Human fatal yellow fever. Immunohistochemical detection of viral antigens in the liver, kidney and heart

Understanding yellow fever-associated myocardial injury: an autopsy study

BACKGROUND

Yellow fever (YF) is a viral hemorrhagic fever, endemic in parts of South America and Africa. There is scarce evidence about the pathogenesis of the myocardial injury. The objective of this study is to evaluate the cardiac pathology in fatal cases of YF.

METHODS

This retrospective autopsy study included cases from the São Paulo (Brazil) epidemic of 2017-2019. We reviewed medical records and performed cardiac tissue histopathological evaluation, electron microscopy, immunohistochemical assays, RT-qPCR for YF virus (YFV)-RNA, and proteomics analysis on inflammatory and endothelial biomarkers.

FINDINGS

Seventy-three confirmed YF cases with a median age of 48 (34-60) years were included. We observed myocardial fibrosis in 68 (93.2%) patients; cardiomyocyte hypertrophy in 68 (93.2%); endothelial alterations in 67 (91.8%); fiber necrosis in 50 (68.5%); viral myocarditis in 9 (12.3%); and secondary myocarditis in 5 (6.8%). Four out of five patients with 17DD vaccine-associated viscerotropic disease presented with myocarditis. The cardiac conduction system showed edema, hemorrhages and endothelial fibrinoid necrosis. Immunohistochemistry detected CD68-positive inflammatory interstitial cells and YFV antigens in endothelial and inflammatory cells. YFV-RNA was detected positive in 95.7% of the cardiac samples. The proteomics analysis demonstrated that YF patients had higher levels of multiple inflammatory and endothelial biomarkers in comparison to cardiovascular controls, and higher levels of interferon gamma-induced protein 10 (IP-10) in comparison to sepsis (p = 0.01) and cardiovascular controls (p < 0.001) in Dunn test.

INTERPRETATION

Myocardial injury is frequent in severe YF, due to multifactorial mechanisms, including direct YFV-mediated damage, endothelial cell injury, and inflammatory response, with a possible prominent role for IP-10.

FUNDING

This study was funded by Fundação de Amparo à Pesquisa do Estado de São Paulo, Bill and Melinda Gates Foundation, Conselho Nacional de Desenvolvimento Científico e Tecnológico, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior.

Neglected and Emerging Infections of The Kidney

Individuals, societies, and the environment are affected by neglected and emerging diseases. These diseases result in a variety of severe outcomes, including permanent disabilities, chronic diseases such as chronic kidney disease, and even mortality. Consequences include high health care expenditures, loss of means of support, social stigma, and social exclusion. The burden of these diseases is exacerbated in low- and middle-income countries owing to poverty, inadequate fundamental infrastructure, and the absence of health and social protection systems. The World Health Organization is committed to promoting the following public health strategies to prevent and control neglected tropical diseases: preventive chemotherapy; intensive case management; vector control; provision of safe drinkable water, sanitation, and hygiene; and veterinary public health. In addition, it promotes a One Health strategy, which is a collaborative, multisectoral, and interdisciplinary approach to achieving the greatest health outcomes by recognizing the interdependence of human beings, animals, plants, and their shared environment. This article provides knowledge and strategies for the prevention and treatment of neglected and emerging diseases, with a particular concentration on kidney diseases, as part of a comprehensive approach to One Health.

Experimental Yellow Fever in Squirrel Monkey: Characterization of Liver In Situ Immune Response

Non-human primates contribute to the spread of yellow fever virus (YFV) and the establishment of transmission cycles in endemic areas, such as Brazil. This study aims to investigate virological, histopathological and immunohistochemical findings in livers of squirrel monkeys (Saimiri spp.) infected with the YFV. Viremia occurred 1-30 days post infection (dpi) and the virus showed a predilection for the middle zone (Z2). The livers were jaundiced with subcapsular and hemorrhagic multifocal petechiae. Apoptosis, lytic and coagulative necrosis, steatosis and cellular edema were also observed. The immune response was characterized by the expression of S100, CD11b, CD57, CD4 and CD20; endothelial markers; stress and cell death; pro and anti-inflammatory cytokines, as well as Treg (IL-35) and IL-17 throughout the experimental period. Lesions during the severe phase of the disease were associated with excessive production of apoptotic pro-inflammatory cytokines, such as IFN-γ and TNF-α, released by inflammatory response cells (CD4+ and CD8+ T lymphocytes) and associated with high expression of molecules of adhesion in the inflammatory foci observed in Z2. Immunostaining of the local endothelium in vascular cells and the bile duct was intense, suggesting a fundamental role in liver damage and in the pathogenesis of the disease.

