Chimeric Sindbis/eastern equine encephalitis vaccine candidates are highly attenuated and immunogenic in mice

Phagocyte-expressed glycosaminoglycans promote capture of alphaviruses from the blood circulation in a host species-specific manner

The magnitude and duration of vertebrate viremia are critical determinants of arbovirus transmission, geographic spread, and disease severity-yet, mechanisms determining arbovirus viremia levels are poorly defined. Previous studies have drawn associations between in vitro virion-glycosaminoglycan (GAG) interactions and in vivo clearance kinetics of virions from blood circulation. From these observations, it is commonly hypothesized that GAG-binding virions are rapidly removed from circulation due to ubiquitous expression of GAGs by vascular endothelial cells, thereby limiting viremia. Using an in vivo model for viremia, we compared the vascular clearance of low and enhanced GAG-binding viral variants of chikungunya, eastern- (EEEV), and Venezuelan- (VEEV) equine encephalitis viruses. We find GAG-binding virions are more quickly removed from circulation than their non-GAG-binding variant; however individual clearance kinetics vary between GAG-binding viruses, from swift (VEEV) to slow removal from circulation (EEEV). Remarkably, we find phagocytes are required for efficient vascular clearance of some enhanced GAG-binding virions. Moreover, transient depletion of vascular heparan sulfate impedes vascular clearance of only some GAG-binding viral variants and in a phagocyte-dependent manner, implying phagocytes can mediate vascular GAG-virion interactions. Finally, in direct contrast to mice, we find enhanced GAG-binding EEEV is resistant to vascular clearance in avian hosts, suggesting the existence of species-specificity in virion-GAG interactions. In summary, these data support a role for GAG-mediated clearance of some viral particles from the blood circulation, illuminate the potential of blood-contacting phagocytes as a site for GAG-virion binding, and suggest a role for species-specific GAG structures in arbovirus ecology.

Inactivation of highly transmissible livestock and avian viruses including influenza A and Newcastle disease virus for molecular diagnostics

There is a critical need for an inactivation method that completely inactivates pathogens at the time of sample collection while maintaining the nucleic acid quality required for diagnostic PCR testing. This inactivation method is required to alleviate concerns about transmission potential, minimize shipping complications and cost, and enable testing in lower containment laboratories, thereby enhancing disease diagnostics through improved turn-around time. This study evaluated a panel of 10 surrogate viruses that represent highly pathogenic animal diseases. These results showed that a commercial PrimeStore® molecular transport media (PSMTM) completely inactivated all viruses tested by >99.99%, as determined by infectivity and serial passage assays. However, the detection of viral nucleic acid by qRT-PCR was comparable in PSMTM and control-treated conditions. These results were consistent when viruses were evaluated in the presence of biological material such as sera and cloacal swabs to mimic diagnostic sample conditions for non-avian and avian viruses, respectively. The results of this study may be utilized by diagnostic testing laboratories for highly pathogenic agents affecting animal and human populations. These results may be used to revise guidance for select agent diagnostic testing and the shipment of infectious substances.

Chimeric Viruses Containing Select Agents: The Biology Behind Their Creation, Attenuation, and Exclusion From Regulation

The US Centers for Disease Control and Prevention (CDC), as part of the Federal Select Agent Program, and under the purview of 42 CFR §73.3, has the ability to regulate chimeric viruses that contain portions of pathogens that are part of the select agents and toxins list. In addition, the CDC is responsible for excluding pathogens from regulation, including chimeric viruses, that are sufficiently attenuated. Since 2003, the CDC has excluded over 20 chimeric viruses that contain portions of select agents. But in late 2021, the CDC proposed a regulatory first-the addition of a chimeric virus to the select agents and toxins list. To better understand the importance and applicability of this action, we surveyed the landscape of previous exclusions from select agent regulation. First, we reviewed the exclusion criteria used by the Intragovernmental Select Agents and Toxins Technical Advisory Committee in their advisement of the Federal Select Agent Program. We then reviewed the literature on chimeric viruses that contain portions of select agents and that have been excluded from regulation due to sufficient attenuation, focusing on chimeric alphaviruses and chimeric avian influenza viruses. By analyzing biological commonalities and patterns in the structure and methodology of the development of previously excluded chimeric viruses, we provide insight into how the CDC has used exclusion criteria in the past to regulate chimeric viruses. We conclude by contrasting previous exclusions with the recent addition of SARS-CoV-1/SARS-CoV-2 chimeric viruses to the select agents and toxins list, demonstrating that this addition strays from established, effective regulatory processes, and is thus a regulatory misstep.

Phagocyte-expressed glycosaminoglycans promote capture of alphaviruses from the blood circulation in a host species-specific manner

The magnitude and duration of vertebrate viremia are critical determinants of arbovirus transmission, geographic spread, and disease severity-yet, mechanisms determining arbovirus viremia levels are poorly defined. Previous studies have drawn associations between in vitro virion-glycosaminoglycan (GAG) interactions and in vivo clearance kinetics of virions from blood circulation. From these observations, it is commonly hypothesized that GAG-binding virions are rapidly removed from circulation due to ubiquitous expression of GAGs by vascular endothelial cells, thereby limiting viremia. Using an in vivo model for viremia, we compared the vascular clearance of low and enhanced GAG-binding viral variants of chikungunya (CHIKV), eastern-(EEEV), and Venezuelan-(VEEV) equine encephalitis viruses. We find GAG-binding virions are more quickly removed from circulation than their non-GAG-binding variant; however individual clearance kinetics vary between GAG-binding viruses, from swift (VEEV) to slow removal from circulation (EEEV). Remarkably, we find phagocytes are required for efficient vascular clearance of some enhanced GAG-binding virions. Moreover, transient depletion of vascular heparan sulfate (HS) impedes vascular clearance of only some GAG-binding viral variants and in a phagocyte-dependent manner, implying phagocytes can mediate vascular GAG-virion interactions. Finally, in direct contrast to mice, we find enhanced GAG-binding EEEV is resistant to vascular clearance in avian hosts, suggesting the existence of species-specificity in virion-GAG interactions. In summary, these data support a role for GAG-mediated clearance of some viral particles from the blood circulation, illuminate the potential of blood-contacting phagocytes as a site for GAG-virion binding, and suggest a role for species-specific GAG structures in arbovirus ecology.

Significance Statement

Previously, evidence of arbovirus-GAG interactions in vivo has been limited to associations between viral residues shown to promote enhanced GAG-binding phenotypes in vitro and in vivo phenotypes of viral dissemination and pathogenesis. By directly manipulating host GAG expression, we identified virion-GAG interactions in vivo and discovered a role for phagocyte-expressed GAGs in viral vascular clearance. Moreover, we observe species-specific differences in viral vascular clearance of enhanced GAG-binding virions between murine and avian hosts. These data suggest species-specific variation in GAG structure is a mechanism to distinguish amplifying from dead-end hosts for arbovirus transmission.

A molecular understanding of alphavirus entry and antibody protection

Alphaviruses are arthropod-transmitted RNA viruses that cause epidemics of human infection and disease on a global scale. These viruses are classified as either arthritogenic or encephalitic based on their genetic relatedness and the clinical syndromes they cause. Although there are currently no approved therapeutics or vaccines against alphaviruses, passive transfer of monoclonal antibodies confers protection in animal models. This Review highlights recent advances in our understanding of the host factors required for alphavirus entry, the mechanisms of action by which protective antibodies inhibit different steps in the alphavirus infection cycle and candidate alphavirus vaccines currently under clinical evaluation that focus on humoral immunity. A comprehensive understanding of alphavirus entry and antibody-mediated protection may inform the development of new classes of countermeasures for these emerging viruses.

