A Novel Nonhuman Primate Model for Influenza Transmission

Studies of influenza transmission are necessary to predict the pandemic potential of emerging influenza viruses. Currently, both ferrets and guinea pigs are used in such studies, but these species are distantly related to humans. Nonhuman primates (NHP) share a close phylogenetic relationship with humans and may provide an enhanced means to model the virological and immunological events in influenza virus transmission. Here, for the first time, it was demonstrated that a human influenza virus isolate can productively infect and be transmitted between common marmosets (Callithrix jacchus), a New World monkey species. We inoculated four marmosets with the 2009 pandemic virus A/California/07/2009 (H1N1pdm) and housed each together with a naïve cage mate. We collected bronchoalveolar lavage and nasal wash samples from all animals at regular intervals for three weeks post-inoculation to track virus replication and sequence evolution. The unadapted 2009 H1N1pdm virus replicated to high titers in all four index animals by 1 day post-infection. Infected animals seroconverted and presented human-like symptoms including sneezing, nasal discharge, labored breathing, and lung damage. Transmission occurred in one cohabitating pair. Deep sequencing detected relatively few genetic changes in H1N1pdm viruses replicating in any infected animal. Together our data suggest that human H1N1pdm viruses require little adaptation to replicate and cause disease in marmosets, and that these viruses can be transmitted between animals. Marmosets may therefore be a viable model for studying influenza virus transmission.     

Latent Adeno-Associated Virus Infection Elicits Humoral but Not Cell-Mediated Immune Responses in a Nonhuman Primate Model

Latent infection with wild-type (wt) adeno-associated virus (AAV) was studied in rhesus macaques, a species that is a natural host for AAV and that has some homology to humans with respect to the preferred locus for wt AAV integration. Each of eight animals was infected with an inoculum of 10(10) IU of wt AAV, administered by either the intranasal, intramuscular, or intravenous route. Two additional animals were infected intranasally with wt AAV and a helper adenovirus (Ad), while one additional animal was inoculated with saline intranasally as a control. There were no detectable clinical or histopathologic responses to wt AAV administration. Molecular analyses, including Southern blot, PCR, and fluorescence in situ hybridization, were performed 21 days after infection. These studies indicated that AAV DNA sequences persisted at the sites of administration, albeit at low copy number, and in peripheral blood mononuclear cells. Site-specific integration into the AAVS1-like locus was observed in a subset of animals. All animals, except those infected by the intranasal route with wt AAV alone, developed a humoral immune response to wt AAV capsid proteins, as evidenced by a >/=fourfold rise in anti-AAV neutralizing titers. However, only animals infected with both wt AAV and Ad developed cell-mediated immune responses to AAV capsid proteins. These findings provide some insights into the nature of anti-AAV immune responses that may be useful in interpreting results of future AAV-based gene transfer studies.     

Development of a Nonhuman Primate Model for Fetoscopy

Twenty-four fetoscopy procedures were performed on 22 monkeys (19 Macaca mulatto, one M. fascicularis, two Erythrocebus patas) with gestational ages ranging from 66 to 145 days. Insertion of the fetoscope without ultrasound guidance was easy in 14 and difficult in ten procedures. Amniotic fluid exchange with normal saline, to improve visualization, was successful in eight of 13 procedures. Fetal blood sampling was successful in four of nine attempts. Nine monkeys aborted within 17 days of the fetoscopy, the remaining 13 went to term or were used in other research protocols. Major complications included maternal hemorrhage into the amniotic fluid, inability to enter the amniotic cavity, and abortion. Maternal serum alpha-fetoprotein following fetoscopy was not a useful indicator of subsequent abortion.     

