Mosquito feeding behaviour determines the degree of vector-host contact and may have a serious impact on the risk of West Nile virus (WNV) epidemics. Feeding behaviour also interacts with other biotic and abiotic factors that affect virus amplification and transmission.
The occurrence of dengue haemorrhagic fever (DHF) is thought to result from a complex interplay between the virus, host genetics and host immune factors. Existing published data are not consistent, in part related to relatively small sample sizes. We set out to determine possible associations between dengue virus (DEN-V) NS3 specific T cells and cytokine and chemokine levels and the pathogenesis of severe disease in a large cohort of individuals with DHF.
BACKGROUND: The genus Flavivirus includes several pathogenic agents that cause severe illness in humans. Re-emergence of West Nile virus in Europe and continuous spread of certain flaviviruses such as dengue, yellow fever and Japanese encephalitis viruses represent a global danger to public health. Therefore, a rapid and accurate molecular method is required for diagnostics and epidemiological surveillance of flaviviruses. METHODS: A Pan-Flavi quantitative RT-PCR assay using a Locked-Nucleic Acid probe targeting the flavivirus NS5 gene was developed and optimized to detect a wide range of flaviviruses simultaneously. The specificity and sensitivity of the Pan-Flavi assay were tested using RNA of different flaviviruses and non-flaviviruses. Furthermore, the assay was compared directly to flavivirus species-specific assays for the ability to detect flaviviruses sensitively. RESULTS: Two degenerate primers and one Locked-Nucleic Acids probe were designed to amplify most of the flaviviruses. To increase the specificity and fluorescence signal of the Pan-Flavi assay for detection of yellow fever virus and dengue virus 4, additional primers and probes were included. Viral RNA of thirty different flaviviruses was detected, verifying the broad range specificity. The testing of this assay was successful, using standard plasmid and RNA dilutions of yellow fever virus vaccine strain, dengue virus 1 and tick-borne encephalitis virus, with a sensitivity limit of 10–100 genome copies/reaction. Also comparatively good results were achieved for detecting different flaviviruses by the Pan-Flavi assay when compared to the flavivirus species-specific assays. CONCLUSION: The assay is rapid, broad-range flavivirus-specific and highly sensitive making it a valuable tool for rapid detection of flaviviruses in livestock samples, epidemiological studies or as useful complement to single flavivirus-specific assays for clinical diagnosis.
The outbreak of West Nile virus (WNV) in 1999 in the USA, and its continued spread throughout the Americas, parts of Europe, the Middle East and Africa, underscored the need for WNV antiviral development. Here, we review the current status of WNV drug discovery. A number of approaches have been used to search for inhibitors of WNV, including viral infection-based screening, enzyme-based screening, structure-based virtual screening, structure-based rationale design, and antibody-based therapy. These efforts have yielded inhibitors of viral or cellular factors that are critical for viral replication. For small molecule inhibitors, no promising preclinical candidate has been developed; most of the inhibitors could not even be advanced to the stage of hit-to-lead optimization due to their poor drug-like properties. However, several inhibitors developed for related members of the family Flaviviridae, such as dengue virus and hepatitis C virus, exhibited cross-inhibition of WNV, suggesting the possibility to re-purpose these antivirals for WNV treatment. Most promisingly, therapeutic antibodies have shown excellent efficacy in mouse model; one of such antibodies has been advanced into clinical trial. The knowledge accumulated during the past fifteen years has provided better rationale for the ongoing WNV and other flavivirus antiviral development.
Zika virus has emerged as a severe health threat with a rapidly expanding range. The IFITM family of restriction factors inhibits the replication of a broad range of viruses, including the closely related flaviruses West Nile virus and dengue virus. Here, we show that IFITM1 and IFITM3 inhibit Zika virus infection early in the viral life cycle. Moreover, IFITM3 can prevent Zika-virus-induced cell death. These results suggest that strategies to boost the actions and/or levels of the IFITMs might be useful for inhibiting a broad range of emerging viruses.
Sierra Leone in West Africa is in a Lassa fever-hyperendemic region that also includes Guinea and Liberia. Each year, suspected Lassa fever cases result in submission of ≈500-700 samples to the Kenema Government Hospital Lassa Diagnostic Laboratory in eastern Sierra Leone. Generally only 30%-40% of samples tested are positive for Lassa virus (LASV) antigen and/or LASV-specific IgM; thus, 60%-70% of these patients have acute diseases of unknown origin. To investigate what other arthropod-borne and hemorrhagic fever viral diseases might cause serious illness in this region and mimic Lassa fever, we tested patient serum samples that were negative for malaria parasites and LASV. Using IgM-capture ELISAs, we evaluated samples for antibodies to arthropod-borne and other hemorrhagic fever viruses. Approximately 25% of LASV-negative patients had IgM to dengue, West Nile, yellow fever, Rift Valley fever, chikungunya, Ebola, and Marburg viruses but not to Crimean-Congo hemorrhagic fever virus.
