against JEV in vivo. Swine are a major amplifying host in the natural JEV transmission cycle and develop multiple pathological outcomes similar to humans infected with JEV. In this study, prophylactic passive immunization was performed in a miniature swine model, using two vaccination-induced monoclonal antibodies (mAb), JEV-31 and JEV-169. These were selected as representatives for antibodies reactive with the major antigenic structures in the E protein of JEV and related flaviviruses. JEV-31 recognizes the lateral ridge of E protein domain III (EDIII) whilst JEV-169 has a broad footprint of binding involving residues throughout domains I (EDI) and II (EDII) of the E protein. Detection of neutralizing antibodies in the serum of immunized animals mimics the presence of neutralizing antibodies in vaccinated individuals. Passive immunization with both mAbs significantly reduced the severity of diseases that resemble the symptoms of human JE including fever, viremia, viral shedding, systemic infection, and neuroinvasion. In contrast to the uniformed decrease of viral loads in lymphoid and central nervous systems, distinct kinetics in the onset of fever and viremia between animals receiving JEV-31 and JEV-169 suggest potential differences in immune protection mechanisms between anti-EDI and anti-EDIII neutralizing antibodies elicited by vaccination. Our data demonstrate the feasibility of using swine models in characterizing the protective humoral immunity against JEV and increase our understanding of how clonal populations of anti-E mAbs derived from JE vaccination protect against infection in vivo.

Infection and transmission of Cache Valley virus by Aedes albopictus and Aedes aegypti mosquitoes

Background

Cache Valley virus (CVV; Bunyavirales, Peribunyaviridae) is a mosquito-borne arbovirus endemic in North America. Although severe diseases are mainly observed in pregnant ruminants, CVV has also been recognized as a zoonotic pathogen that can cause fatal encephalitis in humans. Human exposures to CVV and its related subtypes occur frequently under different ecological conditions in the New World; however, neurotropic disease is rarely reported. High prevalence rates of neutralizing antibodies have been detected among residents in several Latin American cities. However, zoophilic mosquito species involved in the enzootic transmission are unlikely to be responsible for the transmission leading to human exposures to CVV. Mechanisms that lead to frequent human exposures to CVV remain largely unknown. In this study, competence of two anthropophilic mosquitoes, Aedes albopictus and Ae. aegypti, for CVV was determined using per os infection to determine if these species could play a role in the transmission of CVV in the domestic and peridomestic settings of urban and suburban areas.

Results

Aedes albopictus were highly susceptible to CVV whereas infection of Ae. aegypti occurred at a significantly lower frequency. Whilst the dissemination rates of CVV were comparable in the two species, the relatively long period to attain maximal infectious titer in Ae. aegypti demonstrated a significant difference in the replication kinetics of CVV in these species. Detection of viral RNA in saliva suggests that both Ae. albopictus and Ae. aegypti are competent vectors for CVV under laboratory conditions.

Conclusions

Differential susceptibility to CVV was observed in Ae. albopictus and Ae. aegypti, reflecting their relatively different capacities for vectoring CVV in nature. The high susceptibility of Ae. albopictus to CVV observed in this study suggests its potential role as an efficient vector for CVV. Complemented by the reports of multiple CVV isolates derived from Ae. albopictus, our finding provides the basis for how the dispersal of Ae. albopictus across the New World may have a significant impact on the transmission and ecology of CVV.

Simultaneous Coinfection of Macaques with Zika and Dengue Viruses Does not Enhance Acute Plasma Viremia but Leads to Activation of Monocyte Subsets and Biphasic Release of Pro-inflammatory Cytokines

The consequences of simultaneous infection with Zika (ZIKV) and Dengue (DENV) viruses are poorly understood. Here we show that rhesus macaques experimentally coinfected simultaneously with ZIKV and DENV-2 demonstrated ZIKV or DENV replication without an enhancement of either infection. Coinfection was accompanied by an increase in the proportions of CD14⁺CD16⁺ pro-inflammatory subsets of monocytes and release of pro-inflammatory cytokines in the plasma. Numerous cytokines such as I-TAC, Eotaxin, RANTES, MCP-1, IFNγ and MIG demonstrated a biphasic peak that coincided with the differences in kinetics of ZIKV and DENV replication suggesting that viral replication likely differentially modulated the release of these cytokines. Red blood cell indices significantly declined during acute infection suggesting transient anemia, and was accompanied by elevated levels of muscle, liver and renal injury markers. These findings have implications for understanding the pathogenesis of coinfection in ZIKV and DENV endemic regions, and is the 1^st report of an experimental coinfection using the rhesus macaque model for ZIKV and DENV infections.

