Levels of Angiopoietin 2 Are Predictive for Mortality in Patients Infected With Yellow Fever Virus.

In 2018 there was a large yellow fever outbreak in São Paulo, Brazil, with a high fatality rate. Yellow fever virus can cause, among other symptoms, hemorrhage and disseminated intravascular coagulation, indicating a role for endothelial cells in disease pathogenesis. Here, we conducted a case-control study and measured markers related to endothelial damage in plasma and its association with mortality. We found that angiopoietin 2 is strongly associated with a fatal outcome and could serve as a predictive marker for mortality. This could be used to monitor severe cases and provide care to improve disease outcome.

Circulation of yellow fever virus in Benin city, Edo state Nigeria.

Yellow fever (YF) is one of the most acute viral hemorrhagic diseases of the 18th and 19th centuries, which continues to cause severe morbidity and mortality in Africa. After 21 years of no reported cases of yellow fever in Nigeria, till 2017 where a case was confirmed in Kwara State, also in November 2018,WHO was informed of a cluster of suspected yellow fever cases and deaths in Edo state, Nigeria. The study was among all age group attending health centres in Benin City, Edo state. A total of 280 blood samples were collected from consented febrile patients and were screened for antibodies to Zika virus using rapid diagnostic test (RDT) kits. Blood samples positive to Zika virus (IgM/IgG RDT), were subjected to molecular characterization. Using the flavividae family primers, six (6) samples where confirmed positive by Hemi-nested reverse transcription PCR (hnRT-PCR) sequencing. Nucleotide sequence blast revealed the sequenceswere similar to Yellow fever virus strains. Phylogenetic analysis revealed that the yellow fever virus sequences are closely related to the African strains. Despite the safe and effective yellow fever vaccine, yellow fever virus is seen to be in circulation, hence the need for continues mass vaccination.

Ultrasound Findings and Laboratory Predictors of Early Mortality in Patients With Severe Yellow Fever.

OBJECTIVE. Yellow fever is a hemorrhagic disease caused by an arbovirus endemic in South America; outbreaks have occurred in recent years. The purpose of this study was to describe abdominal ultrasound findings in patients with severe yellow fever and correlate them with clinical and laboratory data. MATERIALS AND METHODS. A retrospective cohort study was performed between January and April 2018. The subjects were patients admitted to an ICU with polymerase chain reaction-confirmed yellow fever. Bedside sonography was performed within 48 hours of admission. Images were independently analyzed by two board-certified radiologists. Laboratory test samples were collected within 12 hours of image acquisition. Multivariable logistic regression analysis was performed to identify 30-day mortality predictors; p < .05 was considered statistically significant. RESULTS. Forty-six patients (40 [87%] men, six [13%] women; mean age, 47.5 ± 15.2 years) were evaluated with bedside sonography. Laboratory tests showed high serum levels of aspartate aminotransferase (5319 U/L), total bilirubin (6.2 mg/dL), and creati-nine (4.3 mg/dL). Twenty-six (56.5%) patients died within 30 days of admission (median time to death, 5 days [interquartile range, 2-9 days]). The most frequent ultrasound findings were gallbladder wall thickening (80.4%), increased renal cortex echogenicity (71.7%), increased liver parenchyma echogenicity (65.2%), perirenal fluid (52.2%), and ascites (30.4%). Increased renal echogenicity was associated with 30-day mortality (84.6% versus 55.0%; p = .046) and was an independent predictor of this outcome after multivariate analysis (odds ratio, 10.89; p = .048). CONCLUSION. Reproducible abdominal ultrasound findings in patients with severe yellow fever may be associated with severity of disease and prognosis among patients treated in the ICU.

Lipase and factor V (but not viral load) are prognostic factors for the evolution of severe yellow fever cases.