A Mouse Model of Lethal Infection for Evaluating Prophylactics and Therapeutics against Monkeypox Virus

Monkeypox virus (MPXV) is an orthopoxvirus closely related to variola, the etiological agent of smallpox. In humans, MPXV causes a disease similar to smallpox and is considered to be an emerging infectious disease. Moreover, the use of MPXV for bioterroristic/biowarfare activities is of significant concern. Available small animal models of human monkeypox have been restricted to mammals with poorly defined biologies that also have limited reagent availability. We have established a murine MPXV model utilizing the STAT1-deficient C57BL/6 mouse. Here we report that a relatively low-dose intranasal (IN) infection induces 100% mortality in the stat1^−/− model by day 10 postinfection with high infectious titers in the livers, spleens, and lungs of moribund animals. Vaccination with modified vaccinia virus Ankara (MVA) followed by a booster vaccination is sufficient to protect against an intranasal MPXV challenge and induces an immune response more robust than that of a single vaccination. Furthermore, antiviral treatment with CMX001 (HDP-cidofovir) and ST-246 protects when administered as a regimen initiated on the day of infection. Thus, the stat1^−/− model provides a lethal murine platform for evaluating therapeutics and for investigating the immunological and pathological responses to MPXV infection.During the early smallpox-free epoch, the orthopoxviruses were of minor bioterroristic concern due to the largely vaccinated population; however, this has changed with the increased risk of bioterrorism, and variola virus (VARV) and monkeypox virus (MPXV) are considered to have significant potential to become bioterror agents (36, 37). VARV, the etiological agent of smallpox, is officially stored at two WHO secure laboratories in the United States and Russia; however, there is concern that covert stocks exist. Furthermore, we are currently faced with the possibility of intentional release of wild-type or genetically modified VARV. Of most concern would be viruses encoding human interleukin-4 (IL-4), which could significantly increase virulence, as demonstrated with the mousepox/ectromelia virus (ECTV) model (18). As a result of the cessation of routine vaccination and the high number of individuals that are contraindicated for vaccination, the human population lacks solid “herd immunity” to naturally circulating orthopoxviruses. One such virus that is of particular concern is MPXV, due to its ability to infect humans, its mortality rate of approximately 10% (depending on the strain), its propensity to infect a large number of species, its apparently increasing transmissibility in the human population, and its reportedly expanding host range (36). One such example of increasing host range was observed during 2003 in the United States, where imported African rodents transmitted MPXV to native prairie dogs, which acted as an “amplification reservoir” that allowed for the transmission of MPXV to humans (14).To date, MPXV animal models for efficacy testing of prophylactics and therapeutics have been restricted to nonhuman primates and nonmurine small animal models, such as the 13-lined ground squirrel (Spermophilus tridecemlineatus) (49, 55), the black-tailed prairie dog (Cynomys ludovicianus) (14, 17, 22, 60), and the African dormouse (Graphiurus kelleni) (50). Because the ground squirrel and the prairie dog are difficult to propagate, have low fecundity rates, and have complex husbandry requirements, they must be obtained from their natural habitat and therefore