Arbovirus-Mosquito Vector-Host Interactions and the Impact on Transmission and Disease Pathogenesis of Arboviruses

Hundreds of viruses, designated as arboviruses, are transmitted by arthropod vectors in complex transmission cycles between the virus, vertebrate host, and the vector. With millions of human and animal infections per year, it is critical to improve our understanding of the interactions between the biological and environmental factors that play a critical role in pathogenesis, disease outcomes, and transmission of arboviruses. This review focuses on mosquito-borne arboviruses and discusses current knowledge of the factors and underlying mechanisms that influence infection and transmission of arboviruses and discusses critical factors and pathways that can potentially become targets for intervention and therapeutics.

A Recombinant Subunit Based Zika Virus Vaccine Is Efficacious in Non-human Primates

Zika Virus (ZIKV), a virus with no severe clinical symptoms or sequelae previously associated with human infection, became a public health threat following an epidemic in French Polynesia 2013-2014 that resulted in neurological complications associated with infection. Although no treatment currently exists, several vaccines using different platforms are in clinical development. These include nucleic acid vaccines based on the prM-E protein from the virus and purified formalin-inactivated ZIKV vaccines (ZPIV) which are in Phase 1/2 clinical trials. Using a recombinant subunit platform consisting of antigens produced in Drosophila melanogaster S2 cells, we have previously shown seroconversion and protection against viremia in an immunocompetent mouse model. Here we demonstrate the efficacy of our recombinant subunits in a non-human primate (NHP) viremia model. High neutralizing antibody titers were seen in all protected macaques and passive transfer demonstrated that plasma from these NHPs was sufficient to protect against viremia in mice subsequently infected with ZIKV. Taken together our data demonstrate the immunogenicity and protective efficacy of the recombinant subunit vaccine candidate in NHPs as well as highlight the importance of neutralizing antibodies in protection against ZIKV infection and their potential implication as a correlate of protection.

Development of reverse genetics systems and investigation of host response antagonism and reassortment potential for Cache Valley and Kairi viruses, two emerging orthobunyaviruses of the Americas

Orthobunyaviruses such as Cache Valley virus (CVV) and Kairi virus (KRIV) are important animal pathogens. Periodic outbreaks of CVV have resulted in the significant loss of lambs on North American farms, whilst KRIV has mainly been detected in South and Central America with little overlap in geographical range. Vaccines or treatments for these viruses are unavailable. One approach to develop novel vaccine candidates is based on the use of reverse genetics to produce attenuated viruses that elicit immune responses but cannot revert to full virulence. The full genomes of both viruses were sequenced to obtain up to date genome sequence information. Following sequencing, minigenome systems and reverse genetics systems for both CVV and KRIV were developed. Both CVV and KRIV showed a wide in vitro cell host range, with BHK-21 cells a suitable host cell line for virus propagation and titration. To develop attenuated viruses, the open reading frames of the NSs proteins were disrupted. The recombinant viruses with no NSs protein expression induced the production of type I interferon (IFN), indicating that for both viruses NSs functions as an IFN antagonist and that such attenuated viruses could form the basis for attenuated viral vaccines. To assess the potential for reassortment between CVV and KRIV, which could be relevant during vaccination campaigns in areas of overlap, we attempted to produce M segment reassortants by reverse genetics. We were unable to obtain such viruses, suggesting that it is an unlikely event.

Culex tarsalis is a competent vector species for Cache Valley virus

BACKGROUND

Cache Valley virus (CVV) is a mosquito-borne orthobunyavirus endemic in North America. The virus is an important agricultural pathogen leading to abortion and embryonic lethality in ruminant species, especially sheep. The importance of CVV in human public health has recently increased because of the report of severe neurotropic diseases. However, mosquito species responsible for transmission of the virus to humans remain to be determined. In this study, vector competence of three Culex species mosquitoes of public health importance, Culex pipiens, Cx. tarsalis and Cx. quinquefasciatus, was determined in order to identify potential bridge vector species responsible for the transmission of CVV from viremic vertebrate hosts to humans.