Vaccine development for zoonotic viral diseases caused by positive‑sense single‑stranded RNA viruses belonging to the Coronaviridae and Togaviridae families (Review)

Outbreaks of zoonotic viral diseases pose a severe threat to public health and economies worldwide, with this currently being more prominent than it previously was human history. These emergency zoonotic diseases that originated and transmitted from vertebrates to humans have been estimated to account for approximately one billion cases of illness and have caused millions of deaths worldwide annually. The recent emergence of severe acute respiratory syndrome coronavirus-2 (coronavirus disease 2019) is an excellent example of the unpredictable public health threat causing a pandemic. The present review summarizes the literature data regarding the main vaccine developments in human clinical phase I, II and III trials against the zoonotic positive-sense single-stranded RNA viruses belonging to the Coronavirus and Alphavirus genera, including severe acute respiratory syndrome, Middle east respiratory syndrome, Venezuelan equine encephalitis virus, Semliki Forest virus, Ross River virus, Chikungunya virus and O'nyong-nyong virus. That there are neither vaccines nor effective antiviral drugs available against most of these viruses is undeniable. Therefore, new explosive outbreaks of these zoonotic viruses may surely be expected. The present comprehensive review provides an update on the status of vaccine development in different clinical trials against these viruses, as well as an overview of the present results of these trials.

Resurgence of Interest in Eastern Equine Encephalitis Virus Vaccine Development

Eastern equine encephalitis virus (EEEV; Family Togaviridae), is an endemic pathogen first isolated in 1933 with distribution primarily in the eastern US and Canada. The virus has caused periodic outbreaks in both humans and equines along the eastern seaboard and through the southern coastal states. While the outbreaks caused by EEEV have been sporadic and varied geographically since the discovery of the virus, it has continued to expand its range moving into the Midwest states as well. Additionally, one of the largest outbreaks was recorded in 2019 prompting concerns that outbreaks were becoming larger and more frequent. Because the virus can cause serious disease and because it is transmissible by both mosquitoes and aerosol, there has been renewed interest in identifying potential options for vaccines. Currently, there are no licensed vaccines and control relies completely on the use of personal protective measures and integrated vector control which have limited effectiveness for the EEEV vectors. Several vaccine candidates are currently being developed; this review will describe the multiple options under consideration for future development and assess their relative advantages and disadvantages.

Genetically modified attenuated salmonid alphavirus: A potential strategy for immunization of Atlantic salmon

Pancreas disease (PD) is a serious challenge in European salmonid aquaculture caused by salmonid alphavirus (SAV). In this study, we report the effect of immunization of Atlantic salmon with three attenuated infectious SAV3 strains with targeted mutations in a glycosylation site of the envelope E2 protein and/or in a nuclear localization signal in the capsid protein. In a pilot experiment, it was shown that the mutated viral strains replicated in fish, transmitted to naïve cohabitants and that the transmission had not altered the sequences. In the main experiment, the fish were immunized with the strains and challenged with SAV3 eight weeks after immunization. Immunization resulted in infection both in injected fish and 2 weeks later in the cohabitant fish, followed by a persistent but declining load of the mutated virus variants in the hearts. The immunized fish developed clinical signs and pathology consistent with PD prior to challenge. However, fish injected with the virus mutated in both E2 and capsid showed little clinical signs and had higher average weight gain than the groups immunized with the single mutated variants. The SAV strain used for challenge was not detected in the immunized fish indicating that these fish were protected against superinfection with SAV during the 12 weeks of the experiment.

Insights into Antibody-Mediated Alphavirus Immunity and Vaccine Development Landscape

Alphaviruses are mosquito-borne pathogens distributed worldwide in tropical and temperate areas causing a wide range of symptoms ranging from inflammatory arthritis-like manifestations to the induction of encephalitis in humans. Historically, large outbreaks in susceptible populations have been recorded followed by the development of protective long-lasting antibody responses suggesting a potential advantageous role for a vaccine. Although the current understanding of alphavirus antibody-mediated immunity has been mainly gathered in natural and experimental settings of chikungunya virus (CHIKV) infection, little is known about the humoral responses triggered by other emerging alphaviruses. This knowledge is needed to improve serology-based diagnostic tests and the development of highly effective cross-protective vaccines. Here, we review the role of antibody-mediated immunity upon arthritogenic and neurotropic alphavirus infections, and the current research efforts for the development of vaccines as a tool to control future alphavirus outbreaks.

Safety and immunogenicity of an inactivated eastern equine encephalitis virus vaccine

BACKGROUND

Eastern equine encephalitis virus (EEEV) is a mosquito borne alphavirus spread primarily in Atlantic and Gulf Coast regions of the United States. EEEV is the causative agent of a devastating meningoencephalitis syndrome, with approximately 30% mortality and significant morbidity. There is no licensed human vaccine against EEEV. An inactivated EEEV vaccine has been offered under investigational new drug (IND) protocols at the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) since 1976.

METHODS

Healthy at-risk laboratory personnel received inactivated PE-6 strain EEEV (TSI-GSD 104) vaccine under two separate IND protocols. Protocol FY 99-11 (2002-2008) had a primary series consisting of doses on day 0, 7, and 28. Protocol FY 06-31 (2008-2016) utilized a primary series with doses on day 0 and 28, and month 6. Participants with an inadequate immune response, plaque reduction neutralization test with 80% cut-off (PRNT80) titer < 40, received booster vaccination. Volunteers with prior EEEV vaccination were eligible to enroll for booster doses based on annual titer evaluation.

RESULTS

The FY06-31 dosing schema resulted in significantly greater post-primary series immune response (PRNT80 ≥ 40) rates (84% vs 54%) and geometric mean titers (184.1 vs 39.4). The FY 06-31 dosing schema also resulted in significantly greater cumulative annual immune response rates from 1 to up to 7 years post vaccination (75% vs 59%) and geometric mean of titers (60.1 vs 43.0). The majority of probably or definitely related adverse events were mild and local; there were no probably or definitely related serious adverse events.

CONCLUSIONS

Inactivated PE-6 EEEV vaccine is safe and immunogenic in at-risk laboratory personnel. A prolonged primary series, with month 6 dose, significantly improved vaccine immunogenicity both post-primary series and longitudinally on annual titers. Despite decades of safe use under IND, full licensure is not planned due to manufacturing constraints, and ongoing development of alternatives.

A Productive Expression Platform Derived from Host-Restricted Eilat Virus: Its Extensive Validation and Novel Strategy

Most alphaviruses are transmitted by mosquitoes and infect a wide range of insects and vertebrates. However, Eilat virus (EILV) is defective for infecting vertebrate cells at multiple levels of the viral life cycle. This host-restriction property renders EILV an attractive expression platform since it is not infectious for vertebrates and therefore provides a highly advantageous safety profile. Here, we investigated the feasibility of versatile EILV-based expression vectors. By replacing the structural genes of EILV with those of other alphaviruses, we generated seven different chimeras. These chimeras were readily rescued in the original mosquito cells and were able to reach high titers, suggesting that EILV is capable of packaging the structural proteins of different lineages. We also explored the ability of EILV to express authentic antigens via double subgenomic (SG) RNA vectors. Four foreign genetic materials of varied length were introduced into the EILV genome, and the expressed heterologous genetic materials were readily detected in the infected cells. By inserting an additional SG promoter into the chimera genome containing the structural genes of Chikungunya virus (CHIKV), we developed a bivalent vaccine candidate against CHIKV and Zika virus. These data demonstrate the outstanding compatibility of the EILV genome. The produced recombinants can be applied to vaccine and diagnostic tool development, but more investigations are required.

Eastern Equine Encephalitis Virus Seroprevalence in Maine Cervids, 2012-2017

Eastern equine encephalitis virus (EEEV) first emerged in Maine in the early 2000s and resulted in an epizootic outbreak in 2009. Since 2009, serum samples from cervids throughout Maine have been collected and assessed for the presence of neutralizing antibodies to EEEV to assess EEEV activity throughout the state. We tested 1,119 Odocoileus virginianus (white-tailed deer) and 982 Alces americanus (moose) serum samples collected at tagging stations during the hunting seasons from 2012 to 2017 throughout the state of Maine. Odocoileus virginianus from all 16 counties were EEEV seropositive, whereas A. americanus were seropositive in the northwestern counties of Aroostook, Somerset, Piscataquis, and Franklin counties. Seroprevalence in O. virginianus ranged from 6.6% to 21.2% and in A. americanus from 6.6% to 10.1%. Data from this report in conjunction with findings previously reported from 2009 to 2011 indicate that EEEV is endemic throughout Maine.