have unknown health statuses (16, 58). Conversely, the African dormouse has many characteristics similar to those of laboratory mice and can be easily propagated in a research vivarium. The disadvantage to this model is that there are few commercially available reagents for characterizing the animals'' response to infection, and their biology is poorly understood (50).Suckling white mice have been shown to be highly susceptible to MPXV inoculations by various routes. Eight-day-old white mice developed disease and died following intraperitoneal or intranasal (IN) inoculations with 1.2 × 10⁶ PFU. Injection into the footpad also induced severe disease and death following 6 × 10² PFU inoculations. Disease symptoms included flabbiness; loss of appetite; and following footpad infections, edema of the foot. Similar symptoms were observed following inoculation by the oral route, which induced 40% lethality. Intradermal inoculations with MPXV resulted in 50% death. The intranasal route of infection was determined to induce the highest level of lethality, causing 100% death in mice as old as 15 days, compared to only 14% and 60% lethality in 12-day-old mice infected orally or via the footpad, respectively (24, 51). Recently, Osorio et al. showed that 4-week-old SCID-BALB/c mice are susceptible to 10⁵ PFU intraperitoneal (IP) MPXV inoculations, resulting in a mean day of death of 9 days postinfection (p.i.) (33). Unfortunately the IP route of infection does not model the natural transmission route of MPXV.Several factors make young (<15 days old) white mice a poor choice for studying MPXV. First, mice do not become fully immunocompetent until approximately 4 or 5 weeks old; therefore, the opportunity to study the immune response to infection is hampered. Moreover, immunoimmature animals cannot be used as models to study MPXV infections in immunocompetent humans. Second, a functioning immune system works in synergy with antiviral therapies to provide protection against viral challenge; thus, antiviral efficacy cannot be properly evaluated. Third, the relatively short susceptible time window of birth to 15 days old makes large-scale experiments impractical. Fourthly, young immunoimmature mice cannot be used to study vaccination efficacy. To this end, we sought to identify adult mice that are susceptible to lethal MPXV challenges and can be used for antiviral and vaccination efficacy studies.In the present study we found that most common strains of adult immunocompetent laboratory mice are resistant to MPXV. We also found that type 1 and type 2 interferon (IFN) receptor-null mice were resistant. Because strains lacking STAT1, a key protein involved in type 1 and 2 IFN signaling networks, have been shown to be sensitive to a wide number of viral and bacterial infections (13, 15, 30, 46, 52-54), we evaluated their sensitivities to MPXV challenges. We found that C57BL/6 mice lacking stat1 (C57BL/6 stat1^−/−) were highly sensitive to MPXV and that 129 mice lacking stat1 were sensitive but to a lesser degree than the C57BL/6 stat1^−/− animals. In this report, we show that the disease course in MPXV-infected C57BL/6 stat1^−/− mice, that is, weight loss and death by day 10 postinfection, is similar to that observed in wild-type mice infected with ECTV, the etiological agent of mousepox (11). Further, we reveal that antiviral therapy with CMX001 or ST-246 protects mice to a degree similar to that of vaccination with Dryvax or modified vaccinia virus Ankara (MVA), supporting the use of the C57BL/6 stat1^−/− as a model to evaluate orthopoxvirus prophylactics and therapeutics.     