RESULTS

Variation of susceptibility to CVV was observed among selected Culex species mosquitoes tested in this study. Per os infection resulted in the establishment of infection and dissemination in Culex tarsalis, whereas Cx. pipiens and Cx. quinquefasciatus were highly refractory to CVV. Detection of viral RNA in saliva collected from infected Cx. tarsalis provided evidence supporting its role as a competent vector.

CONCLUSIONS

Our study provided further understanding of the transmission cycles of CVV and identifies Cx. tarsalis as a competent vector.

North American Culex pipiens and Culex quinquefasciatus are competent vectors for Usutu virus

Background

Usutu virus (USUV) is a member of the Japanese encephalitis virus (JEV) serocomplex in the Flaviviridae family. Emergence of USUV in Europe has led to disease burdens in birds and created increasing concern for the potential zoonotic transmission to humans. Whilst USUV has not been detected in the New World, the identification of competent vector species in North America is critical in the assessment of the likelihood of its dispersal and establishment of enzootic transmission cycles. The objective of this study was to determine vector competence of potential mosquito vectors in North America for USUV. Three medically important mosquito species were selected for testing because of their involvement in the transmission of West Nile virus and St. Louis encephalitis virus, two related JEV serocomplex flaviviruses in the New World.

Methodology/Principal findings

Oral challenge of Culex pipiens, Culex quinquefasciatus, and Aedes albopictus was performed to determine the susceptibility and vector competence of North American mosquitoes for USUV. Infection status was monitored by the isolation of virus from homogenized mosquito tissues. The disseminated form of infection was demonstrated by the detection of infectious virus in the head, wings, and legs of infected mosquitoes. The presence of viral RNA in saliva of infected Cx. pipiens and Cx. quinquefasciatus indicated that both species are competent for transmission of USUV.

Conclusions/Significance

Results indicate that members of the Cx. pipiens complex are susceptible to USUV and competent for its transmission potential in North America in the event of its introduction. In contrast, Ae. albopictus were highly refractory to USUV infection, suggesting that this species is unlikely to contribute to USUV transmission in North America.

Usutu virus is an emerging mosquito-borne flavivirus maintained between avian and mosquito species. Although the pathogen has only been detected in Africa and Europe, a growing concern of its dispersal and zoonotic potential warrants the investigation on the vector competence of mosquito species outside the endemic regions for USUV. Identification of species involved in the transmission cycles allows for the formulation of disease control strategies such as vector control. As observed with West Nile virus and Japanese encephalitis virus, the presence of competent vector species is critical for the establishment of enzootic transmission cycles and contributes to the viral maintenance in nature. Despite differences in the genetics and bionomics of Culex pipiens in the Old World, members of the Cx. pipiens species in the New World are competent for USUV based on the results of per os challenges performed in this study. Cx. pipiens and Cx. quinquefasciatus are capable of initiating enzootic transmission cycles in the presence of susceptible avian species and should be targeted for vector control in the event of a disease outbreak.

Zika convalescent macaques display delayed induction of anamnestic cross-neutralizing antibody responses after dengue infection

Structural similarities between Zika (ZIKV) and dengue virus (DENV) leads to the induction of cross-reactive responses. We have previously demonstrated that ZIKV exposed macaques significantly enhance DENV viremia. Here we show that this enhancement of DENV infection occurred in the presence of high levels of DENV cross-reactive IgG1 subclass of binding antibodies (bAb) with low DENV neutralizing antibody (nAb) activity (<1:10). The DENV-2 nAb titres after ZIKV infection were, however, higher than those induced in DENV-2 only infected animals suggesting that ZIKV induced low titres of cross-nAb against DENV. Surprisingly, DENV-2 infection of animals previously infected with ZIKV was not accompanied by an anamnestic increase in cross-nAb titres till about 1 week after DENV-2 infection. This delay coincided with enhanced DENV-2 viremia indicating that high levels of cross-bAb in the absence of high nAb contributes to enhancement of DENV infection. Serum collected 8 weeks after DENV-2 infection had high levels of nAb and showed delayed antibody dependent enhancement (ADE) of infection (1:100 dilution) as compared with serum that was collected from ZIKV infected animals prior to DENV-2 infection (1:10 dilution). Examination of serum from macaques that were simultaneously infected with both ZIKV and DENV-2 showed high levels of nAb and delayed ADE responses raising the possibility that the low levels of cross-nAb induced by ZIKV infection could be overcome by co-immunization against ZIKV and DENV infection. Taken together, our results provide additional insights into the nature and kinetics of cross-reactive antibody responses and identify a critical correlate that could potentially prevent enhancement of DENV infection during ZIKV convalescence.