Hypervariable Domain of nsP3 of Eastern Equine Encephalitis Virus Is a Critical Determinant of Viral Virulence

Eastern equine encephalitis virus (EEEV) is the most pathogenic member of the Alphavirus genus in the Togaviridae family. This virus continues to circulate in the New World and has a potential for deliberate use as a bioweapon. Despite the public health threat, to date no attenuated EEEV variants have been applied as live EEEV vaccines. Our previous studies demonstrated the critical function of the hypervariable domain (HVD) in EEEV nsP3 for the assembly of viral replication complexes (vRCs). EEEV HVD contains short linear motifs that recruit host proteins required for vRC formation and function. In this study, we developed a set of EEEV mutants that contained combinations of deletions in nsP3 HVD and clustered mutations in capsid protein, and tested the effects of these modifications on EEEV infection in vivo These mutations had cumulative negative effects on viral ability to induce meningoencephalitis. The deletions of two critical motifs, which interact with the members of cellular FXR and G3BP protein families, made EEEV cease to be neurovirulent. The additional clustered mutations in capsid protein, which affect its ability to induce transcriptional shutoff, diminished EEEV's ability to develop viremia. Most notably, despite the inability to induce detectable disease, the designed EEEV mutants remained highly immunogenic and, after a single dose, protected mice against subsequent infection with wild-type (wt) EEEV. Thus, alterations of interactions of EEEV HVD and likely HVDs of other alphaviruses with host factors represent an important direction for development of highly attenuated viruses that can be applied as live vaccines.IMPORTANCE Hypervariable domains (HVDs) of alphavirus nsP3 proteins recruit host proteins into viral replication complexes. The sets of HVD-binding host factors are specific for each alphavirus, and we have previously identified those specific for EEEV. The results of this study demonstrate that the deletions of the binding sites of the G3BP and FXR protein families in the nsP3 HVD of EEEV make the virus avirulent for mice. Mutations in the nuclear localization signal in EEEV capsid protein have an additional negative effect on viral replication in vivo Despite the inability to cause a detectable disease, the double HVD and triple HVD/capsid mutants induce high levels of neutralizing antibodies. Single immunization protects mice against infection with the highly pathogenic North American strain of EEEV. High safety, the inability to revert to wild-type phenotype, and high immunogenicity make the designed mutants attractive vaccine candidates for EEEV infection.

Vaccine Advances against Venezuelan, Eastern, and Western Equine Encephalitis Viruses

Vaccinations are a crucial intervention in combating infectious diseases. The three neurotropic Alphaviruses, Eastern (EEEV), Venezuelan (VEEV), and Western (WEEV) equine encephalitis viruses, are pathogens of interest for animal health, public health, and biological defense. In both equines and humans, these viruses can cause febrile illness that may progress to encephalitis. Currently, there are no licensed treatments or vaccines available for these viruses in humans. Experimental vaccines have shown variable efficacy and may cause severe adverse effects. Here, we outline recent strategies used to generate vaccines against EEEV, VEEV, and WEEV with an emphasis on virus-vectored and plasmid DNA delivery. Despite candidate vaccines protecting against one of the three viruses, few studies have demonstrated an effective trivalent vaccine. We evaluated the potential of published vaccines to generate cross-reactive protective responses by comparing DNA vaccine sequences to a set of EEEV, VEEV, and WEEV genomes and determining the vaccine coverages of potential epitopes. Finally, we discuss future directions in the development of vaccines to combat EEEV, VEEV, and WEEV.

Novel Insect-Specific Eilat Virus-Based Chimeric Vaccine Candidates Provide Durable, Mono- and Multivalent, Single-Dose Protection against Lethal Alphavirus Challenge

Most alphaviruses are mosquito borne and exhibit a broad host range, infecting many different vertebrates, including birds, rodents, equids, humans, and nonhuman primates. Recently, a host-restricted, mosquito-borne alphavirus, Eilat virus (EILV), was described with an inability to infect vertebrate cells based on defective attachment and/or entry, as well as a lack of genomic RNA replication. We investigated the utilization of EILV recombinant technology as a vaccine platform against eastern (EEEV) and Venezuelan equine encephalitis viruses (VEEV), two important pathogens of humans and domesticated animals. EILV chimeras containing structural proteins of EEEV or VEEV were engineered and successfully rescued in Aedes albopictus cells. Cryo-electron microscopy reconstructions at 8 and 11 Å of EILV/VEEV and EILV/EEEV, respectively, showed virion and glycoprotein spike structures similar to those of VEEV-TC83 and other alphaviruses. The chimeras were unable to replicate in vertebrate cell lines or in brains of newborn mice when injected intracranially. Histopathologic examinations of the brain tissues showed no evidence of pathological lesions and were indistinguishable from those of mock-infected animals. A single-dose immunization of either monovalent or multivalent EILV chimera(s) generated neutralizing antibody responses and protected animals against lethal challenge 70 days later. Lastly, a single dose of monovalent EILV chimeras generated protective responses as early as day 1 postvaccination and partial or complete protection by day 6. These data demonstrate the safety, immunogenicity, and efficacy of novel insect-specific EILV-based chimeras as potential EEEV and VEEV vaccines.IMPORTANCE Mostly in the last decade, insect-specific viruses have been discovered in several arbovirus families. However, most of these viruses are not well studied and largely have been ignored. We explored the use of the mosquito-specific alphavirus EILV as an alphavirus vaccine platform in well-established disease models for eastern (EEE) and Venezuelan equine encephalitis (VEE). EILV-based chimeras replicated to high titers in a mosquito cell line yet retained their host range restriction in vertebrates both in vitro and in vivo In addition, the chimeras generated immune responses that were higher than those of other human and/or equine vaccines. These findings indicate the feasibility of producing a safe, efficacious, mono- or multivalent vaccine against the encephalitic alphaviruses VEEV and EEEV. Lastly, these data demonstrate how host-restricted, insect-specific viruses can be engineered to develop vaccines against related pathogenic arboviruses that cause severe disease in humans and domesticated animals.

Chikungunya Virus Vaccines: Viral Vector-Based Approaches

In 2013, a major chikungunya virus (CHIKV) epidemic reached the Americas. In the past 2 years, >1.7 million people have been infected. In light of the current epidemic, with millions of people in North and South America at risk, efforts to rapidly develop effective vaccines have increased. Here, we focus on CHIKV vaccines that use viral-vector technologies. This group of vaccine candidates shares an ability to potently induce humoral and cellular immune responses by use of highly attenuated and safe vaccine backbones. So far, well-described vectors such as modified vaccinia virus Ankara, complex adenovirus, vesicular stomatitis virus, alphavirus-based chimeras, and measles vaccine Schwarz strain (MV/Schw) have been described as potential vaccines. We summarize here the recent data on these experimental vaccines, with a focus on the preclinical and clinical activities on the MV/Schw-based candidate, which is the first CHIKV-vectored vaccine that has completed a clinical trial.

Seasonal Patterns in Eastern Equine Encephalitis Virus Antibody in Songbirds in Southern Maine

The intent of this study was to assess passerine eastern equine encephalitis virus (EEEv) seroprevalence during the breeding season in southern Maine by testing songbird species identified in the literature as amplifying hosts of this virus. In 2013 and 2014, we collected serum samples from songbirds at a mainland site and an offshore island migratory stopover site, and screened samples for EEEv antibodies using plaque reduction neutralization tests. We compared seasonal changes in EEEv antibody seroprevalence in young (hatched in year of capture) and adult birds at the mainland site, and also compared early season seroprevalence in mainland versus offshore adult birds. EEEv seroprevalence did not differ significantly between years at either site. During the early season (May), EEEv antibody seroprevalence was substantially lower (9.6%) in the island migrant adults than in mainland adults (42.9%), 2013-2014. On the mainland, EEEv antibody seroprevalence in young birds increased from 12.9% in midseason (June-August) to 45.6% in late season (September/October), 2013-2014. Seroprevalence in adult birds did not differ between seasons (48.8% vs. 53.3%). EEEv activity in Maine has increased in the past decade as measured by increased virus detection in mosquitoes and veterinary cases. High EEEv seroprevalence in young birds-as compared to that of young birds in other studies-corresponded with two consecutive active EEEv years in Maine. We suggest that young, locally hatched songbirds be sampled as a part of long-term EEEv surveillance, and provide a list of suggested species to sample, including EEEv "superspreaders."

