Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 4 de 4
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Infect Genet Evol ; 11(2): 460-8, 2011 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-21215334

RESUMO

St. Louis encephalitis virus (SLEV; Flaviviridae; Flavivirus) is a member of the Japanese encephalitis serocomplex and a close relative of West Nile virus (WNV). Although SLEV remains endemic to the US, both levels of activity and geographical dispersal are relatively constrained when compared to the widespread distribution of WNV. In recent years, WNV appears to have displaced SLEV in California, yet both viruses currently coexist in Texas and several other states. It has become clear that viral swarm characterization is required if we are to fully evaluate the relationship between viral genomes, viral evolution, and epidemiology. Mutant swarm size and composition may be particularly important for arboviruses, which require replication not only in diverse tissues but also divergent hosts. In order to evaluate temporal, spatial, and host-specific patterns in the SLEV mutant swarm, we determined the size, composition, and phylogeny of the intrahost swarm within primary mosquito isolates from both Texas and California. Results indicate a general trend of decreasing intrahost diversity over time in both locations, with recent isolates being highly genetically homogeneous. Additionally, phylogenic analyses provide detailed information on the relatedness of minority variants both within and among strains and demonstrate how both geographic isolation and seasonal maintenance have shaped the viral swarm. Overall, these data generally provide insight into how time, space, and unique transmission cycles influence the SLEV mutant swarm and how understanding these processes can ultimately lead to a better understanding of arbovirus evolution and epidemiology.


Assuntos
Culex/virologia , Vírus da Encefalite de St. Louis/genética , Vírus da Encefalite de St. Louis/isolamento & purificação , Especificidade de Hospedeiro , Insetos Vetores/virologia , Mutação , Animais , Aves/virologia , California/epidemiologia , Encefalite de St. Louis/epidemiologia , Encefalite de St. Louis/transmissão , Encefalite de St. Louis/virologia , Variação Genética , Genoma Viral , Humanos , Filogenia , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Homologia de Sequência , Texas/epidemiologia
2.
PLoS One ; 4(11): e7876, 2009 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-19924238

RESUMO

St. Louis encephalitis virus (SLEV; Flaviviridae, flavivirus) was the major cause of epidemic flaviviral encephalitis in the U.S. prior to the introduction of West Nile virus (WNV) in 1999. However, outbreaks of SLEV have been significantly more limited then WNV in terms of levels of activity and geographic dispersal. One possible explanation for these variable levels of activity is that differences in the potential for each virus to adapt to its host cycle exist. The need for arboviruses to replicate in disparate hosts is thought to result in constraints on both evolution and host-specific adaptation. If cycling is the cause of genetic stability observed in nature and arboviruses lack host specialization, then sequential passage should result in both the accumulation of mutations and specialized viruses better suited for replication in that host. Previous studies suggest that WNV and SLEV differ in capacity for both genetic change and host specialization, and in the costs each accrues from specializing. In an attempt to clarify how selective pressures contribute to epidemiological patterns of WNV and SLEV, we evaluated mutant spectra size, consensus genetic change, and phenotypic changes for SLEV in vivo following 20 sequential passages via inoculation in either Culex pipiens mosquitoes or chickens. Results demonstrate that the capacity for genetic change is large for SLEV and that the size of the mutant spectrum is host-dependent using our passage methodology. Despite this, a general lack of consensus change resulted from passage in either host, a result that contrasts with the idea that constraints on evolution in nature result from host cycling alone. Results also suggest that a high level of adaptation to both hosts already exists, despite host cycling. A strain significantly more infectious in chickens did emerge from one lineage of chicken passage, yet other lineages and all mosquito passage strains did not display measurable host-specific fitness gains. In addition, increased infectivity in chickens did not decrease infectivity in mosquitoes, which further contrasts the concept of fitness trade-offs for arboviruses.


Assuntos
Vírus da Encefalite de St. Louis/metabolismo , Encefalite de St. Louis/transmissão , Animais , Evolução Biológica , Galinhas , Chlorocebus aethiops , Clonagem Molecular , Culicidae , Encefalite de St. Louis/veterinária , Feminino , Variação Genética , Concentração Inibidora 50 , Cinética , Análise de Sequência de DNA , Especificidade da Espécie , Células Vero
3.
Am J Trop Med Hyg ; 79(3): 447-51, 2008 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-18784241

RESUMO

Eastern gray squirrels (Sciurus carolinensis) have shown high West Nile virus (WNV) seroprevalence, and WNV infection has been suggested as a cause of morbidity and mortality in this species. We experimentally infected nine eastern gray squirrels with WNV to determine the clinical effects of infection and to assess their potential role as amplifying hosts. We observed no morbidity or mortality attributable to WNV infection, but lesions were apparent in several organs. We detected mean viremias of 10(5.1) and 10(4.8) plaque-forming units (PFU)/mL on days 3 and 4 post-infection (DPI) and estimated that approximately 2.1% of Culex pipiens feeding on squirrels during 1-5 DPI would become infectious. Thus, S. carolinensis are unlikely to be important amplifying hosts and may instead dampen the intensity of transmission in most host communities. The low viremias and lack of mortality observed in S. carolinensis suggest that they may be useful as sentinels of spillover from the enzootic amplification cycle.


Assuntos
Doenças dos Roedores/transmissão , Sciuridae , Febre do Nilo Ocidental/veterinária , Vírus do Nilo Ocidental , Animais , Feminino , Masculino , Doenças dos Roedores/virologia , Viremia , Febre do Nilo Ocidental/transmissão , Febre do Nilo Ocidental/virologia , Vírus do Nilo Ocidental/patogenicidade
4.
J Gen Virol ; 89(Pt 7): 1633-1642, 2008 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-18559933

RESUMO

West Nile virus (WNV), a mosquito-borne flavivirus, has significantly expanded its geographical and host range since its 1999 introduction into North America. The underlying mechanisms of evolution of WNV and other arboviruses are still poorly understood. Studies evaluating virus adaptation and fitness in relevant in vivo systems are largely lacking. In order to evaluate the capacity for host-specific adaptation and the genetic correlates of adaptation in vivo, this study measured phenotypic and genotypic changes in WNV resulting from passage in Culex pipiens mosquitoes. An increase in replicative ability of WNV in C. pipiens was attained for the two lineages of WNV tested. This adaptation for replication in mosquitoes did not result in a replicative cost in chickens, but did decrease cell-to-cell spread of virus in vertebrate cell culture. Genetic analyses of one mosquito-adapted lineage revealed a total of nine consensus nucleotide substitutions with no accumulation of a significant mutant spectrum. These results differed significantly from previous in vitro studies. When St Louis encephalitis virus (SLEV), a closely related flavivirus, was passaged in C. pipiens, moderately attenuated growth in C. pipiens was observed for two lineages tested. These results suggest that significant differences in the capacity for mosquito adaptation may exist between WNV and SLEV, and demonstrate that further comparative studies in relevant in vivo systems will help elucidate the still largely unknown mechanisms of arboviral adaptation in ecologically relevant hosts.


Assuntos
Culex/virologia , Interações Hospedeiro-Patógeno , Vírus do Nilo Ocidental/crescimento & desenvolvimento , Vírus do Nilo Ocidental/genética , Adaptação Biológica , Substituição de Aminoácidos/genética , Animais , Galinhas/virologia , Chlorocebus aethiops , Análise Mutacional de DNA , Evolução Molecular , Mutação de Sentido Incorreto , RNA Viral/genética , Inoculações Seriadas , Células Vero , Ensaio de Placa Viral , Replicação Viral
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...