A Novel Model of Lethal Hendra Virus Infection in African Green Monkeys and the Effectiveness of Ribavirin Treatment

The henipaviruses, Hendra virus (HeV) and Nipah virus (NiV), are emerging zoonotic paramyxoviruses that can cause severe and often lethal neurologic and/or respiratory disease in a wide variety of mammalian hosts, including humans. There are presently no licensed vaccines or treatment options approved for human or veterinarian use. Guinea pigs, hamsters, cats, and ferrets, have been evaluated as animal models of human HeV infection, but studies in nonhuman primates (NHP) have not been reported, and the development and approval of any vaccine or antiviral for human use will likely require efficacy studies in an NHP model. Here, we examined the pathogenesis of HeV in the African green monkey (AGM) following intratracheal inoculation. Exposure of AGMs to HeV produced a uniformly lethal infection, and the observed clinical signs and pathology were highly consistent with HeV-mediated disease seen in humans. Ribavirin has been used to treat patients infected with either HeV or NiV; however, its utility in improving outcome remains, at best, uncertain. We examined the antiviral effect of ribavirin in a cohort of nine AGMs before or after exposure to HeV. Ribavirin treatment delayed disease onset by 1 to 2 days, with no significant benefit for disease progression and outcome. Together our findings introduce a new disease model of acute HeV infection suitable for testing antiviral strategies and also demonstrate that, while ribavirin may have some antiviral activity against the henipaviruses, its use as an effective standalone therapy for HeV infection is questionable.Hendra virus (HeV) and Nipah virus (NiV) are members of the genus Henipavirus (family Paramyxoviridae) that can cause severe respiratory illness and/or encephalitis in a wide variety of mammals, including horses, pigs, and humans (7, 23). HeV was identified as the causative agent of an acute respiratory disease in horses in 1994 in Queensland, Australia (23), and to date there have been 14 outbreaks in Australia since, with at least one occurrence per year since 2006, most recently in May 2010 (ProMed-mail no. 20100522.1699 [International Society for Infectious Diseases, http://www.promedmail.org]). Every outbreak of HeV has involved horses as the initial infected host, and there have been a total of seven human cases arising from exposure to infected horses. Four human fatalities have occurred (22), with the most recent occurring in August of 2009 (ProMed-mail no. 20090826.2998 and 20090903.3098). All patients initially presented with influenza-like illnesses (ILIs) after an incubation period of 7 to 16 days. While two individuals recovered from ILI, one patient developed pneumonitis and died from multiorgan failure. Three of the lethal cases developed encephalitic manifestations (mild confusion and ataxia), with two patients experiencing seizures (22, 23, 27).Data on the histopathology of fatal human HeV cases are limited, but the pathology includes small necrotic plaques in the cerebrum and cerebellum, in addition to mild parenchymal inflammation (21, 27). Severe parenchymal inflammation and necrosis were observed in the lungs. More extensive histopathologic data are available from 32 autopsies of fatal human NiV cases (28). Similarly to the HeV cases, pathology was characterized by systemic vasculitis and parenchymal necrosis in the central nervous system (CNS), while in the lung, pathological findings mainly included vasculitis, fibrinoid necrosis, alveolar hemorrhage, pulmonary edema, and aspiration pneumonia. Other organs that were affected included heart, kidney, and spleen and showed generally mild or focal inflammation. The development of syncytial multinucleated endothelial cells is characteristic of both