Epidemiology of Emergent Madariaga Encephalitis in a Region with Endemic Venezuelan Equine Encephalitis: Initial Host Studies and Human Cross-Sectional Study in Darien, Panama

Background

Neurotropic arboviral infections are an important cause of encephalitis. A zoonotic, vector-borne alphavirus, Madariaga virus (MADV; formerly known as South American eastern equine encephalitis virus), caused its first documented human outbreak in 2010 in Darien, Panama, where the genetically similar Venezuelan equine encephalitis virus (VEEV) is endemic. We report the results of a seroprevalence survey of animals and humans, illustrating contrasting features of MADV and VEEV ecology and epidemiology.

Methods

Small mammals were trapped in 42 sites in Darien, Panama, using Sherman traps, Tomahawk traps, and mist nets for bats. Blood was tested for the presence of neutralizing antibodies to MADV and VEEV. In addition, bird sera collected in 2007 in Chagres, Panama, were tested for MADV and VEEV neutralizing antibodies. Viremia was ascertained by RT-PCR. Human exposure to these two viruses was determined by IgG ELISA, followed by plaque reduction neutralization tests. To identify relevant risk factors for MADV or VEEV exposure, logistic regression analysis was performed, and the most parsimonious model was selected based on the Akaike information criterion.

Results

The animal survey yielded 32 bats (16 species), 556 rodents (12 species), and 20 opossums (4 species). The short-tailed cane mouse (Zygodontomys brevicauda) found abundantly in pasture and farms, had the highest MADV seroprevalence (8.3%). For VEEV, the shrub and forest-dwelling long-whiskered rice rat (Transandinomys bolivaris) had the highest seroprevalence (19.0%). Viremia was detected in one animal (Z. brevicauda). Of the 159 bird sera (50 species) tested, none were positive for either virus. In humans (n = 770), neutralizing antibodies to MADV and VEEV were present in 4.8% and 31.5%, respectively. MADV seropositivity was positively associated with cattle ranching, farming, and fishing. Having VEEV antibodies and shrubs near the house diminished risk. Age, forest work, farming and fishing were risk factors for VEEV, while having MADV antibodies, glazed windows, waste pick-up and piped water were protective.

Conclusion

Our findings suggest that the short-tailed cane mouse and the long-whiskered rice rat serve as hosts for MADV and VEEV, respectively. The preferred habitat of these rodent species coincides with areas associated with human infection risk. Our findings also indicate that MADV emerged recently in humans, and that the transmission cycles of these two sympatric alphaviruses differ spatially and in host utilization.

Arthropod-borne viruses are important causes of encephalitis. In 2010, the first documented human outbreak of the mosquito-borne, zoonotic Madariaga virus (MADV) occurred in the Darien region of Panama. Neither its epidemiology nor its transmission cycle is understood. In this study, the authors searched for possible animal hosts of this virus, and sought to describe its epidemiology. They contrast the findings with those for Venezuelan equine encephalitis virus (VEEV), an endemic, genetically similar virus. Zygodontomys brevicauda, the short-tailed cane mouse, had the highest seroprevalence for MADV. This rodent species is most often found in pasture and farm land. Indeed, the risk factors for human MADV exposure were cattle ranching and farming. The animal with highest seroprevalence for VEEV, the long-whiskered rice rat (Transandinomys bolivaris), commonly occurs in forest, and the epidemiological risk factors included working in the forest. Farming and fishing were risk factors for exposure to both viruses, and having antibodies to one virus diminished the risk of being positive for the other. Increasing prevalence with age was seen for VEEV, confirming that VEEV is endemic in the region. This association was absent for MADV, suggesting that this virus emerged recently to infect humans.

Prevalence of eastern equine encephalitis virus antibodies among white-tailed deer populations in Maine

During the fall of 2010, 332 deer serum samples were collected from 15 of the 16 (93.8%) Maine counties and screened for eastern equine encephalitis virus (EEEV) antibodies using plaque reduction neutralizing tests (PRNTs). The aim was to detect and map EEEV activity in the state of Maine. Forty-seven of the 332 (14.2%) sera were positive for EEEV antibodies, showing a much wider distribution of EEEV activity in Maine than previously known. The percentage of EEEV antibody-positive deer sera was ≥10% in six counties-Piscataquis (100%), Somerset (28.6%), Waldo (22.2%), Penobscot (21.7%), Kennebec (13.7%), and Sagadahoc (10%). Positive sera were detected in all the six counties (Somerset, Waldo, Penobscot, Kennebec, Cumberland, and York) that were positive in 2009, suggesting endemic EEEV activity in these counties. EEEV antibodies were not detected in sera collected in five counties-Franklin, Knox, Lincoln, Oxford, and Washington-which was either due to low sample size or lack of EEEV activity in these counties. Our data suggest higher EEEV activity in central Maine compared to southern Maine, whereas EEEV activity in Maine has historically been associated with the southern counties of York and Cumberland.

Production of a Sindbis/Eastern Equine Encephalitis chimeric virus inactivated cell culture antigen

Eastern Equine Encephalitis virus (EEEV) is a medically important pathogen that can cause severe encephalitis in humans, with mortality rates ranging from 30 to 80%. Unfortunately there are no antivirals or licensed vaccines available for human use, and laboratory diagnosis is essential to differentiate EEEV infection from other pathogens with similar clinical manifestations. The Arboviral Diseases Branch (ADB) reference laboratory at the CDC Division of Vector-Borne Diseases (DVBD) produces reference antigens used in serological assays such as the EEEV immunoglobulin M antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA). However, EEEV is classified as a HHS select agent and requires biosafety level (BSL) three containment, limiting EEEV antigen production in non-select agent and BSL-2 laboratories. A recombinant Sindbis virus (SINV)/EEEV has been constructed for use under BSL-2 conditions and is not regulated as a select agent. Cell culture production of inactivated EEEV antigen from SINV/EEEV for use in the EEEV MAC-ELISA is reported here. Cell culture conditions and inactivation procedures were analyzed for SINV/EEEV using a recently developed antigen production algorithm, with the MAC-ELISA as the performance indicator.

RNA-based viral vectors

The advent of reverse genetic approaches to manipulate the genomes of both positive (+) and negative (-) sense RNA viruses allowed researchers to harness these genomes for basic research. Manipulation of positive sense RNA virus genomes occurred first largely because infectious RNA could be transcribed directly from cDNA versions of the RNA genomes. Manipulation of negative strand RNA virus genomes rapidly followed as more sophisticated approaches to provide RNA-dependent RNA polymerase complexes coupled with negative-strand RNA templates were developed. These advances have driven an explosion of RNA virus vaccine vector development. That is, development of approaches to exploit the basic replication and expression strategies of RNA viruses to produce vaccine antigens that have been engineered into their genomes. This study has led to significant preclinical testing of many RNA virus vectors against a wide range of pathogens as well as cancer targets. Multiple RNA virus vectors have advanced through preclinical testing to human clinical evaluation. This review will focus on RNA virus vectors designed to express heterologous genes that are packaged into viral particles and have progressed to clinical testing.

Mouse models of alphavirus-induced inflammatory disease

Part of the Togaviridae family, alphaviruses are arthropod-borne viruses that are widely distributed throughout the globe. Alphaviruses are able to infect a variety of vertebrate hosts, but in humans, infection can result in extensive morbidity and mortality. Symptomatic infection can manifest as fever, an erythematous rash and/or significant inflammatory pathologies such as arthritis and encephalitis. Recent overwhelming outbreaks of alphaviral disease have highlighted the void in our understanding of alphavirus pathogenesis and the re-emergence of alphaviruses has given new impetus to anti-alphaviral drug design. In this review, the development of viable mouse models of Old Word and New World alphaviruses is examined. How mouse models that best replicate human disease have been used to elucidate the immunopathology of alphavirus pathogenesis and trial novel therapeutic discoveries is also discussed.