Shedding of Japanese Encephalitis Virus in Oral Fluid of Infected Swine

Japanese encephalitis virus (JEV) is a zoonotic mosquito-borne flavivirus endemic in the Asia-Pacific region. Maintenance of JEV in nature involves enzootic transmission by competent Culex mosquitoes among susceptible avian and swine species. Historically, JEV has been regarded as one of the most important arthropod-borne viruses in Southeast Asia. Oronasal shedding of JEV from infected amplification hosts was not recognized until the recent discovery of vector-free transmission of JEV among domestic pigs. In this study, oral shedding of JEV was characterized in domestic pigs and miniature swine representing the feral phenotype. A rope-based sampling method followed by the detection of viral RNA using RT-qPCR allowed the collection and detection of JEV in oral fluid samples collected from intradermally challenged animals. The results suggest that the shedding of JEV in oral fluid can be readily detected by molecular diagnostic assays at the acute phase of infection. It also demonstrates the feasibility of this technique for the diagnosis and surveillance of JEV in swine species.

Application of a Nonpaper Based Matrix to Preserve Chikungunya Virus Infectivity at Ambient Temperature

For over 100 years, field studies on arboviruses and the subsequent delivery and administration of live attenuated vaccines have been complicated by the need to maintain a so-called "cold chain," which is the source to destination refrigeration of biological materials. In this study we describe the application of a nonpaper based matrix and demonstrate preservation of chikungunya virus infectivity at ambient temperature for 7 days. The technique was successfully employed using infectious cell culture medium and infected mosquito homogenate samples. This technique provides a simple solution for conducting studies in resource-limited areas, where the maintenance of a cold chain is technically challenging.

Prior Exposure to Zika Virus Significantly Enhances Peak Dengue-2 Viremia in Rhesus Macaques

Structural and functional homologies between the Zika and Dengue viruses’ envelope proteins raise the possibility that cross-reactive antibodies induced following Zika virus infection might enhance subsequent Dengue infection. Using the rhesus macaque model we show that prior infection with Zika virus leads to a significant enhancement of Dengue-2 viremia that is accompanied by neutropenia, lympocytosis, hyperglycemia, and higher reticulocyte counts, along with the activation of pro-inflammatory monocyte subsets and release of inflammatory mediators. Zika virus infection induced detectable Dengue cross-reactive serum IgG responses that significantly amplified after Dengue-2 virus infection. Serum from Zika virus immune animals collected prior to Dengue-2 infection showed significant capacity for in vitro antibody dependent enhancement of Dengue-1, 2, 3 and 4 serotypes suggesting that pre-existing immunity to Zika virus could potentially enhance infection by heterologous Dengue serotypes. Our results provide first in vivo evidence that prior exposure to Zika virus infection can enhance Dengue infection, which has implications for understanding pathogenesis and the development of vaccines.

Rapid development of a DNA vaccine for Zika virus

Zika virus (ZIKV) was identified as a cause of congenital disease during the explosive outbreak in the Americas and Caribbean that began in 2015. Because of the ongoing fetal risk from endemic disease and travel-related exposures, a vaccine to prevent viremia in women of childbearing age and their partners is imperative. We found that vaccination with DNA expressing the premembrane and envelope proteins of ZIKV was immunogenic in mice and nonhuman primates, and protection against viremia after ZIKV challenge correlated with serum neutralizing activity. These data not only indicate that DNA vaccination could be a successful approach to protect against ZIKV infection, but also suggest a protective threshold of vaccine-induced neutralizing activity that prevents viremia after acute infection.