HeV and NiV (27, 28). At present, the details of the pathogenesis and histopathological changes mediated by either HeV or NiV infection in humans are naturally derived from only the late phases of the disease course, and therefore a relevant animal model is needed that mimics the disease progression seen in humans.Pteropid fruit bats, commonly known as flying foxes in the family Pteropodidae, are the principle natural reservoirs for both NiV and HeV (reviewed in reference 3). However, these henipaviruses display a broad species tropism, and in addition to bats, horses and humans, natural and/or experimental infection of HeV has been demonstrated in guinea pigs, hamsters, pigs, cats, and ferrets (25). Experimental infections of Syrian hamsters with HeV is lethal, and animals show disease similar to that of human cases, including respiratory and neurological symptoms, depending on the dose (11; unpublished data). In this model, viral RNA can be detected in various organs of infected hamsters, including brain, lung, kidney, heart, liver, and spleen. The main histopathological findings included parenchymal infection in various organs, including the brain, with vasculitis and syncytial multinucleated endothelial cells in many blood vessels (11). While this model is useful in studying pathogenesis, it is limited in the availability of reagents to do so.There are currently no vaccines or treatments licensed for human use. Several in vitro studies have shown that ribavirin is effective against both HeV and NiV infection (1, 2, 29). An open-label ribavirin treatment trial was run during an outbreak of NiV in Malaysia in 1998 and reported to reduce mortality by 36% (6). Of the seven recorded human HeV cases, three patients were treated with ribavirin, one of whom survived (22). In the most recent outbreak of HeV in Australia, three additional people received ribavirin treatment in combination with chloroquine after suspected exposure to HeV-contaminated secretions from infected horses. While all three individuals survived, infection was not confirmed, and therefore it remains unknown whether the treatment had any beneficiary effect (ProMed-mail no. 20090826.2998). In addition, two animal studies in hamsters showed that ribavirin treatment delays but does not prevent death from NiV or HeV infection (8, 10). Therefore, an animal model with greater relevance to humans and that recapitulates the disease processes seen in human cases of HeV is needed to get a better answer to whether ribavirin might be effective against henipavirus infections. In addition, the U.S. FDA implemented the “Animal Efficacy Rule,” which specifically applies to the development of therapeutic products when human efficacy studies are not possible or ethical, such as is often the case with highly virulent pathogens like HeV (24). Essentially, this rule allows for the evaluation of vaccines or therapeutics using data derived from studies carried out in at least two animal models. The licensure of any therapeutic modalities for HeV will require a thorough evaluation of HeV pathogenesis in nonhuman primates (NHPs).In the present study, we report the development and characterization of a new nonhuman primate (NHP) model of lethal HeV infection in the African green monkey (AGM). The pathogenesis and disease progression in the AGM upon HeV infection essentially mirrored the lethal disease episodes seen among human cases of HeV. Using this new model, the efficacy of ribavirin treatment against lethal challenge with HeV was examined. Here we have shown that ribavirin treatment can significantly delay but not prevent death of AGMs from lethal HeV infection. In addition to severe respiratory symptoms in all animals, prolonged disease progression in ribavirin-treated animals was also marked by the appearance of neurological symptoms.     