Venezuelan equine encephalitis virus variants lacking transcription inhibitory functions demonstrate highly attenuated phenotype

Alphaviruses represent a significant public health threat worldwide. They are transmitted by mosquitoes and cause a variety of human diseases ranging from severe meningoencephalitis to polyarthritis. To date, no efficient and safe vaccines have been developed against any alphavirus infection. However, in recent years, significant progress has been made in understanding the mechanism of alphavirus replication and virus-host interactions. These data have provided the possibility for the development of new rationally designed alphavirus vaccine candidates that combine efficient immunogenicity, high safety, and inability to revert to pathogenic phenotype. New attenuated variants of Venezuelan equine encephalitis virus (VEEV) designed in this study combine a variety of characteristics that independently contribute to a reduction in virulence. These constructs encode a noncytopathic VEEV capsid protein that is incapable of interfering with the innate immune response. The capsid-specific mutations strongly affect neurovirulence of the virus. In other constructs, they were combined with changes in control of capsid translation and an extensively mutated packaging signal. These modifications also affected the residual neurovirulence of the virus, but it remained immunogenic, and a single immunization protected mice against subsequent infection with epizootic VEEV. Similar approaches of attenuation can be applied to other encephalitogenic New World alphaviruses.

IMPORTANCE

Venezuelan equine encephalitis virus (VEEV) is an important human and animal pathogen, which causes periodic outbreaks of highly debilitating disease. Despite a continuous public health threat, no safe and efficient vaccine candidates have been developed to date. In this study, we applied accumulated knowledge about the mechanism of VEEV replication, RNA packaging, and interaction with the host to design new VEEV vaccine candidates that demonstrate exceptionally high levels of safety due to a combination of extensive modifications in the viral genome. The introduced mutations did not affect RNA replication or structural protein synthesis but had deleterious effects on VEEV neuroinvasion and virulence. In spite of dramatically reduced virulence, the designed mutants remained highly immunogenic and protected mice against subsequent infection with epizootic VEEV. Similar methodologies can be applied for attenuation of other encephalitogenic New World alphaviruses.

Combined alphavirus replicon particle vaccine induces durable and cross-protective immune responses against equine encephalitis viruses

Alphavirus replicons were evaluated as potential vaccine candidates for Venezuelan equine encephalitis virus (VEEV), western equine encephalitis virus (WEEV), or eastern equine encephalitis virus (EEEV) when given individually or in combination (V/W/E) to mice or cynomolgus macaques. Individual replicon vaccines or the combination V/W/E replicon vaccine elicited strong neutralizing antibodies in mice to their respective alphavirus. Protection from either subcutaneous or aerosol challenge with VEEV, WEEV, or EEEV was demonstrated out to 12 months after vaccination in mice. Individual replicon vaccines or the combination V/W/E replicon vaccine elicited strong neutralizing antibodies in macaques and demonstrated good protection against aerosol challenge with an epizootic VEEV-IAB virus, Trinidad donkey. Similarly, the EEEV replicon and V/W/E combination vaccine elicited neutralizing antibodies against EEEV and protected against aerosol exposure to a North American variety of EEEV. Both the WEEV replicon and combination V/W/E vaccination, however, elicited poor neutralizing antibodies to WEEV in macaques, and the protection conferred was not as strong. These results demonstrate that a combination V/W/E vaccine is possible for protection against aerosol challenge and that cross-interference between the vaccines is minimal. Importance: Three related viruses belonging to the genus Alphavirus cause severe encephalitis in humans: Venezuelan equine encephalitis virus (VEEV), western equine encephalitis virus (WEEV), and eastern equine encephalitis virus (EEEV). Normally transmitted by mosquitoes, these viruses can cause disease when inhaled, so there is concern that these viruses could be used as biological weapons. Prior reports have suggested that vaccines for these three viruses might interfere with one another. We have developed a combined vaccine for Venezuelan equine encephalitis, western equine encephalitis, and eastern equine encephalitis expressing the surface proteins of all three viruses. In this report we demonstrate in both mice and macaques that this combined vaccine is safe, generates a strong immune response, and protects against aerosol challenge with the viruses that cause Venezuelan equine encephalitis, western equine encephalitis, and eastern equine encephalitis.

Second generation inactivated eastern equine encephalitis virus vaccine candidates protect mice against a lethal aerosol challenge

Currently, there are no FDA-licensed vaccines or therapeutics for eastern equine encephalitis virus (EEEV) for human use. We recently developed several methods to inactivate CVEV1219, a chimeric live-attenuated eastern equine encephalitis virus (EEEV). Dosage and schedule studies were conducted to evaluate the immunogenicity and protective efficacy of three potential second-generation inactivated EEEV (iEEEV) vaccine candidates in mice: formalin-inactivated CVEV1219 (fCVEV1219), INA-inactivated CVEV1219 (iCVEV1219) and gamma-irradiated CVEV1219 (gCVEV1219). Both fCVEV1219 and gCVEV1219 provided partial to complete protection against an aerosol challenge when administered by different routes and schedules at various doses, while iCVEV1219 was unable to provide substantial protection against an aerosol challenge by any route, dose, or schedule tested. When evaluating antibody responses, neutralizing antibody, not virus specific IgG or IgA, was the best correlate of protection. The results of these studies suggest that both fCVEV1219 and gCVEV1219 should be evaluated further and considered for advancement as potential second-generation inactivated vaccine candidates for EEEV.

CpG/Poly (I:C) mixed adjuvant priming enhances the immunogenicity of a DNA vaccine against eastern equine encephalitis virus in mice

Eastern equine encephalitis virus (EEEV) poses a serious public health threat in many countries. Therefore, developing efficient vaccine against EEEV remains an important challenge in the field of disease control. To identify immunogenic proteins in EEEV, we constructed an expression vector containing the protein coding genes C, E3, E2, 6k, and E1 (pcDNA3.1-C-E). After verifying the target gene expression in 293 T cells, we immunized BALB/c mice with the pcDNA3.1-C-E vector as a DNA vaccine in conjunction with either CpG or poly (I:C) or a mixture of both adjuvants and monitored various aspects of the immune response. After two immunizations, the mice vaccinated with antigen plus mixed CpG/poly (I:C) adjuvant exhibited significantly stronger IFN-gamma responses and generated high-level CD4(+) cell responses for the cytokines IL-2, IL-4, and IFN-γ and CD8(+) T cell responses for the cytokines IL-2 and IFN-γ compared to the mice vaccinated with the corresponding antigen plus CpG or poly(I:C) alone. In addition, the higher antibody titers against EEEV effectively neutralized the EEEV pseudoviruses in the group immunized with antigen plus mixed CpG/poly (I:C) adjuvant after tertiary immunization. This study demonstrates that the pcDNA3.1-C-E plasmids in conjunction with mixed CpG/poly (I:C) adjuvant priming maximize the cellular immune response and specific antibody generation in mice. Moreover, this mixed adjuvant priming provides a promising strategy for enhancing the immune effectiveness of a DNA vaccine against EEEV.

Liposome-antigen-nucleic acid complexes protect mice from lethal challenge with western and eastern equine encephalitis viruses

Alphaviruses are mosquito-borne viruses that cause significant disease in animals and humans. Western equine encephalitis virus (WEEV) and eastern equine encephalitis virus (EEEV), two New World alphaviruses, can cause fatal encephalitis, and EEEV is a select agent of concern in biodefense. However, we have no antiviral therapies against alphaviral disease, and current vaccine strategies target only a single alphavirus species. In an effort to develop new tools for a broader response to outbreaks, we designed and tested a novel alphavirus vaccine comprised of cationic lipid nucleic acid complexes (CLNCs) and the ectodomain of WEEV E1 protein (E1ecto). Interestingly, we found that the CLNC component, alone, had therapeutic efficacy, as it increased survival of CD-1 mice following lethal WEEV infection. Immunization with the CLNC-WEEV E1ecto mixture (lipid-antigen-nucleic acid complexes [LANACs]) using a prime-boost regimen provided 100% protection in mice challenged with WEEV subcutaneously, intranasally, or via mosquito. Mice immunized with LANACs mounted a strong humoral immune response but did not produce neutralizing antibodies. Passive transfer of serum from LANAC E1ecto-immunized mice to nonimmune CD-1 mice conferred protection against WEEV challenge, indicating that antibody is sufficient for protection. In addition, the LANAC E1ecto immunization protocol significantly increased survival of mice following intranasal or subcutaneous challenge with EEEV. In summary, our LANAC formulation has therapeutic potential and is an effective vaccine strategy that offers protection against two distinct species of alphavirus irrespective of the route of infection. We discuss plausible mechanisms as well the potential utility of our LANAC formulation as a pan-alphavirus vaccine.

