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Plasma membrane lipids and parainfluenza virus assembly
Hans-DieterKlenk Purnell W.Choppin
"With few exceptions, the lipids of virions closely resemble those of the plasma membrane of the cell in which the virus was grown. The results indicate that, in general, the virions acquire the lipid pattern of the plasma membrane of the host cell. "
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Susceptibility to superinfection of simian cells transformed by SV40
Characterization of a stable line of African green monkey kidney cells (BSC-1) transformed by SV40 was undertaken to determine whether these cells were resistant to superinfection by the homologous virus. The transformed cells were shown to synthesize the SV40-specific tumor antigen, the surface antigen, and the transplantation rejection antigen; SV40 capsid antigen was not detected. Infectious SV40 could not be recovered even after fusion of the transformed cells with cells susceptible to SV40 replication. Human adenovirus types 2, 7, and 12 replicated in the cells (but not in the parental, nontransformed cells), indicating either that the portion of the SV40 genome which aids the replication of human adenoviruses in simian cells was present in the transformed cells or that an adenovirus-sensitive cell population had been selected. However, SV40 was unable to replicate in the transformed cells, although simian adenovirus 7 and herpes viruses types 1 and 2 replicated in both parental and transformed cells.
A defective SV40 genome encapsidated in an adenovirus coat (PARA particle) was used to further analyze the ability of the transformed cell to replicate the superinfecting SV40 genome. Since replication of PARA particles occurred, a defective SV40 genome can be replicated in an SV40-transformed cell. Unresolved is the question concerning expression of late virus functions in these cells as PARA is defective in the ability to induce the synthesis of SV40 capsid protein.
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Whole genome molecular phylogeny of large dsDNA viruses using composition vector method
Abstract
Background: One important mechanism by which large DNA viruses increase their genome size
is the addition of modules acquired from other viruses, host genomes or gene duplications.
Phylogenetic analysis of large DNA viruses, especially using methods based on alignment, is often
difficult due to the presence of horizontal gene transfer events. The recent composition vector
approach, not sensitive to such events, is applied here to reconstruct the phylogeny of 124 large
DNA viruses.
Results: The results are mostly consistent with the biologist's systematics with only a few outliers
and can also provide some information for those unclassified viruses and cladistic relationships of
several families.
Conclusion: With composition vector approach we obtained the phylogenetic tree of large DNA
viruses, which not only give results comparable to biologist's systematics but also provide a new
way for recovering the phylogeny of viruses.
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Association of KIR2DS1 and KIR2DS3 with fatal outcome in Ebola virus infection
Zaďre ebolavirus (ZEBOV) infection rapidly outruns the host's immunity and leads to death within a week. Fatal cases have been associated with an aberrant innate, proinflammatory immune response followed by a suppressed adaptive response leading to the rapid depletion of peripheral NK cells and lymphocytes. A critical role for NK cells has been suggested but not elucidated. In this genetic study, we investigated the association of KIR genotype with disease outcome by comparing genotypes of a Gabonese control population, IgG+ contacts, survivors, and fatalities of ZEBOV infection. We showed that the activating KIR2DS1 and KIR2DS3 genes associate with fatal outcome in Ebola virus infection. In addition, this study brings supplemental evidence in favor of the specificity of the IgG+ contact population. The outcome of fulminating Ebola virus infection could depend in part on the host's inherited KIR gene repertoire. This supports a key role for KIRs in disease susceptibility to infections.
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Structure Unifies the Viral Universe
Is it possible to meaningfully comprehend the diversity of the viral
world? We propose that it is. This is based on the observation that,
although there is immense genomic variation, every infective virion is
restricted by strict constraints in structure space (i.e., there are a limited
number of ways to fold a protein chain, and only a small subset of these
have the potential to construct a virion, the hallmark of a virus). We have
previously suggested the use of structure for the higher-order classifi-
cation of viruses, where genomic similarities are no longer observable.