Mice Lacking Functional STAT1 Are Highly Susceptible to Lethal Infection with Lassa Virus

Lassa fever (LF) is a potentially lethal human disease that is caused by the arenavirus Lassa virus (LASV). Annually, around 300,000 infections with up to 10,000 deaths occur in regions of Lassa fever endemicity in West Africa. Here we demonstrate that mice lacking a functional STAT1 pathway are highly susceptible to infection with LASV and develop lethal disease with pathology similar to that reported in humans.     

Nonhuman Primate Behavior: A Note on Recent Research

Recent publications dealing with nonhuman primate social behavior suggest that Service's discussion of that topic in The Hunters is in need of extensive revision, and that Damas's (AA 71:315–316) recently expressed admiration for the discussion is unfortunate. Short paragraphs based on readily available references summarize findings that have appeared since The Hunters was published and indicate where Service's generalizations concerning species specific social organization, sexual seasonality, dominance orders, and territoriality are in greatest need of updating. [Primate social behavior; hunter-gatherers; ecological studies]     

Acute Neuronal Injury and Blood Genomic Profiles in a Nonhuman Primate Model for Ischemic Stroke

The goal of this study was to characterize acute neuronal injury in a novel nonhuman primate (NHP) ischemic stroke model by using multiple outcome measures. Silk sutures were inserted into the M1 segment of the middle cerebral artery of rhesus macaques to achieve permanent occlusion of the vessel. The sutures were introduced via the femoral artery by using endovascular microcatheterization techniques. Within hours after middle cerebral artery occlusion (MCAO), infarction was detectable by using diffusion-weighted MRI imaging. The infarcts expanded by 24 h after MCAO and then were detectable on T2-weighted images. The infarcts seen by MRI were consistent with neuronal injury demonstrated histologically. Neurobehavioral function after MCAO was determined by using 2 neurologic testing scales. Neurologic assessments indicated that impairment after ischemia was limited to motor function in the contralateral arm; other neurologic and behavioral parameters were largely unaffected. We also used microarrays to examine gene expression profiles in peripheral blood mononuclear cells after MCAO-induced ischemia. Several genes were altered in a time-dependent manner after MCAO, suggesting that this ischemia model may be suitable for identifying blood biomarkers associated with the presence and severity of ischemia. This NHP stroke model likely will facilitate the elucidation of mechanisms associated with acute neuronal injury after ischemia. In addition, the ability to identify candidate blood biomarkers in NHP after ischemia may prompt the development of new strategies for the diagnosis and treatment of ischemic stroke in humans.Abbreviations: MCAO, middle cerebral artery occlusion; NHP, nonhuman primate; PBMC, peripheral blood mononuclear cellsStroke is a debilitating neurologic condition, and little progress has been made in the development of neuroprotective treatments for acute stroke. The Stroke Therapy Academic Industry Roundtable (STAIR) report suggested that preclinical candidates for stroke therapy should be validated by testing in large animals with similarities to humans, such as nonhuman primates (NHP).²⁶ NHP stroke models have been developed in several species, including rhesus monkeys, marmosets, and baboons, by using a variety of techniques for middle cerebral artery occlusion (MCAO).^{4,10,12,13,14,25,32} The rhesus macaque is ideal for stroke studies because of its structural similarities to human brain. The rhesus brain is gyrencephalic, which makes it preferable to those of lissencephalic primates (for example, marmosets) and is functionally similar to human brain.⁶ In addition, the immunologic profile of rhesus macaques is similar to that of humans; therefore these animals are the preferred model for the study of immune responses to infectious diseases such as HIV/SIV, Dengue virus, and others.^17,23,30In addition to their use for neuroprotection assessment, NHP stroke models can facilitate efforts to develop diagnostic tools for identifying and treating stroke symptoms. The use of genomics in peripheral blood cells has been shown to be an excellent method to identify candidate biomarkers and cellular mechanisms associated with stroke.^28,29 Blood biomarkers can be used to rapidly determine the occurrence, timing, subtype, and severity of stroke.^11,15 One possible reason for the lack of viable stroke biomarkers may be the research models used to search for these markers. Although rodent stroke models have yielded a wealth of information on the mechanisms associated with brain ischemia, the findings have not translated well to human clinical trials.²⁶ Recent studies in human patients showed promising results when genomic tools have been used to screen for novel stroke biomarkers.^3,16,27 However, validation of human studies is limited by the need for large data sets in light of heterogeneity in stroke onset, subtype, comorbidities, and other factors. In addition, it is also impossible to know the exact time of stroke onset in most patients.Here we characterized acute neuronal injury in a novel, minimally invasive permanent ischemic stroke model involving rhesus macaques. Using endovascular catheterization techniques, we introduced silk sutures into the M1 segment of the middle cerebral artery and permanently occluded it. This procedure reliably produced infarcts that could be measured by MRI of the macaque brains during the acute phase period. The procedure resulted in discrete and limited neurobehavioral deficits, indicating the potential of this stroke model for chronic neuroprotection studies in the future. In addition, we used microarrays to identify blood genomic profiles that were altered in a time-dependent manner after ischemia. These studies characterize a preclinical model that is suitable for elucidating the mechanisms associated with cerebral ischemia and that may aid in identifying strategies for the diagnosis and treatment of stroke in humans.     

Feasibility and Uncertainty in Behavior Genetics for the Nonhuman Primate

The analysis of phenotypic covariances among genetically related individuals is the basis for estimations of genetic and phenotypic effects on phenotypes. Beyond heritability, there are several other estimates that can be made with behavior genetic models of interest to primatologists. Some of these estimates are feasible with primate samples because they take advantage of the types of relatives available to compare in primate species and because most behaviors are expressed orders of magnitude more often and in a greater variety of contexts than morphological or life-history traits. The hypotheses that can be tested with these estimates are contrasted with hypotheses that will be difficult to achieve in primates because of sample size limitations. Feasible comparisons include the proportion of variance from interaction effects, the variation of genetic effects across environments, and the genetics of growth and development. Simulation shows that uncertainty of genetic parameters can be reduced by sampling each individual more than once. Because sample sizes are likely to remain relatively small in most primate behavior genetics, expressing uncertainty in parameter estimates is needed to move our inferences forward.     