Vaccines and therapeutics for the encephalitic alphaviruses

This article is a review of vaccines and therapeutics in development for the encephalitic alphaviruses, which includes eastern equine encephalitis virus, western equine encephalitis virus and Venezuelan equine encephalitis virus. The encephalitic alphaviruses are endemic within regions in North and South America. Hosts are normally exposed after being bitten by infectious mosquitoes, and infection can develop into encephalitis in equines and humans with severe rates of morbidity and mortality. These viruses are also potential biological threat agents, being highly infectious via an aerosol route of exposure. In humans, equine encephalitis virus and western equine encephalitis virus are neurotropic viruses targeting the CNS and causing encephalitis. Mortality rates are 50 and 10%, respectively, for these viruses. On the other hand, Venezuelan equine encephalitis virus produces a systemic influenza-like illness with pathogenesis in the lungs and lymphoid tissue in adults and older children. The incidence of encephalitis is less than 5% in younger children with a case–mortality rate of 1%. The host response to virus infectivity is briefly discussed, along with a number of promising therapeutic and prophylactic approaches. These approaches can be broadly classified as: virus-specific, including vaccines, antibody therapy and gene-silencing oligonucleotides; or broad-spectrum, including interferon and activation of the host‘s innate immunity.

A chimeric Sindbis-based vaccine protects cynomolgus macaques against a lethal aerosol challenge of eastern equine encephalitis virus

Eastern equine encephalitis virus (EEEV) is a mosquito-borne alphavirus that causes sporadic, often fatal disease outbreaks in humans and equids, and is also a biological threat agent. Two chimeric vaccine candidates were constructed using a cDNA clone with a Sindbis virus (SINV) backbone and structural protein genes from either a North (SIN/NAEEEV) or South American (SIN/SAEEEV) strain of EEEV. The vaccine candidates were tested in a nonhuman primate (NHP) model of eastern equine encephalitis (EEE). Cynomolgus macaques were either sham-vaccinated, or vaccinated with a single dose of either SIN/NAEEEV or SIN/SAEEEV. After vaccination, animals were challenged by aerosol with a virulent North American strain of EEEV (NA EEEV). The SIN/NAEEEV vaccine provided significant protection, and most vaccinated animals survived EEEV challenge (82%) with little evidence of disease, whereas most SIN/SAEEEV-vaccinated (83%) and control (100%) animals died. Protected animals exhibited minimal changes in temperature and cardiovascular rhythm, whereas unprotected animals showed profound hyperthermia and changes in heart rate postexposure. Acute inflammation and neuronal necrosis were consistent with EEEV-induced encephalitis in unprotected animals, whereas no encephalitis-related histopathologic changes were observed in the SIN/NAEEEV-vaccinated animals. These results demonstrate that the chimeric SIN/NAEEEV vaccine candidate protects against an aerosol EEEV exposure.

Serological evidence for eastern equine encephalitis virus activity in white-tailed deer, Odocoileus virginianus, in Vermont, 2010

Serum samples from 489 free-ranging white-tailed deer (Odocoileus virginianus) were screened for antibodies against the Eastern equine encephalitis virus (EEEV) using plaque reduction neutralization tests (PRNTs). EEEV antibodies were detected in 10.2% of serum samples. This is the first evidence that EEEV is present in Vermont. Serum was collected from deer in all 14 counties in the state, and positive EEEV sera were found in 12 (85%) of 14 counties, suggesting statewide EEEV activity in Vermont. Analysis of the spatial distribution of PRNT-positive samples revealed a random distribution of EEEV throughout the state. The results indicate widespread EEEV activity in Vermont and suggest that EEEV is not a recent introduction to the state but that EEEV activity has not been detected until now.

Eastern equine encephalitis in moose (Alces americanus) in northeastern Vermont

During fall 2010, 21 moose (Alces americanus) sera collected in northeastern Vermont were screened for eastern equine encephalitis virus (EEEV) antibodies using plaque reduction neutralization tests. Six (29%) were antibody positive. This is the first evidence of EEEV activity in Vermont, and the second report of EEEV antibodies in moose.

Pseudoinfectious Venezuelan equine encephalitis virus: a new means of alphavirus attenuation

Venezuelan equine encephalitis virus (VEEV) is a reemerging virus that causes a severe and often fatal disease in equids and humans. In spite of a continuous public health threat, to date, no vaccines or antiviral drugs have been developed for human use. Experimental vaccines demonstrate either poor efficiency or severe adverse effects. In this study, we developed a new strategy of alphavirus modification aimed at making these viruses capable of replication and efficient induction of the immune response without causing a progressive infection, which might lead to disease development. To achieve this, we developed a pseudoinfectious virus (PIV) version of VEEV. VEE PIV mimics natural viral infection in that it efficiently replicates its genome, expresses all of the viral structural proteins, and releases viral particles at levels similar to those found in wild-type VEEV-infected cells. However, the mutations introduced into the capsid protein make this protein almost incapable of packaging the PIV genome, and most of the released virions lack genetic material and do not produce a spreading infection. Thus, VEE PIV mimics viral infection in terms of antigen production but is safer due to its inability to incorporate the viral genome into released virions. These genome-free virions are referred to as virus-like particles (VLPs). Importantly, the capsid-specific mutations introduced make the PIV a very strong inducer of the innate immune response and add self-adjuvant characteristics to the designed virus. This unique strategy of virus modification can be applied for vaccine development against other alphaviruses.

VIPR HMM: a hidden Markov model for detecting recombination with microbial detection microarrays

MOTIVATION

Current methods in diagnostic microbiology typically focus on the detection of a single genomic locus or protein in a candidate agent. The presence of the entire microbe is then inferred from this isolated result. Problematically, the presence of recombination in microbial genomes would go undetected unless other genomic loci or protein components were specifically assayed. Microarrays lend themselves well to the detection of multiple loci from a given microbe; furthermore, the inherent nature of microarrays facilitates highly parallel interrogation of multiple microbes. However, none of the existing methods for analyzing diagnostic microarray data has the capacity to specifically identify recombinant microbes. In previous work, we developed a novel algorithm, VIPR, for analyzing diagnostic microarray data.

RESULTS

We have expanded upon our previous implementation of VIPR by incorporating a hidden Markov model (HMM) to detect recombinant genomes. We trained our HMM on a set of non-recombinant parental viruses and applied our method to 11 recombinant alphaviruses and 4 recombinant flaviviruses hybridized to a diagnostic microarray in order to evaluate performance of the HMM. VIPR HMM correctly identified 95% of the 62 inter-species recombination breakpoints in the validation set and only two false-positive breakpoints were predicted. This study represents the first description and validation of an algorithm capable of detecting recombinant viruses based on diagnostic microarray hybridization patterns.

AVAILABILITY

VIPR HMM is freely available for academic use and can be downloaded from http://ibridgenetwork.org/wustl/vipr.

CONTACT

davewang@borcim.wustl.edu.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

New PARP gene with an anti-alphavirus function

Alphaviruses represent a highly important group of human and animal pathogens, which are transmitted by mosquito vectors between vertebrate hosts. The hallmark of alphavirus infection in vertebrates is the induction of a high-titer viremia, which is strongly dependent on the ability of the virus to interfere with host antiviral responses on both cellular and organismal levels. The identification of cellular factors, which are critical in orchestrating virus clearance without the development of cytopathic effect, may prove crucial in the design of new and highly effective antiviral treatments. To address this issue, we have developed a noncytopathic Venezuelan equine encephalitis virus (VEEV) mutant that can persistently replicate in cells defective in type I interferon (IFN) production or signaling but is cleared from IFN signaling-competent cells. Using this mutant, we analyzed (i) the spectrum of cellular genes activated by virus replication in the persistently infected cells and (ii) the spectrum of genes activated during noncytopathic virus clearance. By applying microarray-based technology and bioinformatic analysis, we identified a number of IFN-stimulated genes (ISGs) specifically activated during VEEV clearance. One of these gene products, the long isoform of PARP12 (PARP12L), demonstrated an inhibitory effect on the replication of VEEV, as well as other alphaviruses and several different types of other RNA viruses. Additionally, overexpression of two other members of the PARP gene superfamily was also shown to be capable of inhibiting VEEV replication.