Aedes albopictus (Diptera: Culicidae) and Mosquito-Borne Viruses in the United States

The Asian tiger mosquito Aedes albopictus (Skuse), is a highly invasive species that continues to expand its geographic distribution both in the United States and in countries on other continents. Studies have demonstrated its susceptibility to infection with at least 32 viruses, including 13 that are present in the United States. Despite this susceptibility, its role as a significant competent vector in natural transmission cycles of arboviruses, has been limited. However, with the recent introductions of chikungunya and Zika viruses into the Americas, for which Ae. albopictus is a recognized vector, it is possible that the species may contribute to the transmission of these viruses to humans and perhaps other susceptible vertebrates.

Susceptibility of a North American Culex quinquefasciatus to Japanese Encephalitis Virus

Japanese encephalitis virus (JEV) is a flavivirus that is transmitted by Culex (Cx.) tritaeniorhynchus in tropical and subtropical regions of Asia. The endemic transmission cycle involves domestic pigs and avian species that serve as amplification hosts; humans are incidental hosts that cannot develop a high-titer viremia sufficient for mosquito infection. Although vaccination can be an effective strategy for disease prevention and is used extensively in multiple Asian countries, unvaccinated immunologically naïve human populations can suffer from severe neurological sequelae. The potential introduction of JEV into North America would be a major threat to human and animal health. In this study, field-collected Cx. quinquefasciatus from Valdosta, Georgia, were tested for their susceptibility to JEV and their potential to develop a disseminated infection via per os infection. These results demonstrate that North American Cx. quinquefasciatus are susceptible to JEV infection and subsequent dissemination at 14 days post infection (d.p.i.). Detection of viral RNA in saliva from infected mosquitoes also indicates competent vectors for JEV can be found in North America.

A novel mosquito ubiquitin targets viral envelope protein for degradation and reduces virion production during dengue virus infection

Background

Dengue virus (DENV) is a mosquito-borne flavivirus that causes significant human disease and mortality in the tropics and subtropics. By examining the effects of virus infection on gene expression, and interactions between virus and vector, new targets for prevention of infection and novel treatments may be identified in mosquitoes. We previously performed a microarray analysis of the Aedes aegypti transcriptome during infection with DENV and found that mosquito ubiquitin protein Ub3881 (AAEL003881) was specifically and highly down-regulated. Ubiquitin proteins have multiple functions in insects, including marking proteins for proteasomal degradation, regulating apoptosis and mediating innate immune signaling.

Methods

We used qRT-PCR to quantify gene expression and infection, and RNAi to reduce Ub3881 expression. Mosquitoes were infected with DENV through blood feeding. We transfected DENV protein expression constructs to examine the effect of Ub3881 on protein degradation. We used site-directed mutagenesis and transfection to determine what amino acids are involved in Ub3881-mediated protein degradation. Immunofluorescence, Co-immunoprecipitation and Western blotting were used to examine protein interactions and co-localization.

Results

The overexpression of Ub3881, but not related ubiquitin proteins, decreased DENV infection in mosquito cells and live Ae. aegypti. The Ub3881 protein was demonstrated to be involved in DENV envelope protein degradation and reduce the number of infectious virions released.

Conclusions

We conclude that Ub3881 has several antiviral functions in the mosquito, including specific viral protein degradation.

General significance

Our data highlights Ub3881 as a target for future DENV prevention strategies in the mosquito transmission vector.

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A novel mosquito ubiquitin, Ub3881, is identified in Aedes aegypti.

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Ub3881 is shown to have antiviral functions during dengue virus infection of the mosquito.

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Ub3881 targets a dengue viral protein for degradation during infection.

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Future dengue virus prevention strategies could incorporate Ub3881 as a target to prevent mosquito infection.

The potential for the establishment of new arbovirus transmission cycles in Europe

Mosquito-borne viruses are an increasing health threat to humans, and potentially other vertebrates, in areas where they have not previously existed or from which they had been eradicated. Chikungunya virus emergence exemplifies how multiple factors can act synergistically resulting in rapid, large-scale redistribution and establishment. Despite our increased capacity to collect and analyze large amounts of data, we still lack epidemiological models to facilitate accurate predictions of when and where new diseases may occur. Models focusing on climate changes may have long-term value; however, there is an urgent need for mathematical modeling of viral epidemiology to enable forecasting immediate or near-term threats.