The Baboon as a Nonhuman Primate Model for the Study of the Genetics of Obesity

Objective: At present, rodents represent the most common animal model for research in obesity and its comorbidities (e.g., type 2 diabetes and coronary heart disease), however, there are several physiological and developmental differences between rodents and humans reflective of their relatively ancient evolutionary divergence (approximately 65 to 75 million years ago). Therefore, we are currently developing the baboon as a nonhuman primate model for the study of the genetics of obesity. Research Methods and Procedures: At present, we are collecting extensive phenotypic data in a large pedigreed colony (N > 2000) of baboons housed at the Southwest Foundation for Biomedical Research in San Antonio, Texas. The long‐term goal of this project is to identify genes influencing adiposity‐related phenotypes and to test hypotheses regarding their pleiotropic effects on other phenotypes related to increased risk for a variety of common diseases (e.g., coronary heart disease and type 2 diabetes). Results: To date we have obtained various adipose‐specific endocrine measures, adipose tissue biopsies, and estimates of body composition on a substantial portion of our pedigreed colony. The pattern of adipose tissue accumulation follows closely that seen in humans, and we have detected significant additive genetic heritabilities for these obesity‐related phenotypes. Discussion: Given the physiological and developmental similarities between humans and baboons, along with the ability to collect data under well‐controlled situations and the extensive pedigree data available in our colony, the baboon offers an extremely valuable nonhuman primate model for the study of obesity and its comorbidities.     

Rabbit as a Novel Animal Model for Hepatitis E Virus Infection and Vaccine Evaluation

Background

The identification of hepatitis E virus (HEV) from rabbits motivated us to assess the possibility of using rabbits as a non-human primate animal model for HEV infection and vaccine evaluation.

Methodology/Principal Findings

First, 75 rabbits were inoculated with seven strains of genotypes 1, 3, 4, and rabbit HEV, to determine the appropriate strain, administrative route and viral dosage. Second, 15 rabbits were randomly divided into three groups and vaccinated with 0 µg (placebo), 10 µg and 20 µg of HEV candidate vaccine, HEV p179, respectively. After three doses of the vaccination, the rabbits were challenged with 3.3×10⁵ genome equivalents of genotype 4 HEV strain H4-NJ703. The strain of genotype 1 HEV was not found to be infectious for rabbits. However, approximately 80% of the animals were infected by two rabbit HEV strains. All rabbits inoculated with a genotype 3 strain were seroconverted but did not show viremia or fecal viral shedding. Although two genotype 4 strains, H4-NJ153 and H4-NJ112, only resulted in part of rabbits infected, another strain of genotype 4, H4-NJ703, had an infection rate of 100% (five out of five) when administrated intravenously. However, only two out of fifteen rabbits showed virus excretion and seroconversion when inoculated orally with H4-NJ703 of three different dosages. In the vaccine evaluation study, rabbits vaccinated with 20 µg of the HEV p179 produced anti-HEV with titers of 1∶10⁴–1∶10⁵ and were completely protected from infection. Rabbits vaccinated with 10 µg produced anti-HEV with titers of 1∶10³–1∶10⁴ and were protected from hepatitis, but two out of the five rabbits showed virus shedding.

Conclusions/Significance

Rabbits may be served as an alternative to the non-human primate models for HEV infection and vaccine evaluation when certain virus strains, appropriate viral dosages, and the intravenous route of inoculation are selected.     

Single-Injection Vaccine Protects Nonhuman Primates against Infection with Marburg Virus and Three Species of Ebola Virus