Here, we summarize the arguments behind this proposal, describe the
current status of structural work, highlighting its power to infer common
ancestry, and discuss the limitations and obstacles ahead of us. We
also reflect on the future opportunities for a more concerted effort to
provide high-throughput methods to facilitate the large-scale sampling
of the virosphere.
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Antigenic Subversion: A Novel Mechanism of Host Immune Evasion by Ebola Virus
In addition to its surface glycoprotein (GP1,2), Ebola virus (EBOV) directs the production of large quantities of a truncated glycoprotein isoform (sGP) that is secreted into the extracellular space. The generation of secreted antigens has been studied in several viruses and suggested as a mechanism of host immune evasion through absorption of antibodies and interference with antibody-mediated clearance. However such a role has not been conclusively determined for the Ebola virus sGP. In this study, we immunized mice with DNA constructs expressing GP1,2 and/or sGP, and demonstrate that sGP can efficiently compete for anti-GP12 antibodies, but only from mice that have been immunized by sGP. We term this phenomenon “antigenic subversion”, and propose a model whereby sGP redirects the host antibody response to focus on epitopes which it shares with membrane-bound GP1,2, thereby allowing it to absorb anti-GP1,2 antibodies. Unexpectedly, we found that sGP can also subvert a previously immunized host's anti-GP1,2 response resulting in strong cross-reactivity with sGP. This finding is particularly relevant to EBOV vaccinology since it underscores the importance of eliciting robust immunity that is sufficient to rapidly clear an infection before antigenic subversion can occur. Antigenic subversion represents a novel virus escape strategy that likely helps EBOV evade host immunity, and may represent an important obstacle to EBOV vaccine design.
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Bat-to-human: spike features determining ‘host jump’ of coronaviruses SARS-CoV, MERS-CoV, and beyond
Highlights
- Bats are natural reservoirs of many coronaviruses that can infect humans.
- Mechanisms of cross-species transmission of coronaviruses are important scientific questions.
- The coronaviral spike protein is an important viral determinant of cross-species transmission.
- Receptor-binding characteristics and cleavage priming of the spike protein are summarized.
Both severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) are zoonotic pathogens that crossed the species barriers to infect humans. The mechanism of viral interspecies transmission is an important scientific question to be addressed. These coronaviruses contain a surface-located spike (S) protein that initiates infection by mediating receptor-recognition and membrane fusion and is therefore a key factor in host specificity. In addition, the S protein needs to be cleaved by host proteases before executing fusion, making these proteases a second determinant of coronavirus interspecies infection. Here, we summarize the progress made in the past decade in understanding the cross-species transmission of SARS-CoV and MERS-CoV by focusing on the features of the S protein, its receptor-binding characteristics, and the cleavage process involved in priming.
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Virulence genes of Rickettsia rickettsii are differentially modulated by upshift or blood-feeding in tick midgut and salivary glands
Abstract
Background: Rickettsia rickettsii, the etiological agent of Rocky Mountain spotted fever, is transmitted to humans byticks. During tick feeding, R. rickettsii is exposed to both temperature elevation and components of the blood meal,which have previously been associated with the reactivation of its virulence. These environmental stimuli were alsoreported to modulate virulence genes of R. rickettsii infecting a set of organs of adult females of its natural vector,Amblyomma aureolatum.
Methods:
In this study, we determined the effects of a temperature upshift, blood-feeding, and both stimulisimultaneously on the expression of 85 selected genes of R. rickettsii infecting either the midgut (MG) or salivaryglands (SG) of male and female A. aureolatum by microfluidic high-throughput RT-qPCR. These two organs are keyfor acquisition of this bacterium by the tick and transmission to the vertebrate host, respectively.
Results: Data showed that these environmental stimuli exert distinct effects on rickettsial transcription dependingon the colonized organ and gender of the vector. Temperature upshift induced the majority of differentially expressedgenes of R. rickettsii in tick SG, including tRNA synthetases encoding genes. On the contrary, blood-feedingdownregulated most of differentially expressed genes in both organs, but induced type IV secretion systemcomponents and OmpB in tick MG. The combined effects of both stimuli resulted in a merged gene expressionprofile representing features of each stimulus analyzed independently, but was more similar to the profileinduced by blood-feeding.