BACKGROUND: Despite a highly efficacious vaccine, yellow fever (YF) is still a major threat in developing countries and a cause of outbreaks. In 2018, the Brazilian state of São Paulo witnessed a new YF outbreak in areas where the virus has not been detected before. OBJECTIVE: The aim is to describe the clinical and laboratorial characteristics of severe cases of YF, evaluate viral to determine markers associated with fatal outcome. METHODS: Acute severe YF cases (n = 62) were admitted to the Intensive Care Unit of a reference hospital and submitted to routine laboratorial evaluation on admission. YFV-RNA was detected in serum and urine by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and then sequenced. Patients were classified in two groups: survival or death. FINDINGS: In the univariate analysis the following variables were associated with outcome: alanin aminotransferase (ALT), aspartat aminotransferase (AST), AST/ALT ratio, total bilirubin (TB), chronic kidney disease epidemiology collaboration (CKD-EPI), ammonia, lipase, factor V, international normalised ratio (INR), lactate and bicarbonate. Logistic regression model showed two independent variables associated with death: lipase [odds ratio (OR) 1.018, 95% confidence interval (CI) 1.007 to 1.030, p = 0.002], and factor V (OR -0.955, 95% CI 0.929 to 0.982, p = 0.001). The estimated lipase and factor V cut-off values that maximised sensitivity and specificity for death prediction were 147.5 U/L [area under the curve (AUC) = 0.879], and 56.5% (AUC = 0.913). MAIN CONCLUSIONS: YF acute severe cases show a generalised involvement of different organs (liver, spleen, heart, kidneys, intestines and pancreas), and different parameters were related to outcome. Factor V and lipase are independent variables associated with death, reinforcing the importance of hemorrhagic events due to fulminant liver failure and pointing to pancreatitis as a relevant event in the outcome of the disease.

Development and Clinical Evaluation of a Rapid Diagnostic Test for Yellow Fever Non-Structural Protein 1.

A rapid diagnostic test (RDT) kit was developed to detect non-structural protein 1 (NS1) of yellow fever virus (YFV) using monoclonal antibody. NS1 protein was purified from the cultured YFV and used to immunize mice. Monoclonal antibody to NS1 was selected and conjugated with colloidal gold to produce the YFV NS1 RDT kit. The YFV RDTs were evaluated for sensitivity and specificity using positive and negative samples of monkeys from Brazil and negative human blood samples from Korea. Among monoclonal antibodies, clones 3A11 and 3B7 proved most sensitive, and used for YFV RDT kit. Diagnostic accuracy of YFV RDT was fairly high; Sensitivity was 0.0% and specificity was 100% against Dengue viruses type 2 and 3, Zika, Chikungunya and Mayaro viruses. This YFV RDT kit could be employed as a test of choice for point-of-care diagnosis and large scale surveys of YFV infection under clinical or field conditions in endemic areas and on the globe.

Development of a Real-Time Reverse Transcription-PCR Assay for Global Differentiation of Yellow Fever Virus Vaccine-Related Adverse Events from Natural Infections.

Yellow fever (YF) is a reemerging public health threat, with frequent outbreaks prompting large vaccination campaigns in regions of endemicity in Africa and South America. Specific detection of vaccine-related adverse events is resource-intensive, time-consuming, and difficult to achieve during an outbreak. To address this, we have developed a highly transferable rapid yellow fever virus (YFV) vaccine-specific real-time reverse transcription-PCR (RT-PCR) assay that distinguishes vaccine from wild-type lineages. The assay utilizes a specific hydrolysis probe that includes locked nucleic acids to enhance specific discrimination of the YFV17D vaccine strain genome. Promisingly, sensitivity and specificity analyses reveal this assay to be highly specific to vaccine strain(s) when tested on clinical samples and YFV cell culture isolates of global origin. Taken together, our data suggest the utility of this assay for use in laboratories of varied capacity for the identification and differentiation of vaccine-related adverse events from wild-type infections of both African and South American origin.

Yellow fever in a traveller returning from Suriname to the Netherlands, March 2017.