Understanding Sabiá virus infections (Brazilian mammarenavirus)

BACKGROUND

Only two naturally occurring human Sabiá virus (SABV) infections have been reported, and those occurred over 20 years ago.

METHODS

We diagnosed two new cases of SABV infection using metagenomics in patients thought to have severe yellow fever and described new features of histopathological findings.

RESULTS

We characterized clinical manifestations, histopathology and analyzed possible nosocomial transmission. Patients presented with hepatitis, bleeding, neurological alterations and died. We traced twenty-nine hospital contacts and evaluated them clinically and by RT-PCR and neutralizing antibodies. Autopsies uncovered unique features on electron microscopy, such as hepatocyte "pinewood knot" lesions. Although previous reports with similar New-World arenavirus had nosocomial transmission, our data did not find any case in contact tracing.

CONCLUSIONS

Although an apparent by rare, Brazilian mammarenavirus infection is an etiology for acute hemorrhagic fever syndrome. The two fatal cases had peculiar histopathological findings not previously described. The virological diagnosis was possible only by contemporary techniques such as metagenomic assays. We found no subsequent infections when we used serological and molecular tests to evaluate close contacts.

A High-Throughput Yellow Fever Neutralization Assay

Quick and accurate detection of neutralizing antibodies (nAbs) against yellow fever is essential in serodiagnosis during outbreaks for surveillance and to evaluate vaccine efficacy in population-wide studies. All of this requires serological assays that can process a large number of samples in a highly standardized format. Albeit being laborious, time-consuming, and limited in throughput, the classical plaque reduction neutralization test (PRNT) is still considered the gold standard for the detection and quantification of nAbs due to its sensitivity and specificity. Here, we report the development of an alternative fluorescence-based serological assay (SNTFLUO) with an equally high sensitivity and specificity that is fit for high-throughput testing with the potential for automation. Finally, our novel SNTFLUO was cross-validated in several reference laboratories and against international WHO standards, showing its potential to be implemented in clinical use. SNTFLUO assays with similar performance are available for the Japanese encephalitis, Zika, and dengue viruses amenable to differential diagnostics. IMPORTANCE Fast and accurate detection of neutralizing antibodies (nAbs) against yellow fever virus (YFV) is key in yellow fever serodiagnosis, outbreak surveillance, and monitoring of vaccine efficacy. Although classical PRNT remains the gold standard for measuring YFV nAbs, this methodology suffers from inherent limitations such as low throughput and overall high labor intensity. We present a novel fluorescence-based serum neutralization test (SNTFLUO) with equally high sensitivity and specificity that is fit for processing a large number of samples in a highly standardized manner and has the potential to be implemented for clinical use. In addition, we present SNTFLUO assays with similar performance for Japanese encephalitis, Zika, and dengue viruses, opening new avenues for differential diagnostics.

Immunohistochemical diagnosis of human infectious diseases: a review

BACKGROUND

Immunohistochemistry (IHC) using monoclonal and polyclonal antibodies is a useful diagnostic method for detecting pathogen antigens in fixed tissues, complementing the direct diagnosis of infectious diseases by PCR and culture on fresh tissues. It was first implemented in a seminal publication by Albert Coons in 1941.

