The reemergence of yellow fever Barrett, Alan D T
Science (American Association for the Advancement of Science),
08/2018, Letnik:
361, Številka:
6405
Journal Article
Recenzirano
Since 2016, yellow fever has become a major public health concern.
A resurgence of yellow fever disease in multiple African countries has proved difficult to control. Given that we have a highly effective vaccine that confers lifelong immunity, why is yellow fever ...still a problem? Much of the answer lies in vaccine supply and demand.
Yellow fever, caused by yellow fever virus, is a mosquito-borne flavivirus disease; it is found in sub-Saharan Africa and tropical South America, where approximately 1 billion people in 46 countries are at risk for it. A live attenuated vaccine (strain 17D) was developed by Max Theiler and colleagues in the 1930s — work that earned Theiler a Nobel Prize. An excellent vaccine, it has been in use since 1937; more than 650 million doses have been distributed in the past 75 years, and 1 dose probably confers lifelong protective immunity. The disease, however, has not been conquered: there are still . . .
Abstract Yellow fever (YF) is regarded as the original hemorrhagic fever and has been a major public health problem for at least 250 years. A very effective live attenuated vaccine, strain 17D, was ...developed in the 1930s and this has proved critical in the control of the disease. There is little doubt that without the vaccine, YF virus would be considered a biosafety level 4 pathogen. Significantly, YF is currently the only disease where an international vaccination certificate is required under the International Health Regulations. Despite having a very successful vaccine, there are occasional issues of supply and demand, such as that which occurred in Angola and Democratic Republic of Congo in 2016 when there was insufficient vaccine available. For the first time fractional dosing of the vaccine was approved on an emergency basis. Thus, continued vigilance and improvements in supply and demand are needed in the future.
Many pandemics have been attributed to the ability of some RNA viruses to change their host range to include humans. Here, we review the mechanisms of disease emergence that are related to the ...host-range specificity of selected mosquito-borne alphaviruses and flaviviruses. We discuss viruses of medical importance, including Venezuelan equine and Japanese encephalitis viruses, dengue viruses and West Nile viruses.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Yellow fever virus (YFV) remains the cause of severe morbidity and mortality in South America and Africa. To determine the evolutionary history of this important reemerging pathogen, we performed a ...phylogenetic analysis of the largest YFV data set compiled to date, representing the prM/E gene region from 133 viral isolates sampled from 22 countries over a period of 76 years. We estimate that the currently circulating strains of YFV arose in Africa within the last 1,500 years and emerged in the Americas following the slave trade approximately 300-400 years ago. These viruses then spread westwards across the continent and persist there to this day in the jungles of South America. We therefore illustrate how gene sequence data can be used to test hypotheses of viral dispersal and demographics, and document the role of human migration in the spread of infectious disease.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Asian lineage of Zika virus (ZIKV) has recently caused epidemics and severe disease. Unraveling the mechanisms causing increased viral transmissibility and disease severity requires experimental ...systems. We report an infectious cDNA clone of ZIKV that was generated using a clinical isolate of the Asian lineage. The cDNA clone-derived RNA is infectious in cells, generating recombinant ZIKV. The recombinant virus is virulent in established ZIKV mouse models, leading to neurological signs relevant to human disease. Additionally, recombinant ZIKV is infectious for Aedes aegypti and thus provides a means to examine virus transmission. The infectious cDNA clone was further used to generate a luciferase ZIKV that exhibited sensitivity to a panflavivirus inhibitor, highlighting its potential utility for antiviral screening. This ZIKV reverse genetic system, together with mouse and mosquito infection models, may help identify viral determinants of human virulence and mosquito transmission as well as inform vaccine and therapeutic strategies.
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•An infectious cDNA clone of Zika virus and a luciferase reporter virus were developed•Recombinant Zika virus is virulent in A129 and AG129 mice•Recombinant Zika virus is highly infectious for Aedes aegypti mosquitos•The luciferase Zika virus can be used for antiviral drug discovery
Zika virus (ZIKV) is causing devastating epidemics with severe disease. Shan et al. generated an infectious cDNA clone of ZIKV as well as a luciferase reporter virus. Recombinant ZIKV is virulent in mice and infectious in Aedes aegypti and thus may help identify viral determinants of virulence and transmission.
Yellow fever virus (YFV) is the prototype member of the genus Flavivirus, a group of viruses that are transmitted between vertebrates by arthropod vectors. The virus is found in tropical regions of ...Africa and South America and is transmitted to primates by mosquitoes: Aedes spp. in Africa and Haemagogus and Sabethes spp. in South America. Despite the availability of an effective vaccine, yellow fever (YF) is considered a reemerging disease owing to its increased incidence in the past 25 years. Molecular epidemiologic data suggest there are seven genotypes of YFV that are geographically separated, and outbreaks of disease are more associated with particular genotypes. In addition, the risk of urban YF, owing to transmission of the virus by Aedes aegypti, is increasing in Africa, as is the potential of urban YF returning to South America. Both present serious potential public health problems to large population centers.
In recent years, genotype I (GI) of Japanese encephalitis virus (JEV) has displaced genotype III (GIII) as the dominant virus genotype throughout Asia. In this study, the largest collection of GIII ...and GI envelope gene-derived viral sequences assembled to date was used to reconstruct the spatiotemporal chronology of genotype displacement throughout Asia and to determine the evolutionary and epidemiological dynamics underlying this significant event. GI consists of two clades, GI-a and GI-b, with the latter being associated with displacement of GIII as the dominant JEV genotype throughout Asia in the 1990s. Phylogeographic analysis indicated that GI-a diverged in Thailand or Cambodia and has remained confined to tropical Asia, whereas GI-b diverged in Vietnam and then dispersed northwards to China, where it was subsequently dispersed to Japan, Korea, and Taiwan. Molecular adaptation was detected by more than one method at one site (residue 15), and coevolution was detected at two pairs of sites (residues 89 to 360 and 129 to 141) within the GI E gene protein alignment. Viral multiplication and temperature sensitivity analyses in avian and mosquito cells revealed that the GI-b isolate JE-91 had significantly higher infectivity titers in mosquito cells from 24 to 48 h postinfection than did the GI-a and GIII isolates. If the JE-91 isolate is indeed representative of GI-b, an increased multiplicative ability of GI-b viruses compared to that of GIII viruses early in mosquito infection may have resulted in a shortened extrinsic incubation period that led to an increased number of GI enzootic transmission cycles and the subsequent displacement of GIII.
Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, represents the most significant etiology of childhood viral neurological infection in Asia. Despite the existence of effective vaccines, JEV is responsible for an estimated 68,000 human cases and a reported 10,000 to 15,000 deaths annually. Phylogenetic studies divided JEV into five geographically and epidemiologically distinct genotypes (GI to GV). GIII has been the source of numerous JEV epidemics throughout history and was the most frequently isolated genotype throughout most of Asia from 1935 until the 1990s. In recent years, GI has displaced GIII as the most frequently isolated virus genotype. To date, the mechanism of this genotype replacement has remained unknown. In this study, we have identified genetic determinants underlying the genotype displacement as it unfolded across Asia. JEV provides a paradigm for other flaviviruses, including West Nile, yellow fever, and dengue viruses, and the critical role of the selective advantages in the mosquito vector.
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