A Dutch traveller returning from Suriname in early March 2017, presented with fever and severe acute liver injury. Yellow fever was diagnosed by (q)RT-PCR and sequencing. During hospital stay, the patient's condition deteriorated and she developed hepatic encephalopathy requiring transfer to the intensive care. Although yellow fever has not been reported in the last four decades in Suriname, vaccination is recommended by the World Health Organization for visitors to this country.

First DFT-supported point of care and novel electrochemical biosensing: Determination of yellow fever NS1 antibody in human plasma.

In our study, we developed a point of care electrochemical biosensing platform based on the functionalized cysteine-positioned gold electrode to diagnose yellow fever disease from human plasma samples. The developed platform underwent characterization through diverse methods encompassing cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and density-functional theory. The capacitive interaction between yellow fever virus non-structural antigen and antibody gave a cathodic signal at approximately -260 mV, and increased in proportion to the amount of non-structural antibody. The created electrochemical biosensor has an ability to detect 96 ag/mL of the yellow fever non-structural antibody with an extensive analytical range varied from 0.1 fg/mL to 1 µg/mL. The interference effects of various substances that could be found in human plasma, and the performance of the method were examined from the point of recovery and relative standard deviation for human plasma samples; hereby, the results confirmed the unprecedented selectivity and accuracy of the proposed method.

Mapping and Validation of Peptides Differentially Recognized by Antibodies from the Serum of Yellow Fever Virus-Infected or 17DD-Vaccinated Patients.

Yellow Fever disease is caused by the Yellow Fever virus (YFV), an arbovirus from the Flaviviridae family. The re-emergence of Yellow Fever (YF) was facilitated by the increasing urbanization of sylvatic areas, the wide distribution of the mosquito vector, and the low percentage of people immunized in the Americas, which caused severe outbreaks in recent years, with a high mortality rate. Therefore, serological approaches capable of discerning antibodies generated from the wild-type (YFV-WT) strain between the vaccinal strain (YFV-17DD) could facilitate vaccine coverage surveillance, enabling the development of strategies to avoid new outbreaks. In this study, peptides were designed and subjected to microarray procedures with sera collected from individuals infected by WT-YFV and 17DD-YFV of YFV during the Brazilian outbreak of YFV in 2017/2018. From 222 screened peptides, around ten could potentially integrate serological approaches aiming to differentiate vaccinated individuals from naturally infected individuals. Among those peptides, one was synthesized and validated through ELISA.

FluoRNT: A robust, efficient assay for the detection of neutralising antibodies against yellow fever virus 17D.

There is an urgent need for better diagnostic and analytical methods for vaccine research and infection control in virology. This has been highlighted by recently emerging viral epidemics and pandemics (Zika, SARS-CoV-2), and recurring viral outbreaks like the yellow fever outbreaks in Angola and the Democratic Republic of Congo (2016) and in Brazil (2016-2018). Current assays to determine neutralising activity against viral infections in sera are costly in time and equipment and suffer from high variability. Therefore, both basic infection research and diagnostic population screenings would benefit from improved methods to determine virus-neutralising activity in patient samples. Here we describe a robust, objective, and scalable Fluorescence Reduction Neutralisation Test (FluoRNT) for yellow fever virus, relying on flow cytometric detection of cells infected with a fluorescent Venus reporter containing variant of the yellow fever vaccine strain 17D (YF-17D-Venus). It accurately measures neutralising antibody titres in human serum samples within as little as 24 h. Samples from 32 vaccinees immunised with YF-17D were tested for neutralising activity by both a conventional focus reduction neutralisation test (FRNT) and FluoRNT. Both types of tests proved to be equally reliable for the detection of neutralising activity, however, FluoRNT is significantly more precise and reproducible with a greater dynamic range than conventional FRNT. The FluoRNT assay protocol is substantially faster, easier to control, and cheaper in per-assay costs. FluoRNT additionally reduces handling time minimising exposure of personnel to patient samples. FluoRNT thus brings a range of desirable features that can accelerate and standardise the measurement of neutralising anti-yellow fever virus antibodies. It could be used in applications ranging from vaccine testing to large cohort studies in systems virology and vaccinology. We also anticipate the potential to translate the methodology and analysis of FluoRNT to other flaviviruses such as West Nile, Dengue and Zika or to RNA viruses more generally.