MAIN BODY

Of 14,198 publications retrieved from the PubMed, Google, Google Scholar and Science Direct databases up to December 2021, 230 were selected for a review of IHC techniques, protocols and results. The methodological evolutions of IHC and its application to the diagnosis of infectious diseases, more specifically lice-borne diseases, sexually transmitted diseases and skin infections, were critically examined. A total of 59 different pathogens have been detected once in 22 different tissues and organs; and yet non-cultured, fastidious and intracellular pathogens accounted for the vast majority of pathogens detected by IHC. Auto-IHC, incorporating patient serum as the primary antibody, applied to diseased heart valves surgically collected from blood culture-negative endocarditis patients, detected unidentified Gram-positive cocci and microorganisms which were subsequently identified as Coxiella burnetii, Bartonella quintana, Bartonella henselae and Tropheryma whipplei. The application of IHC to ancient tissues dated between the ends of the Ptolemaic period to over 70 years ago, have also contributed to paleomicrobiology diagnoses.

CONCLUSION

IHC plays an important role in diagnostic of infectious diseases in tissue samples. Paleo-auto-IHC derived from auto-IHC, is under development for detecting non-identified pathogens from ancient specimens.

Risk Factors for Acute Kidney Injury and Death in Patients Infected With the Yellow Fever Virus During the 2018 Outbreak in São Paulo, Brazil

Introduction

Methods

Results

Conclusion

Yellow Fever as Cause of Death of Titi Monkeys (Callicebus Spp.)

From 2016 to 2018, an epidemic wave of yellow fever (YF) occurred in Brazil, affecting a large number of Platyrrhini monkeys. Titi monkeys (Callicebus spp.) were severely affected yet pathological characterizations are lacking. This study characterized epizootic YF in 43 titi monkeys (Callicebus spp.) with respect to the microscopic lesions in liver, kidney, spleen, heart, brain, and lung, as well as the distribution of immunolabeling for YF virus antigen, and the flaviviral load in the liver. Of 43 titi monkeys examined, 18 (42%) were positive for yellow fever virus (YFV) by immunohistochemistry or reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR). Affected livers had consistent marked panlobular necrotizing hepatitis, lipidosis, and mild inflammation, with intense immunolabeling for YFV mainly in centrilobular hepatocytes (zone 1; P = .05). In the spleen, consistent findings were variable lymphoid depletion (10/11), lymphoid necrosis (lymphocytolysis; 4/11), and immunolabeling for YFV in histiocytic cells (3/16). The main finding in the kidney was multifocal acute necrosis of tubular epithelium (5/7) that was occasionally associated with intracytoplasmic immunolabeling for YFV (6/15). These data indicate that titi monkeys are susceptible to YFV infection, developing severe hepatic lesions and high viral loads, comparable to humans and Alouatta spp. Thus, Callicebus spp. may be reliable sentinels for YF surveillance.

Two Cases of Natural Infection of Dengue-2 Virus in Bats in the Colombian Caribbean

Dengue, a mosquito-borne zoonotic disease, is the most common vector-borne disease in tropical and subtropical areas. In this study, we aim to demonstrate biological evidence of dengue virus infection in bats. A cross-sectional study was carried out in the departments of Cordoba and Sucre, Colombia. A total of 286 bats were captured following the ethical protocols of animal experimentation. The specimens were identified and euthanized using a pharmacological treatment with atropine, acepromazine and sodium pentobarbital. Duplicate samples of brain, heart, lung, spleen, liver, and kidney were collected with one set stored in Trizol and the other stored in 10% buffered formalin for histopathological and immunohistochemical analysis using polyclonal antibodies. Brain samples from lactating mice with an intracranial inoculation of DENV-2 were used as a positive control. As a negative control, lactating mouse brains without inoculation and bats brains negative for RT-PCR were included. Tissue sections from each specimen of bat without conjugate were used as staining control. In a specimen of Carollia perspicillata captured in Ayapel (Cordoba) and Phylostomus discolor captured in San Carlos (Cordoba), dengue virus was detected, and sequences were matched to DENV serotype 2. In bats RT-PCR positive for dengue, lesions compatible with viral infections, and the presence of antigens in tissues were observed. Molecular findings, pathological lesions, and detection of antigens in tissues could demonstrate viral DENV-2 replication and may correspond to natural infection in bats. Additional studies are needed to elucidate the exact role of these species in dengue epidemics.