The recent rapid spread of Zika virus and its unexpected linkage to birth defects and an autoimmune-neurological syndrome has generated worldwide concern. Zika virus is a flavivirus like dengue, yellow fever and West Nile viruses. We present the 3.8Å resolution structure of mature Zika virus determined by cryo-electron microscopy. The structure of Zika virus is similar to other known flavivirus structures except for the ~10 amino acids that surround the Asn154 glycosylation site found in each of the 180 envelope glycoproteins that make up the icosahedral shell. The carbohydrate moiety associated with this residue, recognizable in the cryo-EM electron density, may function as an attachment site of the virus to host cells. This region varies not only among Zika virus strains but also in other flaviviruses and suggests that changes in this region influence virus transmission and disease.
The most advanced candidate vaccine against dengue viruses, called CYD-TDV, is progressing toward potential registration and review by the World Health Organization (WHO) in 2016. CYD-TDV is a formulation of four chimeric yellow fever 17D vaccine viruses, each one engineered to express the surface envelope and prM (membrane) proteins from one of the four serotypes of dengue virus. The surface envelope protein is a target of virus-neutralizing antibodies. The safety and efficacy of CYD-TDV after the administration of three doses over a 12-month period was recently measured in two pediatric phase 3 trials in Latin America(1) and Southeast Asia.(2) The . . .
AXL-dependent infection of human fetal endothelial cells distinguishes Zika virus from other pathogenic flaviviruses
- Proceedings of the National Academy of Sciences of the United States of America
- Published over 1 year ago
Although a causal relationship between Zika virus (ZIKV) and microcephaly has been established, it remains unclear why ZIKV, but not other pathogenic flaviviruses, causes congenital defects. Here we show that when viruses are produced in mammalian cells, ZIKV, but not the closely related dengue virus (DENV) or West Nile virus (WNV), can efficiently infect key placental barrier cells that directly contact the fetal bloodstream. We show that AXL, a receptor tyrosine kinase, is the primary ZIKV entry cofactor on human umbilical vein endothelial cells (HUVECs), and that ZIKV uses AXL with much greater efficiency than does DENV or WNV. Consistent with this observation, only ZIKV, but not WNV or DENV, bound the AXL ligand Gas6. In comparison, when DENV and WNV were produced in insect cells, they also infected HUVECs in an AXL-dependent manner. Our data suggest that ZIKV, when produced from mammalian cells, infects fetal endothelial cells much more efficiently than other pathogenic flaviviruses because it binds Gas6 more avidly, which in turn facilitates its interaction with AXL.
Background Patients chronically infected with hepatitis C virus (HCV) genotype 2 or 3 for whom treatment with peginterferon is not an option, or who have not had a response to prior interferon treatment, currently have no approved treatment options. In phase 2 trials, regimens including the oral nucleotide polymerase inhibitor sofosbuvir have shown efficacy in patients with HCV genotype 2 or 3 infection. Methods We conducted two randomized, phase 3 studies involving patients with chronic HCV genotype 2 or 3 infection. In one trial, patients for whom treatment with peginterferon was not an option received oral sofosbuvir and ribavirin (207 patients) or matching placebo (71) for 12 weeks. In a second trial, patients who had not had a response to prior interferon therapy received sofosbuvir and ribavirin for 12 weeks (103 patients) or 16 weeks (98). The primary end point was a sustained virologic response at 12 weeks after therapy. Results Among patients for whom treatment with peginterferon was not an option, the rate of a sustained virologic response was 78% (95% confidence interval [CI], 72 to 83) with sofosbuvir and ribavirin, as compared with 0% with placebo (P<0.001). Among previously treated patients, the rate of response was 50% with 12 weeks of treatment, as compared with 73% with 16 weeks of treatment (difference, -23 percentage points; 95% CI, -35 to -11; P<0.001). In both studies, response rates were lower among patients with genotype 3 infection than among those with genotype 2 infection and, among patients with genotype 3 infection, lower among those with cirrhosis than among those without cirrhosis. The most common adverse events were headache, fatigue, nausea, and insomnia; the overall rate of discontinuation of sofosbuvir was low (1 to 2%). Conclusions In patients with HCV genotype 2 or 3 infection for whom treatment with peginterferon and ribavirin was not an option, 12 or 16 weeks of treatment with sofosbuvir and ribavirin was effective. Efficacy was increased among patients with HCV genotype 2 infection and those without cirrhosis. In previously treated patients with genotype 3 infection, 16 weeks of therapy was significantly more effective than 12 weeks. (Funded by Gilead Sciences; POSITRON and FUSION ClinicalTrials.gov numbers, NCT01542788 and NCT01604850 , respectively.).