An evaluation of the diagnostic performance characteristics of the Yellow Fever IgM immunochromatographic rapid diagnostic test kit from SD Biosensor in Ghana.

Yellow fever is endemic in Ghana and outbreaks occur periodically. The prodromal signs due to Yellow Fever Virus (YFV) infection are non-specific, making clinical signs unreliable as the sole criteria for diagnosis. Accurate laboratory confirmation of suspected yellow fever cases is therefore vital in surveillance programs. Reporting of ELISA IgM testing results by laboratories can delay due to late arrival of samples from the collection sites as well as limited availability of ELISA kits. In this study, the diagnostic performance characteristics of a rapid immunochromatographic Standard Q Yellow Fever IgM test kit (SD Biosensor) was evaluated for the rapid diagnosis of Yellow Fever infection in Ghana. A panel of 275 sera, comprising 81 confirmed YFV positives and 194 negatives were re-tested in this study using the Standard Q Yellow Fever IgM test kit. Using the CDC/WHO Yellow Fever IgM capture ELISA as a benchmark, the sensitivity, specificity and accuracy of the Standard Q Yellow Fever test kit were 96.3%, 97.9% and 97.5%, respectively. The false positivity rate was 5.1% and there was no cross-reactivity when the Standard Q Yellow Fever test kit was tested against dengue, malaria and hepatitis B and C positive samples. In addition, inter-reader variability and invalid rate were both zero. The results indicate that the diagnostic performance of the Standard Q Yellow Fever IgM test kit on serum or plasma is comparable to the serum IgM detection by ELISA and can be used as a point of care rapid diagnostic test kit for YFV infection in endemic areas.

Case report: probable transmission of vaccine strain of yellow fever virus to an infant via breast milk.

The 17D yellow fever vaccine is a live-virus vaccine that has been in use since the 1940s. The incidence of encephalitis after yellow fever vaccination among young infants is much higher than among children older than nine months of age. Until recently, avoidance of vaccination by breastfeeding women who have received yellow fever vaccine had been based on theoretical grounds only. We report the probable transmission of vaccine strain of yellow fever virus from a mother to her infant through breastfeeding.

Seroprevalence of Yellow fever, Chikungunya, and Zika virus at a community level in the Gambella Region, South West Ethiopia.

Yellow fever (YF), Chikungunya (CHIK), and Zika(ZIK) are among re-emerging arboviral diseases of major public health concern. Despite the proximity of the Gambella Region to South Sudan where arboviral cases have been recorded repeatedly the current epidemiological situation is unclear in this part of southwest Ethiopia. Therefore, we conducted a community-based seroprevalence survey of YF virus (YFV), CHIK virus (CHIKV), and ZIK virus (ZIKV) infections in two selected districts. A cross-sectional study was conducted in two locations of the Gambella region (Lare and Itang) to investigate the seroprevalence of these viruses' infections. Blood samples were collected from the study participants and screened for IgG antibodies specific to YFV and CHIKV infections using enzyme-linked immunosorbent assays (ELISA). For the detection of ZIKV specific IgG antibodies, Blockade-of-binding ELISA was used. Data were analyzed using the STATA version 13.1 Softwares. A total of 150 individuals (96 males and 54 females, age ranging from 18 to 65 years, mean age ± SD = 35.92 ± 10.99) participated and provided blood samples. Among the 150 samples 135, 90, and 150 were screened for YFV, CHIKV, and ZIKV, respectively. Hence, 2.9% (95% CI: 1.1-7.7%), 15.6% (95% CI: 9.3-24.8%), and 27.3% (95% CI: 20.7-35.3%) of samples tested positive for IgG antibodies to YFV, CHIKV, and ZIKV infections, respectively. Among the individual seropositive for ZIKV, YFV and CHIKV, only six, one and three had a history of residence outside the Gambella region respectively. Agro-pastoral occupation was significantly associated with a higher prevalence of IgG against CHIKV (AOR = 14.17; 95%CI: 2.30, 87.30) and residency in the Lare district (AOR = 11; 95%CI: 3.31, 39.81) was found to be significantly associated with a higher prevalence of IgG against ZIKV. Our findings revealed the occurrence of YFV, CHIKV and ZIKV infections in the study locations.