A Yellow Fever Virus 17D Infection and Disease Mouse Model Used to Evaluate a Chimeric Binjari-Yellow Fever Virus Vaccine

Despite the availability of an effective, live attenuated yellow fever virus (YFV) vaccine (YFV 17D), this flavivirus still causes up to ≈60,000 deaths annually. A number of new approaches are seeking to address vaccine supply issues and improve safety for the immunocompromised vaccine recipients. Herein we describe an adult female IFNAR-/- mouse model of YFV 17D infection and disease that recapitulates many features of infection and disease in humans. We used this model to evaluate a new YFV vaccine that is based on a recently described chimeric Binjari virus (BinJV) vaccine technology. BinJV is an insect-specific flavivirus and the chimeric YFV vaccine (BinJ/YFV-prME) was generated by replacing the prME genes of BinJV with the prME genes of YFV 17D. Such BinJV chimeras retain their ability to replicate to high titers in C6/36 mosquito cells (allowing vaccine production), but are unable to replicate in vertebrate cells. Vaccination with adjuvanted BinJ/YFV-prME induced neutralizing antibodies and protected mice against infection, weight loss and liver pathology after YFV 17D challenge.

Congenital Zika Syndrome and Extra-Central Nervous System Detection of Zika Virus in a Pre-term Newborn in Mexico

BACKGROUND

During pregnancy, the Zika virus (ZIKV) replicates in the placenta and central nervous system (CNS) of infected fetuses; nevertheless, the ability of ZIKV to replicate in other fetal tissues has not been extensively characterized.

METHODS

We researched whether dissemination of congenitally-acquired ZIKV outside the CNS exists by searching for the accumulation of the viral envelope protein, ZIKV ribonucleic acid (RNA), and infectious viral particles in different organs of a deceased newborn with Congenital Zika Syndrome. A real-time qualitative polymerase chain reaction (qPCR) was used to detect ZIKV RNA in the brain, thymus, lungs, kidneys, adrenal glands, spleen, liver, and small intestine. The same tissues were analyzed by indirect immunofluorescence and immunoperoxidase assays using the monoclonal antibody 4G2 to detect ZIKV envelope antigens. Isolation of infectious ZIKV in a cell culture was carried out using brain and kidney samples.

RESULTS

A postmortem, virological analysis of multiple organs, such as the kidneys (epithelial cells in the renal tubules), lungs (bronchial epithelia), thymus (epithelial cells inside the Hassall's corpuscles), and brain (neurons, ependymal cells, and macrophages) revealed the presence of ZIKV RNA and envelope antigens. Other tissues of the deceased newborn tested positive by qPCR for Epstein-Barr virus and human herpesvirus 6, including the brain cortex (Epstein-Barr) and the thymus, kidneys, and adrenal glands (human herpesvirus 6). The kidneys were identified as a significant niche for viral replication, given that infectious particles were successfully isolated from renal tissues.

CONCLUSIONS

Our findings demonstrate the ability of congenitally-acquired ZIKV to produce disseminated infections and the viral tropism towards epithelial cells.

Viral Hemorrhagic Fevers Other than Ebola and Lassa

Viral hemorrhagic fevers represent a group of diseases caused by enveloped RNA viruses. The epidemiology is broadly variable, ranging from geographically localized to more diffuse infections. Viral hemorrhagic fevers are classified as category A bioweapon agents by the Centers for Disease Control and Prevention. Viral hemorrhagic fevers are severe febrile illnesses with hemorrhagic phenomena. Laboratory diagnosis takes place in highly specialized reference laboratories. Treatment is essentially supportive. In this article, we focus the attention on yellow fever and viral hemorrhagic fevers other than Ebola and Lassa virus diseases that have been described elsewhere in this issue.

Ultrasound-guided minimally invasive autopsy as a tool for rapid post-mortem diagnosis in the 2018 Sao Paulo yellow fever epidemic: Correlation with conventional autopsy

Background

New strategies for collecting post-mortem tissue are necessary, particularly in areas with emerging infections. Minimally invasive autopsy (MIA) has been proposed as an alternative to conventional autopsy (CA), with promising results. Previous studies using MIA addressed the cause of death in adults and children in developing countries. However, none of these studies was conducted in areas with an undergoing infectious disease epidemic. We have recently experienced an epidemic of yellow fever (YF) in Brazil. Aiming to provide new information on low-cost post-mortem techniques that could be applied in regions at risk for infectious outbreaks, we tested the efficacy of ultrasound-guided MIA (MIA-US) in the diagnosis of patients who died during the epidemic.