Venezuelan equine encephalitis in a teenager visiting Central America

BACKGROUND

Stupor, coma, and other alterations of consciousness are among the most serious life-threatening emergencies faced by the emergency department physician. When a patient arrives with altered mentation from Central or South America, the usual causes that occur in the United States must be considered; however, other unusual tropical disease must be excluded, such as Venezuelan equine encephalitis (VEE).

OBJECTIVE

This study aimed to review the clinical features of VEE.

CASE

A 17-year-old female traveled to Belize and developed vomiting, diarrhea, fever, headaches, and myalgias. Over the next few hours, she became disoriented and had a generalized seizure. She was given diazepam, 50% dextrose, phenytoin, mannitol, and vitamin K. A computed tomographic scan of the head was unremarkable. Her parents arranged for a medical air transport. After eliminating other possibilities, she was diagnosed with VEE, which was confirmed in the laboratory. Over the next week, her mental status improved back to her normal neurologic baseline.

CONCLUSIONS

Venezuelan equine encephalitis is an acute viral disease that causes acute illness in equines and humans, with symptoms ranging from a mild, flu-like syndrome to encephalitis or death. Laboratory abnormalities are common and include elevated hepatic transaminases, lymphocytosis, eosinophilia, and thrombocytopenia. Treatment is supportive, and complete recovery is expected within several weeks in most patients.

Attenuation of Chikungunya virus vaccine strain 181/clone 25 is determined by two amino acid substitutions in the E2 envelope glycoprotein

Chikungunya virus (CHIKV) is the mosquito-borne alphavirus that is the etiologic agent of massive outbreaks of arthralgic febrile illness that recently affected millions of people in Africa and Asia. The only CHIKV vaccine that has been tested in humans, strain 181/clone 25, is a live-attenuated derivative of Southeast Asian human isolate strain AF15561. The vaccine was immunogenic in phase I and II clinical trials; however, it induced transient arthralgia in 8% of the vaccinees. There are five amino acid differences between the vaccine and its parent, as well as five synonymous mutations, none of which involves cis-acting genome regions known to be responsible for replication or packaging. To identify the determinants of attenuation, we therefore tested the five nonsynonymous mutations by cloning them individually or in different combinations into infectious clones derived from two wild-type (WT) CHIKV strains, La Reunion and AF15561. Levels of virulence were compared with those of the WT strains and the vaccine strain in two different murine models: infant CD1 and adult A129 mice. An attenuated phenotype indistinguishable from that of the 181/clone 25 vaccine strain was obtained by the simultaneous expression of two E2 glycoprotein substitutions, with intermediate levels of attenuation obtained with the single E2 mutations. The other three amino acid mutations, in nsP1, 6K, and E1, did not have a detectable effect on CHIKV virulence. These results indicate that the attenuation of strain 181/clone 25 is mediated by two point mutations, explaining the phenotypic instability observed in human vaccinees and also in our studies.

A vaccine candidate for eastern equine encephalitis virus based on IRES-mediated attenuation

To develop an effective vaccine against eastern equine encephalitis (EEE), we engineered a recombinant EEE virus (EEEV) that was attenuated and capable of replicating only in vertebrate cells, an important safety feature for live vaccines against mosquito-borne viruses. The subgenomic promoter was inactivated with 13 synonymous mutations and expression of the EEEV structural proteins was placed under the control of an internal ribosomal entry site (IRES) derived from encephalomyocarditis virus (EMCV). We tested this vaccine candidate for virulence, viremia and efficacy in the murine model. A single subcutaneous immunization with 10(4) infectious units protected 100% of mice against intraperitoneal challenge with a highly virulent North American EEEV strain. None of the mice developed any signs of disease or viremia after immunization or following challenge. Our findings suggest that the IRES-based attenuation approach can be used to develop a safe and effective vaccine against EEE and other alphaviral diseases.

Arbovirus vaccines; opportunities for the baculovirus-insect cell expression system

The baculovirus-insect cell expression system is a well-established technology for the production of heterologous viral (glyco)proteins in cultured cells, applicable for basic scientific research as well as for the development and production of vaccines and diagnostics. Arboviruses form an emerging group of medically important viral pathogens that are transmitted to humans and animals via arthropod vectors, mostly mosquitoes, ticks or midges. Few arboviral vaccines are currently available, but there is a growing need for safe and effective vaccines against some highly pathogenic arboviruses such as Chikungunya, dengue, West Nile, Rift Valley fever and Bluetongue viruses. This comprehensive review discusses the biology and current state of the art in vaccine development for arboviruses belonging to the families Togaviridae, Flaviviridae, Bunyaviridae and Reoviridae and the potential of the baculovirus-insect cell expression system for vaccine antigen production The members of three of these four arbovirus families have enveloped virions and display immunodominant glycoproteins with a complex structure at their surface. Baculovirus expression of viral antigens often leads to correctly folded and processed (glyco)proteins able to induce protective immunity in animal models and humans. As arboviruses occupy a unique position in the virosphere in that they also actively replicate in arthropod cells, the baculovirus-insect cell expression system is well suited to produce arboviral proteins with correct folding and post-translational processing. The opportunities for recombinant baculoviruses to aid in the development of safe and effective subunit and virus-like particle vaccines against arboviral diseases are discussed.

Squalamine as a broad-spectrum systemic antiviral agent with therapeutic potential

Antiviral compounds that increase the resistance of host tissues represent an attractive class of therapeutic. Here, we show that squalamine, a compound previously isolated from the tissues of the dogfish shark (Squalus acanthias) and the sea lamprey (Petromyzon marinus), exhibits broad-spectrum antiviral activity against human pathogens, which were studied in vitro as well as in vivo. Both RNA- and DNA-enveloped viruses are shown to be susceptible. The proposed mechanism involves the capacity of squalamine, a cationic amphipathic sterol, to neutralize the negative electrostatic surface charge of intracellular membranes in a way that renders the cell less effective in supporting viral replication. Because squalamine can be readily synthesized and has a known safety profile in man, we believe its potential as a broad-spectrum human antiviral agent should be explored.

Novel chikungunya vaccine candidate with an IRES-based attenuation and host range alteration mechanism

Chikungunya virus (CHIKV) is a reemerging mosquito-borne pathogen that has recently caused devastating urban epidemics of severe and sometimes chronic arthralgia. As with most other mosquito-borne viral diseases, control relies on reducing mosquito populations and their contact with people, which has been ineffective in most locations. Therefore, vaccines remain the best strategy to prevent most vector-borne diseases. Ideally, vaccines for diseases of resource-limited countries should combine low cost and single dose efficacy, yet induce rapid and long-lived immunity with negligible risk of serious adverse reactions. To develop such a vaccine to protect against chikungunya fever, we employed a rational attenuation mechanism that also prevents the infection of mosquito vectors. The internal ribosome entry site (IRES) from encephalomyocarditis virus replaced the subgenomic promoter in a cDNA CHIKV clone, thus altering the levels and host-specific mechanism of structural protein gene expression. Testing in both normal outbred and interferon response-defective mice indicated that the new vaccine candidate is highly attenuated, immunogenic and efficacious after a single dose. Furthermore, it is incapable of replicating in mosquito cells or infecting mosquitoes in vivo. This IRES-based attenuation platform technology may be useful for the predictable attenuation of any alphavirus.