Conclusion: The upregulation of the majority of differentially expressed genes in tick SG by temperature upshiftsuggests that this stimulus is important to prepare R. rickettsii for transmission to the vertebrate host. Blood-feeding, onthe other hand, induced important virulence genes in the tick MG, which might be associated with colonization of thetick and transmission to the vertebrate host. The role of the proteins identified in this study must be addressed andmight help to define future targets to block tick infection, thereby preventing RMSF. To our knowledge, this is the firsttranscriptional tissue-specific study of a virulent strain of R. rickettsii infecting a natural tick vector.
Virulence genes of Rickettsia rickettsii are differentially modulated by either temperature upshift or blood-feeding in tick midgut and salivary glands
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Minimally Symptomatic Infection in an Ebola ‘Hotspot’: A Cross-Sectional Serosurvey
'Some of the “true negatives” used for the validation of our ELISA assays could have been infected with EBOV'
By using ELISA to measure Zaire Ebola virus antibody concentrations, we identified a significant number of individuals with previously undetected EBOV infection in a ‘hotspot’ village in Sierra Leone, approximately one year after the village outbreak. The findings provide further evidence that Ebola, like many other viral infections, presents with a spectrum of clinical manifestations, including minimally symptomatic infection. These data also suggest that a significant portion of Ebola transmission events may have gone undetected during the outbreak. Further studies are needed to understand the potential risk of transmission and clinical sequelae in individuals with previously undetected EBOV infection.
The phenomenon of previously undetected, minimally symptomatic EBOV infection was evident around the discovery of the virus in 1976. Using an immunofluorescence assay, the World Health Organization/International Study Team found that 19% of contacts of EVD cases—very few of whom gave any history of illness—had antibodies to the virus [15]. In 2000, Leroy and colleagues published a study (based on ELISA/Western blot) and found that of 24 asymptomatic close contacts of Gabonese patients with EVD, 11 developed both IgM and IgG responses to Ebola Zaire antigens, indicating viral infection [16]. Other investigators have found evidence of seropositive individuals in areas without large outbreaks using ELISA and postulate that there may have been active circulation of filovirus without apparent clinical manifestations [17,18]. Heffernan and colleagues also used ELISA in Gabon and found that 1% of individuals in an epidemic zone had IgG antibodies to Ebola Zaire virus, yet no history of exposure [19]. In another study in Gabon, Becquart and colleagues found a 15.3% Ebola Zaire IgG seroprevalence in 220 randomly selected villages and concluded that most of the seropositive persons identified “probably had mild or asymptomatic infection” [20]; however, they used uninfected individuals in France as negative controls. We found that unexposed expatriates (not included as negative controls) had a significantly lower mean log anti-GP (M = 5.25 U/mL, SD = 0.54, N = 12) than unexposed Sierra Leoneans (M = 6.40 U/mL, SD = 1.06, N = 132) using the two-sample t-test for unequal variances, t(20.05) = 6.40, P< = 0.001 (see Fig 3), potentially due to cross-reactivity of our assay with closely related pathogens circulating in the region.