Chikungunya virus transmission potential by local Aedes mosquitoes in the Americas and Europe

Background

Chikungunya virus (CHIKV), mainly transmitted in urban areas by the mosquitoes Aedes aegypti and Aedes albopictus, constitutes a major public health problem. In late 2013, CHIKV emerged on Saint-Martin Island in the Caribbean and spread throughout the region reaching more than 40 countries. Thus far, Ae. aegypti mosquitoes have been implicated as the sole vector in the outbreaks, leading to the hypothesis that CHIKV spread could be limited only to regions where this mosquito species is dominant.

Methodology/Principal Findings

We determined the ability of local populations of Ae. aegypti and Ae. albopictus from the Americas and Europe to transmit the CHIKV strain of the Asian genotype isolated from Saint-Martin Island (CHIKV_SM) during the recent epidemic, and an East-Central-South African (ECSA) genotype CHIKV strain isolated from La Réunion Island (CHIKV_LR) as a well-characterized control virus. We also evaluated the effect of temperature on transmission of CHIKV_SM by European Ae. albopictus. We found that (i) Aedes aegypti from Saint-Martin Island transmit CHIKV_SM and CHIKV_LR with similar efficiency, (ii) Ae. aegypti from the Americas display similar transmission efficiency for CHIKV_SM, (iii) American and European populations of the alternative vector species Ae. albopictus were as competent as Ae. aegypti populations with respect to transmission of CHIKV_SM and (iv) exposure of European Ae. albopictus to low temperatures (20°C) significantly reduced the transmission potential for CHIKV_SM.

Conclusions/Significance

CHIKV strains belonging to the ECSA genotype could also have initiated local transmission in the new world. Additionally, the ongoing CHIKV outbreak in the Americas could potentially spread throughout Ae. aegypti- and Ae. albopictus-infested regions of the Americas with possible imported cases of CHIKV to Ae. albopictus-infested regions in Europe. Colder temperatures may decrease the local transmission of CHIKV_SM by European Ae. albopictus, potentially explaining the lack of autochthonous transmission of CHIKV_SM in Europe despite the hundreds of imported CHIKV cases returning from the Caribbean.

More than one million chikungunya cases have been reported in the Americas since October 2013, when the Asian genotype of chikungunya virus (CHIKV) was imported by a traveller returning from Asia. CHIKV is mainly transmitted in urban areas by the domestic mosquitoes Aedes aegypti and Aedes albopictus. In this study, we evaluate the potential for the CHIKV circulating in the Caribbean to initiate outbreaks in Aedes-infested regions of continental America and Europe by assessing the ability of local mosquitoes to experimentally transmit the virus. Mosquitoes were exposed to a blood-meal containing the virus which must overcome several barriers to infect various tissues in the vector before being secreted in the mosquito saliva when biting a host. We found that Ae. aegypti and Ae. albopictus transmitted similarly the virus. When exposing Ae. albopictus from Europe at a temperature of 20°C after infection, we detect a significant drop of CHIKV transmission potential. Our results suggest that the CHIKV outbreak in the Americas could potentially spread throughout Ae. aegypti- and Ae. albopictus-infested regions of the Americas however with a limited risk of spillovers in Ae. albopictus-infested regions in Europe. These data will be useful for adapting vector control strategies and epidemiological surveillance.

Evaluation of Simultaneous Transmission of Chikungunya Virus and Dengue Virus Type 2 in Infected Aedes aegypti and Aedes albopictus (Diptera: Culicidae)

The simultaneous transmission of chikungunya virus (CHIKV) and dengue viruses (DENV) has been a major public health concern because of their sympatric distribution and shared mosquito vectors. Groups of Aedes aegypti (L.) and Aedes albopictus (Skuse) were orally infected with 1.5 × 10(5) PFU/ml of CHIKV and 3.2 × 10(6) FFU/ml of DENV-2 simultaneously or separately in inverse orders and evaluated for dissemination and transmission by qRT-PCR. Simultaneous dissemination of both viruses was detected for all groups in Ae. aegypti and Ae. albopictus while cotransmission of CHIKV and DENV-2 only occurred at low rates after sequential but not simultaneous infection.

pH-Dependent entry of chikungunya virus fusion into mosquito cells

BACKGROUND

Millions of human infections caused by arthropod-borne pathogens are initiated by the feeding of an infected mosquito on a vertebrate. However, interactions between the viruses and the mosquito vector, which facilitates successful infection and transmission of virus to a subsequent vertebrate host, are still not fully understood.