Use of sindbis/eastern equine encephalitis chimeric viruses in plaque reduction neutralization tests for arboviral disease diagnostics

Eastern equine encephalitis virus (EEEV) is a highly virulent, mosquito-borne alphavirus that causes severe and often fatal neurological disease in humans and horses in eastern North American, the Caribbean, and Mexico and throughout Central and South America. EEEV infection is diagnosed serologically by anti-EEEV-specific IgM detection, with confirmation by the plaque reduction neutralization test (PRNT), which is highly specific for alphaviruses. Live virus is used in the PRNT procedure, which currently requires biosafety level 3 containment facilities and select agent security in the case of EEEV. These requirements restrict the ability of public health laboratories to conduct PRNTs. Sindbis virus (SINV)/EEEV recombinant constructs have been engineered to express the immunogenic structural proteins from 2 wild-type EEEV strains in an attenuated form. These SINV/EEEVs, which are not classified as select agents, were evaluated as alternative diagnostic reagents in a PRNT using human, equine, and murine sera. The results indicate that the chimeric viruses exhibit specificity comparable to that of wild-type EEEV, with only a slight reduction in sensitivity. Considering their benefits in increased safety and reduced regulatory requirements, these chimeric viruses should be highly useful in diagnostic laboratories throughout the Americas.

Conservation of a packaging signal and the viral genome RNA packaging mechanism in alphavirus evolution

Alphaviruses are a group of small, enveloped viruses which are widely distributed on all continents. In infected cells, alphaviruses display remarkable specificity in RNA packaging by encapsidating only their genomic RNA while avoiding packaging of the more abundant viral subgenomic (SG), cellular messenger and transfer RNAs into released virions. In this work, we demonstrate that in spite of evolution in geographically isolated areas and accumulation of considerable diversity in the nonstructural and structural genes, many alphaviruses belonging to different serocomplexes harbor RNA packaging signals (PSs) which contain the same structural and functional elements. Their characteristic features are as follows. (i) Sindbis, eastern, western, and Venezuelan equine encephalitis and most likely many other alphaviruses, except those belonging to the Semliki Forest virus (SFV) clade, have PSs which can be recognized by the capsid proteins of heterologous alphaviruses. (ii) The PS consists of 4 to 6 stem-loop RNA structures bearing conserved GGG sequences located at the base of the loop. These short motifs are integral elements of the PS and can function even in the artificially designed PS. (iii) Mutagenesis of the entire PS or simply the GGG sequences has strong negative effects on viral genome packaging and leads to release of viral particles containing mostly SG RNAs. (iv) Packaging of RNA appears to be determined to some extent by the number of GGG-containing stem-loops, and more than one stem-loop is required for efficient RNA encapsidation. (v) Viruses of the SFV clade are the exception to the general rule. They contain PSs in the nsP2 gene, but their capsid protein retains the ability to use the nsP1-specific PS of other alphaviruses. These new discoveries regarding alphavirus PS structure and function provide an opportunity for the development of virus variants, which are irreversibly attenuated in terms of production of infectious virus but release high levels of genome-free virions.

Probing the attenuation and protective efficacy of a candidate chikungunya virus vaccine in mice with compromised interferon (IFN) signaling

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that causes explosive outbreaks of febrile illness associated with rash, and painful arthralgia. The CHIK vaccine strain 181/clone25 (181/25) developed by the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) was shown to be well-tolerated and highly immunogenic in phase I and II clinical trials although it induced transient arthralgia in some healthy adult volunteers. In an attempt to better understand the host factors that are involved in the attenuating phenotype of CHIK 181/25 vaccine virus we conducted studies in interferon (IFN)-compromised mice and also evaluated its immunogenic potential and protective capacity. Infection of AG129 mice (defective in IFN-α/β and IFN-γ receptor signaling) with CHIK 181/25 resulted in rapid mortality within 3-4 days. In contrast, all infected A129 mice (defective in IFN-α/β receptor signaling) survived with temporary morbidity characterized by ruffled appearance and body weight loss. A129 heterozygote mice that retain partial IFN-α/β receptor signaling activity remained healthy. Infection of A129 mice with CHIK 181/25 induced significant levels of IFN-γ and IL-12 while the inflammatory cytokines, TNFα and IL-6 remained low. A single administration of the CHIK 181/25 vaccine provided both short-term and long-term protection (38 days and 247 days post-prime, respectively) against challenge with wt CHIKV-La Reunion (CHIKV-LR). This protection was at least partially mediated by antibodies since passively transferred immune serum protected both A129 and AG129 mice from wt CHIKV-LR and 181/25 virus challenge. Overall, these data highlight the importance of IFNs in controlling CHIK 181/25 vaccine and demonstrate the ability of this vaccine to elicit neutralizing antibody responses that confer short-and long-term protection against wt CHIKV-LR challenge.

Design of chimeric alphaviruses with a programmed, attenuated, cell type-restricted phenotype

The Alphavirus genus in the Togaviridae family contains a number of human and animal pathogens. The importance of alphaviruses has been strongly underappreciated; however, epidemics of chikungunya virus (CHIKV), causing millions of cases of severe and often persistent arthritis in the Indian subcontinent, have raised their profile in recent years. In spite of a continuous public health threat, to date no licensed vaccines have been developed for alphavirus infections. In this study, we have applied an accumulated knowledge about the mechanism of alphavirus replication and protein function in virus-host interactions to introduce a new approach in designing attenuated alphaviruses. These variants were constructed from genes derived from different, geographically isolated viruses. The resulting viable variants encoded CHIKV envelope and, in contrast to naturally circulating viruses, lacked the important contributors to viral pathogenesis: genes encoding proteins functioning in inhibition of cellular transcription and downregulation of the cellular antiviral response. To make these viruses incapable of transmission by mosquito vectors and to differentially regulate expression of viral structural proteins, their replication was made dependent on the internal ribosome entry sites, derived from other positive-polarity RNA (RNA(+)) viruses. The rational design of the genomes was complemented by selection procedures, which adapted viruses to replication in tissue culture and produced variants which (i) demonstrated different levels of replication and production of the individual structural proteins, (ii) efficiently induced the antiviral response in infected cells, (iii) were incapable of replication in cells of mosquito origin, and (iv) efficiently replicated in Vero cells. This modular approach to genome design is applicable for the construction of other alphaviruses with a programmed, irreversibly attenuated phenotype.

Stability of RNA virus attenuation approaches

The greatest risk from live-attenuated vaccines is reversion to virulence. Particular concerns arise for RNA viruses, which exhibit high mutation frequencies. We examined the stability of 3 attenuation strategies for the alphavirus, Venezuelan equine encephalitis virus (VEEV): a traditional, point mutation-dependent attenuation approach exemplified by TC-83; a rationally designed, targeted-mutation approach represented by V3526; and a chimeric vaccine, SIN/TC/ZPC. Our findings suggest that the chimeric strain combines the initial attenuation of TC-83 with the greater phenotypic stability of V3526, highlighting the importance of the both initial attenuation and stability for live-attenuated vaccines.

Principles of antidote pharmacology: an update on prophylaxis, post-exposure treatment recommendations and research initiatives for biological agents

The use of biological agents has generally been confined to military-led conflicts. However, there has been an increase in non-state-based terrorism, including the use of asymmetric warfare, such as biological agents in the past few decades. Thus, it is becoming increasingly important to consider strategies for preventing and preparing for attacks by insurgents, such as the development of pre- and post-exposure medical countermeasures. There are a wide range of prophylactics and treatments being investigated to combat the effects of biological agents. These include antibiotics (for both conventional and unconventional use), antibodies, anti-virals, immunomodulators, nucleic acids (analogues, antisense, ribozymes and DNAzymes), bacteriophage therapy and micro-encapsulation. While vaccines are commercially available for the prevention of anthrax, cholera, plague, Q fever and smallpox, there are no licensed vaccines available for use in the case of botulinum toxins, viral encephalitis, melioidosis or ricin. Antibiotics are still recommended as the mainstay treatment following exposure to anthrax, plague, Q fever and melioidosis. Anti-toxin therapy and anti-virals may be used in the case of botulinum toxins or smallpox respectively. However, supportive care is the only, or mainstay, post-exposure treatment for cholera, viral encephalitis and ricin - a recommendation that has not changed in decades. Indeed, with the difficulty that antibiotic resistance poses, the development and further evaluation of techniques and atypical pharmaceuticals are fundamental to the development of prophylaxis and post-exposure treatment options. The aim of this review is to present an update on prophylaxis and post-exposure treatment recommendations and research initiatives for biological agents in the open literature from 2007 to 2009.