Serological Protection 5-6 Years Post Vaccination Against Yellow Fever in African Infants Vaccinated in Routine Programmes.

Introduction: Although effective live attenuated yellow fever (YF) vaccines have been available for over 9 decades sporadic outbreaks continue to occur in endemic regions. These may be linked to several factors including epidemiological factors such as vector and intermediate host distribution or vaccine coverage and efficacy. The World Health Organization's research priorities include gathering systematic evidence around the potential need for booster vaccination with YF vaccine whether this follows full or fractional doses in children. Knowledge on the longevity of response to YF vaccine and the implications of this response needs to be consolidated to guide future vaccination policy. Methods: We measured anti-YF IgG by microneutralization assay in a group of 481 African infants who had received YF vaccine as part of routine EPI programmes, to explore serological protection from YF 5-6 years post YF vaccination, as well as the effect of co variates. Findings: Notably, 22.2% of the cohort had undetectable antibody concentrations, with another 7.5% revealing concentrations below the threshold of seropositivity of 0.5 IU/mL. Sex, season, country and time since vaccination did not affect the longevity of antibody concentration or having antibody concentrations above a defined threshold. Conclusion: Roughly 30% of children in this cohort did not demonstrate anti-yellow fever antibody concentrations above the defined threshold of protection, with 20% having no demonstrable antibody. Knowledge on the longevity of response to YF vaccine and the implications needs to be consolidated to guide future vaccination policy.

Community-based sero-prevalence of chikungunya and yellow fever in the South Omo Valley of Southern Ethiopia.

BACKGROUND: Chikungunya (CHIK) and yellow fever (YF) are becoming major public health threats in East African countries including Ethiopia. In Ethiopia, there is no reliable information about the epidemiology of CHIK. This study aimed to assess a community-based sero-prevalence of CHIK and YF in the South Omo Valley, an endemic area for YF. METHODS: Between February and June 2018, blood samples were collected from study participants and screened for IgG antibody against CHIK virus (CHIKV) and YF virus (YFV) infections using ELISA. Data were computerized using Epi Data Software v.3.1 and analyzed using SPSS. RESULTS: A total of 360 participants (51.7% males, age range from 6 to 80, mean age ± SD = 31.95 ± 14.05 years) participated in this study. The overall sero-prevalence of IgG antibody was 43.6% (157/360) against CHIKV, while it was 49.5% (155/313) against YFV. Out of 155 samples which were positive for IgG antibody to YFV, 93 (60.0%) were positive for IgG antibody to CHIKV. Out of 158 samples which were negative for IgG antibody to YFV, 64(40.5%) were positive for IgG antibody to CHIKV. There was a significant positive correlation between IgG antibodies to CHIKV and YFV (sr = 0.82; P<0.01). Residency in the Debub Ari district (AOR = 8.47; 95% CI: 1.50, 47.74) and travel history to sylvatic areas (AOR = 2.21; 95% CI: 1.02, 4.81) were significantly and positively associated with high sero-prevalence of IgG antibody to CHIKV and YFV, respectively. CONCLUSION: High sero-prevalence of IgG antibody to CHIKV shows the circulation of the virus in the present study area. A low sero-prevalence of IgG antibody to YFV in YF vaccine received individuals is highly concerning from a public health point of view as waning of immune response to YFV infection could result in a periodic outbreaks of YF in endemic areas.Nevertheless, the present study has not investigated for possible cross-reactivity of antibody to CHIKV with other alphaviruses like O'nyong-nyong virus and antibody to YFV with other flaviviruses like Dengue fever virus and this warrants further studies in the present study area.