Our study has several possible limitations. First, if asymptomatic EBOV infection is a common occurrence, it is possible that some of the “true negatives” used for the validation of our ELISA assays could have been infected with EBOV
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Molecular aspects of MERS-CoV
Middle East respiratory syndrome coronavirus (MERS-CoV) is a betacoronavirus which can cause acute respiratory distress in humans and is associated with a relatively high mortality rate. Since it was first identified in a patient who died in a Jeddah hospital in 2012, the World Health Organization has been notified of 1735 laboratory-confirmed cases from 27 countries, including 628 deaths. Most cases have occurred in Saudi Arabia. MERS-CoV ancestors may be found in Old World bats of the Vespertilionidae family. After a proposed bat to camel switching event, transmission of MERS-CoV to humans is likely to have been the result of multiple zoonotic transfers from dromedary camels. Human-to-human transmission appears to require close contact with infected persons, with outbreaks mainly occurring in hospital environments. Outbreaks have been associated with inadequate infection prevention and control implementation, resulting in recommendations on basic and more advanced infection prevention and control measures by the World Health Organization, and issuing of government guidelines based on these recommendations in affected countries including Saudi Arabia. Evolutionary changes in the virus, particularly in the viral spike protein which mediates virus-host cell contact may potentially increase transmission of this virus. Efforts are on-going to identify specific evidence-based therapies or vaccines. The broad-spectrum antiviral nitazoxanide has been shown to have in vitro activity against MERS-CoV. Synthetic peptides and candidate vaccines based on regions of the spike protein have shown promise in rodent and non-human primate models. GLS-5300, a prophylactic DNA-plasmid vaccine encoding S protein, is the first MERS-CoV vaccine to be tested in humans, while monoclonal antibody, m336 has given promising results in animal models and has potential for use in outbreak situations.
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Spatiotemporal Fluctuations and Triggers of Ebola Virus Spillover
Because the natural reservoir of Ebola virus remains unclear and disease outbreaks in humans have occurred only sporadically over a large region, forecasting when and where Ebola spillovers are most likely to occur constitutes a continuing and urgent public health challenge. We developed a statistical modeling approach that associates 37 human or great ape Ebola spillovers since 1982 with spatiotemporally dynamic covariates including vegetative cover, human population size, and absolute and relative rainfall over 3 decades across sub-Saharan Africa. Our model (area under the curve 0.80 on test data) shows that spillover intensity is highest during transitions between wet and dry seasons;(emph mine, RJS) overall, high seasonal intensity occurs over much of tropical Africa; and spillover intensity is greatest at high (>1,000/km2) and very low (<100/km2) human population densities compared with intermediate levels. These results suggest strong seasonality in Ebola spillover from wild reservoirs and indicate particular times and regions for targeted surveillance.
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Serologic Cross-Reactivity of Human IgM and IgG
Antibodies to Five Species of Ebola Virus
Five species of Ebola virus (EBOV) have been identified, with nucleotide differences of 30–45% between species. Four of
these species have been shown to cause Ebola hemorrhagic fever (EHF) in humans and a fifth species (Reston ebolavirus) is
capable of causing a similar disease in non-human primates. While examining potential serologic cross-reactivity between
EBOV species is important for diagnostic assays as well as putative vaccines, the nature of cross-reactive antibodies
following EBOV infection has not been thoroughly characterized. In order to examine cross-reactivity of human serologic
responses to EBOV, we developed antigen preparations for all five EBOV species, and compared serologic responses by IgM
capture and IgG enzyme-linked immunosorbent assay (ELISA) in groups of convalescent diagnostic sera from outbreaks in
Kikwit, Democratic Republic of Congo (n = 24), Gulu, Uganda (n = 20), Bundibugyo, Uganda (n = 33), and the Philippines
(n = 18), which represent outbreaks due to four different EBOV species. For groups of samples from Kikwit, Gulu, and
Bundibugyo, some limited IgM cross-reactivity was noted between heterologous sera-antigen pairs, however, IgM
responses were largely stronger against autologous antigen. In some instances IgG responses were higher to autologous
antigen than heterologous antigen, however, in contrast to IgM responses, we observed strong cross-reactive IgG antibody
responses to heterologous antigens among all sets of samples. Finally, we examined autologous IgM and IgG antibody
levels, relative to time following EHF onset, and observed early peaking and declining IgM antibody levels (by 80 days) and
early development and persistence of IgG antibodies among all samples, implying a consistent pattern of antibody kinetics,
regardless of EBOV species. Our findings demonstrate limited cross-reactivity of IgM antibodies to EBOV, however, the
stronger tendency for cross-reactive IgG antibody responses can largely circumvent limitations in the utility of heterologous
antigen for diagnostic assays and may assist in the development of antibody-mediated vaccines to EBOV
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