Abstract The development of infectious cDNA for different alphaviruses opened an opportunity to explore their attenuation by extensively modifying the viral genomes, an approach that might minimize ...or exclude the reversion to the wild-type, pathogenic phenotype. Moreover, the genomes of such alphaviruses can be engineered to contain RNA elements that would be functional only in cells of vertebrate, but not insect, origin. In the present study, we developed a recombinant VEEV that is more attenuated than TC-83 and capable of replicating only in vertebrate cells. This phenotype was achieved by rendering the translation of the viral structural proteins, and ultimately viral replication, dependent on the internal ribosome entry site of encephalomyocarditis virus (EMCV IRES). This recombinant virus was viable, but required additional, adaptive mutations in nsP2 that strongly increased its replication rates. In spite of efficient replication in cultured vertebrate cells, the genetically modified VEEV demonstrated a highly attenuated phenotype in newborn mice, and yet induced protective immunity against VEEV infection.
Background:
Venezuelan equine encephalitis virus (VEEV) is an arbovirus endemic to the Americas, for which no vaccines or antiviral agents have been approved. TC-83 and V3526 are the ...best-characterized vaccine candidates for VEEV. Both are live-attenuated vaccines and have been associated with safety concerns, although fewer concerns exist for V3526. A previous attempt to improve the TC-83 vaccine focused on further attenuating the vaccine by adding mutations that alter the error-incorporation rate of the RNA-dependent RNA polymerase (RdRp).
Methods:
The research herein examined the effects of these RdRp mutations in V3526 by cloning the 3X and 4X strains, assessing vaccine efficacy against challenge in adult female CD-1 mice, examining neutralizing-antibody titers, investigating vaccine tissue tropism, and testing the stability of the mutant strains.
Results:
The V3526 RdRp mutants exhibited less tissue tropism in the spleen and kidney than the wild-type V3526, while maintaining vaccine efficacy. Illumina sequencing indicated that the RdRp mutations reverted to wild-type V3526 after five passages in murine pup brains.
Conclusions:
The observed genotypic reversion is likely to be of limited concern, because wild-type V3526 remains an effective vaccine capable of providing protection. Our results indicate that the V3526 RdRp mutants may be a safer vaccine design than the original V3526.
An unknown virus was isolated from a mosquito pool collected in Jakarta during routine surveillance in 1979. Analysis of the sample using the Illumina platform resulted in the identification of a ...Newcastle disease virus (NDV) isolate. The sequence of the isolate indicated that it is an ancestral lineage of class II, genotype XIII. The source of the isolate is unusual, as newcastle disease virus is not believed to be vector-borne, although this mosquito pool was processed in a laboratory also handling samples for avian influenza surveillance and it is possible that this resulted in cross-contamination. This NDV isolate is still ancestral to most extant genotype XIII strains and provides a useful insight into historic NDV evolution.
To generate the most diverse phylogenetic dataset for the flaviviruses to date, we determined the genomic sequences and phylogenetic relationships of 14 flaviviruses, of which 10 are primarily ...associated with Culex spp. mosquitoes. We analyze these data, in conjunction with a comprehensive collection of flavivirus genomes, to characterize flavivirus evolutionary and biogeographic history in unprecedented detail and breadth. Based on the presumed introduction of yellow fever virus into the Americas via the transatlantic slave trade, we extrapolated a timescale for a relevant subset of flaviviruses whose evolutionary history, shows that different Culex-spp. associated flaviviruses have been introduced from the Old World to the New World on at least five separate occasions, with 2 different sets of factors likely to have contributed to the dispersal of the different viruses. We also discuss the significance of programmed ribosomal frameshifting in a central region of the polyprotein open reading frame in some mosquito-associated flaviviruses.
Host species-specific fitness landscapes largely determine the outcome of host switching during pathogen emergence. Using chikungunya virus (CHIKV) to study adaptation to a mosquito vector, we ...evaluated mutations associated with recently evolved sub-lineages. Multiple Aedes albopictus-adaptive fitness peaks became available after CHIKV acquired an initial adaptive (E1-A226V) substitution, permitting rapid lineage diversification observed in nature. All second-step mutations involved replacements by glutamine or glutamic acid of E2 glycoprotein amino acids in the acid-sensitive region, providing a framework to anticipate additional A. albopictus-adaptive mutations. The combination of second-step adaptive mutations into a single, 'super-adaptive' fitness peak also predicted the future emergence of CHIKV strains with even greater transmission efficiency in some current regions of endemic circulation, followed by their likely global spread.
Many examples of the emergence or re-emergence of infectious diseases involve the adaptation of zoonotic viruses to new amplification hosts or to humans themselves. These include several instances of ...simple mutational adaptations, often to hosts closely related to the natural reservoirs. However, based on theoretical grounds, arthropod-borne viruses, or arboviruses, may face several challenges for adaptation to new hosts. Here, we review recent findings regarding adaptive evolution of arboviruses and its impact on disease emergence. We focus on the zoonotic alphaviruses Venezuelan equine encephalitis and chikungunya viruses, which have undergone adaptive evolution that mediated recent outbreaks of disease, as well as the flaviviruses dengue and West Nile viruses, which have emerged via less dramatic adaptive mechanisms.
Coues rice rat (Oryzomys couesi), a species abundant throughout Central America, was evaluated experimentally for the ability to serve as an amplifying host for three arboviruses: Patois ...(Bunyaviridae, Orthobunyavirus), Nepuyo (Orthobunyavirus), and Venezuelan equine encephalitis virus subtype ID (Togaviridae, Alphavirus). These three viruses have similar ecologies and are known to co-circulate in nature. Animals from all three cohorts survived infection and developed viremia with no apparent signs of illness and long-lasting antibodies. Thus, O. couesi may play a role in the general maintenance of these viruses in nature.
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