FINDING

Here we describe early chikungunya virus (CHIKV) infectious events in cells derived from one of the most important CHIKV vectors, Aedes albopictus. We demonstrated that CHIKV infection of mosquito cells depended on acidification of the endosome as indicated by significant inhibition following prophylactic treatment with the lysosomotropic drugs chloroquine, ammonium chloride, and monensin, which is consistent with observations in mammalian cells. While all three agents inhibited CHIKV infection in C6/36 cells, ammonium chloride was less toxic to cells than the other agents.

CONCLUSION

The observation of similar mechanisms for inhibition of CHIKV infection in mosquito and mammalian cell lines suggests that conserved entry pathways are utilized by CHIKV for vertebrate and invertebrate cell types.

Flavivirus-mosquito interactions

The Flavivirus genus is in the family Flaviviridae and is comprised of more than 70 viruses. These viruses have a broad geographic range, circulating on every continent except Antarctica. Mosquito-borne flaviviruses, such as yellow fever virus, dengue virus serotypes 1-4, Japanese encephalitis virus, and West Nile virus are responsible for significant human morbidity and mortality in affected regions. This review focuses on what is known about flavivirus-mosquito interactions and presents key data collected from the field and laboratory-based molecular and ultrastructural evaluations.

Deliberate attenuation of chikungunya virus by adaptation to heparan sulfate-dependent infectivity: a model for rational arboviral vaccine design

Mosquito-borne chikungunya virus (CHIKV) is a positive-sense, single-stranded RNA virus from the genus Alphavirus, family Togaviridae, which causes fever, rash and severe persistent polyarthralgia in humans. Since there are currently no FDA licensed vaccines or antiviral therapies for CHIKV, the development of vaccine candidates is of critical importance. Historically, live-attenuated vaccines (LAVs) for protection against arthropod-borne viruses have been created by blind cell culture passage leading to attenuation of disease, while maintaining immunogenicity. Attenuation may occur via multiple mechanisms. However, all examined arbovirus LAVs have in common the acquisition of positively charged amino acid substitutions in cell-surface attachment proteins that render virus infection partially dependent upon heparan sulfate (HS), a ubiquitously expressed sulfated polysaccharide, and appear to attenuate by retarding dissemination of virus particles in vivo. We previously reported that, like other wild-type Old World alphaviruses, CHIKV strain, La Réunion, (CHIKV-LR), does not depend upon HS for infectivity. To deliberately identify CHIKV attachment protein mutations that could be combined with other attenuating processes in a LAV candidate, we passaged CHIKV-LR on evolutionarily divergent cell-types. A panel of single amino acid substitutions was identified in the E2 glycoprotein of passaged virus populations that were predicted to increase electrostatic potential. Each of these substitutions was made in the CHIKV-LR cDNA clone and comparisons of the mutant viruses revealed surface exposure of the mutated residue on the spike and sensitivity to competition with the HS analog, heparin, to be primary correlates of attenuation in vivo. Furthermore, we have identified a mutation at E2 position 79 as a promising candidate for inclusion in a CHIKV LAV.

With the adaptation of chikungunya virus (CHIKV) to transmission by the Aedes albopictus mosquito, a pandemic has occurred resulting in four to six million human infections, and the virus continues to become endemic in new regions, most recently in the Caribbean. CHIKV can cause debilitating polyarthralgia, lasting for weeks to years, and there are currently no licensed vaccines or antiviral therapies available. While an investigational live-attenuated vaccine (LAV) exists, problems with reactogenicity have precluded its licensure. The purpose of the current study was to: i) devise an in vitro passage procedure that reliably generates a panel of CHIKV envelope glycoprotein mutations for screening as vaccine candidates; ii) determine the position of the mutations in the three-dimensional structure of the alphavirus spike complex and their effect on electrostatic potential; iii) determine the attenuation characteristics of each mutation in a murine model of CHIKV musculoskeletal disease; and iv) to identify in vitro assays examining the dependency of infection upon HS that correlate with attenuation and localization in the glycoprotein spike. This approach provides a paradigm for the rational design of future LAVs for CHIKV and other mosquito-borne viruses, by deliberately selecting and combining attenuating processes.