Methodology/principal findings

In this observational study, we performed MIA-US in 20 patients with suspected or confirmed YF and compared the results with those obtained in subsequent CAs. Ultrasound-guided biopsies were used for tissue sampling of liver, kidneys, lungs, spleen, and heart. Liver samples from MIA-US and CA were submitted for RT-PCR and immunohistochemistry for detection of YF virus antigen. Of the 20 patients, 17 had YF diagnosis confirmed after autopsy by histopathological and molecular analysis. There was 100% agreement between MIA-US and CA in determining the cause of death (panlobular hepatitis with hepatic failure) and main disease (yellow fever). Further, MIA-US obtained samples with good quality for molecular studies and for the assessment of the systemic involvement of the disease. Main extrahepatic findings were pulmonary hemorrhage, pneumonia, acute tubular necrosis, and glomerulonephritis. One patient was a 24-year-old, 27-week pregnant woman; MIA-US assessed the placenta and provided adequate placental tissue for analysis.

Conclusions

MIA-US is a reliable tool for rapid post-mortem diagnosis of yellow fever and can be used as an alternative to conventional autopsy in regions at risk for hemorrhagic fever outbreaks with limited resources to perform complete diagnostic autopsy.

Reliable mortality information is of paramount importance to establish sound public health policies. Autopsy is an important tool not only for determining the cause of death, but also for the detection of novel diseases. In the last decades, we have been globally identifying an unprecedented number of emerging infections. Therefore, there is great interest in the development of less invasive and low-cost tools for the accurate post-mortem diagnosis in fatal cases. Minimally invasive autopsy (MIA), conceived as targeting diagnostic biopsies of key organs by needle puncture, has been proposed as an alternative to conventional autopsy (CA) for the determination of cause of death in developing countries. In this research, we tested the efficacy of MIA in the post-mortem diagnosis of 20 patients with suspected or confirmed yellow fever who died during the recent epidemic of yellow fever that occurred in Brazil. There was a perfect agreement between MIA and CA in determining the cause of death (hepatic failure) and main disease (yellow fever) in all patients with confirmed yellow fever. This finding indicates that MIA can be used as an alternative to CA in regions at risk for infectious disease outbreaks with limited resources to perform conventional autopsies.

Severe yellow fever in Brazil: clinical characteristics and management

BACKGROUND

Little is known about clinical characteristics and management of severe yellow fever as previous yellow fever epidemics often occurred in times or areas with little access to intensive care units (ICU). We aim to describe the clinical characteristics of severe yellow fever cases requiring admission to the ICU during the 2018 yellow fever outbreak in São Paulo, Brazil. Furthermore, we report on preliminary lessons learnt regarding clinical management of severe yellow fever.

METHODS

Retrospective descriptive cohort study. Demographic data, laboratory test results on admission, clinical follow-up, and clinical outcomes were evaluated.

RESULTS

From 10 January to 11 March 2018, 79 patients with laboratory confirmed yellow fever were admitted to the ICU in a tertiary hospital in Sao Paolo because of rapid clinical deterioration. On admission, the median AST was 7,000 IU/L, ALT 3,936 IU/L, total bilirubin 5.3 ml/dL, platelet 74 × 103/mm3, INR 2.24 and factor V 37%. Seizures occurred in 24% of patients, even without substantial intracranial hypertension. The high frequency of pancreatitis and rapidly progressive severe metabolic acidosis were notable findings. 73% of patients required renal replacement therapy. The in-hospital fatality rate was 67%. Patients with diabetes mellitus had a higher case fatality rate (CFR) of 80%, while patients without diabetes had a CFR of 65%. Leading causes of death were severe gastrointestinal bleeding, epileptic status, severe metabolic acidosis, necrohemorrhagic pancreatitis, and multi-organ failure.