The filoviruses Marburg virus and Ebola virus cause severe hemorrhagic fever with high mortality in humans and nonhuman primates. Among the most promising filovirus vaccines under development is a system based on recombinant vesicular stomatitis virus (VSV) that expresses a single filovirus glycoprotein (GP) in place of the VSV glycoprotein (G). Here, we performed a proof-of-concept study in order to determine the potential of having one single-injection vaccine capable of protecting nonhuman primates against Sudan ebolavirus (SEBOV), Zaire ebolavirus (ZEBOV), Cote d''Ivoire ebolavirus (CIEBOV), and Marburgvirus (MARV). In this study, 11 cynomolgus monkeys were vaccinated with a blended vaccine consisting of equal parts of the vaccine vectors VSVΔG/SEBOVGP, VSVΔG/ZEBOVGP, and VSVΔG/MARVGP. Four weeks later, three of these animals were challenged with MARV, three with CIEBOV, three with ZEBOV, and two with SEBOV. Three control animals were vaccinated with VSV vectors encoding a nonfilovirus GP and challenged with SEBOV, ZEBOV, and MARV, respectively, and five unvaccinated control animals were challenged with CIEBOV. Importantly, none of the macaques vaccinated with the blended vaccine succumbed to a filovirus challenge. As expected, an experimental control animal vaccinated with VSVΔG/ZEBOVGP and challenged with SEBOV succumbed, as did the positive controls challenged with SEBOV, ZEBOV, and MARV, respectively. All five control animals challenged with CIEBOV became severely ill, and three of the animals succumbed on days 12, 12, and 14, respectively. The two animals that survived CIEBOV infection were protected from subsequent challenge with either SEBOV or ZEBOV, suggesting that immunity to CIEBOV may be protective against other species of Ebola virus. In conclusion, we developed an immunization scheme based on a single-injection vaccine that protects nonhuman primates against lethal challenge with representative strains of all human pathogenic filovirus species.Marburgvirus (MARV) and Ebolavirus (EBOV), the causative agents of Marburg and Ebola hemorrhagic fever (HF), respectively, represent the two genera that comprise the family Filoviridae (8, 24). The MARV genus contains a single species, Lake Victoria marburgvirus. The EBOV genus is divided into four distinct species: (i) Sudan ebolavirus (SEBOV), (ii) Zaire ebolavirus (ZEBOV), (iii) Cote d''Ivoire ebolavirus (CIEBOV), and (iv) Reston ebolavirus (REBOV). A putative fifth species of EBOV was associated with an outbreak in Uganda late in 2007 (33). MARV, ZEBOV, and SEBOV are important human pathogens, with case fatality rates frequently ranging between 70% and 90% for ZEBOV, around 50% for SEBOV, and up to 90% for MARV outbreaks depending on the strain of MARV (reviewed in reference 24). CIEBOV caused deaths in chimpanzees and a severe nonlethal human infection in a single case in the Republic of Cote d''Ivoire in 1994 (21). REBOV is highly lethal for macaques but is not thought to cause disease in humans, although the pathogenic potential of REBOV in humans remains unknown (24). An outbreak of REBOV in pigs was recently reported in the Philippines; however, it is unclear whether the disease observed in the pigs was caused by REBOV or other agents detected in the animals, including porcine reproductive and respiratory syndrome virus (5, 22).While there are no FDA-approved vaccines or postexposure treatment modalities available for preventing or managing EBOV or MARV infections, there are at least five different vaccine systems that have shown promise in completely protecting nonhuman primates against EBOV, and four of these systems have also been shown to protect macaques against MARV HF (3, 6, 12, 18, 20, 28-31, 35). Several of these vaccine platforms require multiple injections to confer protective efficacy (3, 18, 30, 31, 35). However, for agents such as EBOV and MARV, which are indigenous to Africa and are also potential agents of bioterrorism, a single-injection vaccine is preferable. In the case of preventing natural infections, multiple-dose vaccines are both too costly and not practicable (logistics and compliance) in developing countries. In the case of a deliberate release of these agents, there would be little time for deployment of a vaccine that requires multiple injections. Thus, for most practical applications, a vaccine against the filoviruses necessitates a single immunization.Of the prospective filovirus vaccines, only two systems, one based on a replication-defective adenovirus serotype 5 and the other based on the recombinant vesicular stomatitis virus (VSV), were shown to provide complete protection to nonhuman primates when administered as a single-injection vaccine (6, 12, 20, 28, 29). Most intriguingly, the VSV-based vaccine is the only vaccine which has shown utility when administered as a postexposure treatment against filovirus infections (7, 9, 15). Here, we evaluated the utility of combining our VSV-based EBOV and MARV vectors into a single-injection vaccine and determined the ability of this blended vaccine to protect nonhuman primates against three species of EBOV and MARV. Furthermore, we assessed the reusability of the VSV vectors in our macaque models of filovirus HF.