Photochemical inactivation of chikungunya virus in human apheresis platelet components by amotosalen and UVA light

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that recently re-emerged in Africa and rapidly spread into countries of the Indian Ocean basin and South-East Asia. The mean viremic blood donation risk for CHIKV on La Réunion reached 1.5% at the height of the 2005-2006 outbreaks, highlighting the need for development of safety measures to prevent transfusion-transmitted infections. We describe successful inactivation of CHIKV in human platelets and plasma using photochemical treatment with amotosalen and long wavelength UVA illumination. Platelet components in additive solution and plasma units were inoculated with two different strains of high titer CHIKV stock (6.0-8.0 logs/mL), and then treated with amotosalen and exposure to 1.0-3.0 J/cm² UVA. Based on in vitro assays of infectious virus pre- and post-treatment to identify endpoint dilutions where virus was not detectable, mean viral titers could effectively be reduced by > 6.4 ± 0.6 log₁₀ TCID₅₀/mL in platelets and ≥ 7.6 ± 1.4 logs in plasma, indicating this treatment has the capacity to prevent CHIKV transmission in human blood components collected from infected donors in or traveling from areas of CHIKV transmission.

Infection of Aedes albopictus with chikungunya virus rectally administered by enema

Chikungunya virus (CHIKV) is an alphavirus transmitted by Aedes albopictus and Aedes aegypti mosquitoes in tropical areas of Africa, Asia, and the islands of the Indian Ocean. In 2007 and 2009, CHIKV was transmitted outside these tropical areas and caused geographically localized infections in people in Italy and France. To temporally and spatially characterize CHIKV infection of Ae. albopictus midguts, a comparison of viral distribution in mosquitoes infected per os or by enema was conducted. Ae. albopictus infected with CHIKV LR 5' green fluorescent protein (GFP) at a titer 10(6.95) tissue culture infective dose(50) (TCID(50))/mL, were collected and analyzed for virus dissemination by visualizing GFP expression and titration up to 14 days post inoculation (dpi). Additionally, midguts were dissected from the mosquitoes and imaged by fluorescence microscopy for comparison of midgut infection patterns between orally- and enema-infected mosquitoes. When virus was delivered via enema, the anterior midgut appeared more readily infected by 3 dpi, with increased GFP presentation observed in this same location of the midgut at 7 and 14 dpi when compared to orally-infected mosquitoes. This work demonstrates that enema delivery of virus is a viable technique for use of mosquito infection. Enema injection of mosquitoes may be an alternative to intrathoracic inoculation because the enema delivery more closely models natural infection and neither compromises midgut integrity nor involves a wound that can induce immune responses. Furthermore, unlike intrathoracic delivery, the enema does not bypass midgut barriers to infect tissues artificially in the hemocoel of the mosquito.

Photochemical inactivation of chikungunya virus in plasma and platelets using the Mirasol pathogen reduction technology system

BACKGROUND

Chikungunya virus (CHIKV) is a reemerging mosquito-borne virus that has been responsible for a number of large-scale epidemics as well as imported cases covering a wide geographical range. As a blood-borne virus capable of mounting a high-titer viremia in infected humans, CHIKV was included on a list of risk agents for transfusion and organ transplant by the AABB Transfusion-Transmitted Diseases Committee. Therefore, we evaluated the ability of the Mirasol pathogen reduction technology (PRT) system (CaridianBCT Biotechnologies) to inactivate live virus in contaminated plasma and platelet (PLT) samples.

STUDY DESIGN AND METHODS

Plasma, PLTs, and phosphate-buffered saline controls were spiked with CHIKV and treated with riboflavin and varying doses of ultraviolet (UV) light using the Mirasol PRT system. Samples were tested before and after treatment for cytotoxicity, interference, and virus titer by titration and quantitative real-time reverse transcription-polymerase chain reaction.

RESULTS

A significant reduction in CHIKV titer of greater than 99% was recorded after treatment of plasma or PLTs with the Mirasol PRT system, and the titer reduction was directly proportional to the UV dose delivered to the samples. No cytotoxicity of interference was observed in any sample at any treatment dose.

CONCLUSION

These data indicate that the Mirasol PRT system efficiently inactivated live CHIKV in plasma and PLTs and could therefore potentially be used to prevent CHIKV transmission through the blood supply.