Nanostructured impedimetric lectin-based biosensor for arboviruses detection.

Arboviruses have been emerging as a significant global health problem due to the recurrent epidemics. Arboviruses require the development of new diagnostic devices due to the nonspecific clinical manifestations. Herein, we report a biosensor based on cysteine (Cys), zinc oxide nanoparticles (ZnONp), and Concanavalin A (ConA) lectin to differentiate between arboviruses infections. ConA is capable of interacting with the saccharide components of the viral capsid. In this study, we evaluated the reproducibility, sensitivity, and specificity of the sensor for the virus of Dengue type 2 (DENV2), Zika (ZIKV), Chikungunya (CHIKV), and Yellow fever (YFV). Atomic force microscopy measurements confirmed the electrode surface modification and revealed a heterogeneous topography during the biorecognition process. Cyclic voltammetry (CV) and impedance spectroscopy (EIS) were used to characterize the biosensor. The blockage of the oxidation-reduction process is related to the formation of Cys-ZnONp-ConA system on the electroactive area and its subsequent interaction with viral glycoproteins. The sensor exhibited a linear response to different concentrations of the studied arboviruses. Our study demonstrates that ConA lectin recognizes the structural glycoproteins of the DENV2, ZIKV, CHIKV, and YFV. DENV2 is the most structurally similar to ZIKV. Our results have shown that the impedimetric response correlates with the structural glycoproteins, as follow: DENV2 (18.6 kΩ) > ZIKV (14.6 kΩ) > CHIKV (6.86 kΩ) > YFV (5.98 kΩ). The homologous structural regions contribute to ConA-arboviruses recognition. Our results demonstrate the use of the proposed system for the development of biosensors for arboviruses infections.

Measurement of Cellular Immune Response to Viral Infection and Vaccination.

Combined cellular and humoral host immune response determine the clinical course of a viral infection and effectiveness of vaccination, but currently the cellular immune response cannot be measured on simple blood samples. As functional activity of immune cells is determined by coordinated activity of signaling pathways, we developed mRNA-based JAK-STAT signaling pathway activity assays to quantitatively measure the cellular immune response on Affymetrix expression microarray data of various types of blood samples from virally infected patients (influenza, RSV, dengue, yellow fever, rotavirus) or vaccinated individuals, and to determine vaccine immunogenicity. JAK-STAT1/2 pathway activity was increased in blood samples of patients with viral, but not bacterial, infection and was higher in influenza compared to RSV-infected patients, reflecting known differences in immunogenicity. High JAK-STAT3 pathway activity was associated with more severe RSV infection. In contrast to inactivated influenza virus vaccine, live yellow fever vaccine did induce JAK-STAT1/2 pathway activity in blood samples, indicating superior immunogenicity. Normal (healthy) JAK-STAT1/2 pathway activity was established, enabling assay interpretation without the need for a reference sample. The JAK-STAT pathway assays enable measurement of cellular immune response for prognosis, therapy stratification, vaccine development, and clinical testing.

Clinical evidence for the immunogenicity and immune persistence of vaccination with yellow fever virus strain 17D in Chinese peacekeepers deployed to Africa.

Yellow fever is a serious disease caused by infection with the yellow fever virus (YFV). A live-attenuated YFV vaccine strain, 17D (YFV-17D) is the only virus strain available for the production of the YFV vaccine. This study evaluated the immunogenicity and immune persistence of vaccination with YFV-17D and identified their influencing factors in Chinese peacekeepers deployed to Africa. Serum specimens were collected before and ≥21 days after primary vaccination with YFV-17D in 349 Chinese peacekeepers who were subsequently deployed to Africa for the first time from 2016 to 2017 (population 1). Serum specimens were collected from 1 to 11 years after vaccination with YFV-17D in 2062 returned Chinese peacekeepers who were deployed to Africa from 2005 to 2015 (population 2). We found that YFV-17D exhibited an excellent protective effect in the Chinese peacekeepers deployed to Africa early following vaccination. In the Chinese peacekeepers one year after vaccination, the serum antibody titer against YFV increased with increasing age at vaccination; in those two or more years after vaccination, the serum antibody titer against YFV decreased over years and was similar to but greater than the minimum protective level 11 years after vaccination. The number of peacekeeping missions exhibited an almost negligible influence on the serum antibody titer against YFV. (This study has been registered at International Clinical Trials Registry Platform (http://www.who.int/ictrp/en/) under registration Nos. ChiCTR1800017024.).

Yellow fever: profile of cases and factors associated with death in a hospital in the State of Rio de Janeiro, 2017-2018.

OBJECTIVE: Describe the clinical and epidemiological profile of confirmed cases of yellow fever whose patients were hospitalized in a general hospital for infectious diseases in the State of Rio de Janeiro, Brazil, from March 11, 2017 to June 15, 2018, during a recent outbreak and factors associated with death. METHODS: This is a retrospective observational study with analysis of secondary databases of local epidemiological surveillance system, and complementary data collection from epidemiological investigation records and clinical records. Study variables included demographic, epidemiological, clinical, and laboratory data. A descriptive statistical analysis and a bivariate and multivariate analysis by logistic regression were performed to analyze factors associated with death. RESULTS: Fifty-two patients diagnosed with yellow fever were hospitalized, 86.5% male patients, median age 49.5 years, 40.4% rural workers. The most frequent signs and symptoms were fever (90.4%), jaundice (86.5%), nausea and/or vomiting (69.2%), changes in renal excretion (53.8%), bleeding (50%), and abdominal pain (48.1%), with comorbidity in 38.5% of all cases. The lethality rate was 40.4%. Factors significantly associated with a higher chance of death in the bivariate analysis were: bleeding, changes in renal excretion, and maximum values of direct bilirubin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), urea, and creatinine. In the multivariate analysis by logistic regression, only changes in renal excretion and ALT remained significant predictors of higher chance of death. A threshold effect was also observed for AST. The cutoff points identified as high risk for death were ALT > 4,000 U/L and AST > 6,000 U/L. CONCLUSIONS: This study contributed to the knowledge on the profile of confirmed cases of high severity yellow fever. The main factors associated with death were changes in renal excretion and elevated serum transaminases, especially ALT. High lethality emphasizes the need for early diagnosis and treatment, and the importance of increasing vaccination coverage.

Yellow fever virus is susceptible to sofosbuvir both in vitro and in vivo.

Yellow fever virus (YFV) is a member of the Flaviviridae family. In Brazil, yellow fever (YF) cases have increased dramatically in sylvatic areas neighboring urban zones in the last few years. Because of the high lethality rates associated with infection and absence of any antiviral treatments, it is essential to identify therapeutic options to respond to YFV outbreaks. Repurposing of clinically approved drugs represents the fastest alternative to discover antivirals for public health emergencies. Other Flaviviruses, such as Zika (ZIKV) and dengue (DENV) viruses, are susceptible to sofosbuvir, a clinically approved drug against hepatitis C virus (HCV). Our data showed that sofosbuvir docks onto YFV RNA polymerase using conserved amino acid residues for nucleotide binding. This drug inhibited the replication of both vaccine and wild-type strains of YFV on human hepatoma cells, with EC50 values around 5 µM. Sofosbuvir protected YFV-infected neonatal Swiss mice and adult type I interferon receptor knockout mice (A129-/-) from mortality and weight loss. Because of its safety profile in humans and significant antiviral effects in vitro and in mice, Sofosbuvir may represent a novel therapeutic option for the treatment of YF. Key-words: Yellow fever virus; Yellow fever, antiviral; sofosbuvir.