CONCLUSIONS

Severe yellow fever is associated with a high CFR. The following management lessons were learnt: Anticonvulsant drugs in patients with any symptoms of hepatic encephalopathy or arterial ammonia levels >70 μmol/L was commenced which reduced the frequency of seizures from 28% to 17%. Other new therapy strategies included early institution of plasma exchange. Due to the high frequency of gastric bleeding, therapeutic doses of intravenous proton pump inhibitors should be administered.

Flaviviruses and Kidney Diseases

The genus Flavivirus comprises approximately 73 viruses, which share several common aspects, such as dimension, structure, nucleic acid properties, and shape in electronic microscopy. Global incidence of flavivirus infection increased dramatically over the last decades, causing large outbreaks in several areas of the world. These viruses are expanding from endemic tropical and subtropical areas to previously nonendemic areas, affecting and causing diseases in millions of individuals worldwide and posing a formidable challenge to public health in several countries. The majority of clinically significant flavivirus-associated infections are mosquito borne (arboviruses-acronym for ARthropod-BOrne VIRUSES), such as dengue, yellow fever, Japanese encephalitis, Zika, and West Nile fever. Most diseases caused by flaviviruses are asymptomatic or manifest as self-limited, mild, undifferentiated febrile diseases. In a limited number of cases, these diseases may evolve to severe inflammatory, multisystem diseases, causing high morbidity and mortality. Some flaviviruses have been consistently identified in kidney tissue and urine and have been clinically associated with kidney diseases. In this review, we will provide an overview of the epidemiology, risk factors, kidney pathology, etiopathogenesis, and outcomes of acute and chronic kidney syndromes associated with dengue, yellow fever, Zika, and West Nile virus disease.

Cardiac Involvement by Yellow Fever(from the PROVAR+ Study)

Incidence of Yellow Fever (YF) has increased in Brazil, and cardiac findings such as bradyarrhythmias and conduction abnormalities have been described. We aimed to perform a comprehensive cardiac evaluation of patients with YF, and to assess the association between cardiac involvement and disease severity. Patients hospitalized with YF from February to March 2018 underwent clinical and laboratory evaluation, focused bedside echocardiography (GE Vivid IQ), electrocardiogram and, in case of alterations, 24-hours Holter. Patients were divided into 2 groups according to YF severity. Five patients underwent magnetic resonance imaging and 3 had necropsy. Seventy patients had confirmed YF, 69% with severe form. Mean age was 48 ± 14 years, 63 (90%) were males and 5 (7%) died. Significant electrocardiogram abnormalities were present in 52% of patients with mild/moderate form of YF (G1) and 77% of those with severe form (G2), p = 0.046. Sinus bradycardia was observed in 24% (N = 17): G1 23% versus G2 25%, p = 0.67. Among 32 patients who underwent Holter, 14 (44%) had mean HR <60 beats per minute, being 8 from G2. Echocardiogram revealed left ventricular dysfunction in 4 (6%) patients, from G2. Left ventricular wall thickening with a hyper-refringent myocardial texture suggesting infiltration was observed in 17 patients (G1 18% vs G2 27%, p = 0.55). One magnetic resonance (G2) was suggestive of myocarditis, and one necropsy revealed areas of myocardial necrosis and acute myocarditis. In conclusion, cardiac involvement was observed in patients with YF, most commonly bradycardia and myocardial hyper-refringent texture suggestive of infiltration.

Yellow Fever Virus: Knowledge Gaps Impeding the Fight Against an Old Foe

Yellow fever (YF) was one of the most dangerous infectious diseases of the 18th and 19th centuries, resulting in mass casualties in Africa and the Americas. The etiologic agent is yellow fever virus (YFV), and its live-attenuated form, YFV-17D, remains one of the most potent vaccines ever developed. During the first half of the 20th century, vaccination combined with mosquito control eradicated YFV transmission in urban areas. However, the recent 2016-2018 outbreaks in areas with historically low or no YFV activity have raised serious concerns for an estimated 400-500 million unvaccinated people who now live in at-risk areas. Once a forgotten disease, we highlight here that YF still represents a very real threat to human health and economies. As many gaps remain in our understanding of how YFV interacts with the human host and causes disease, there is an urgent need to address these knowledge gaps and propel YFV research forward.

Acute kidney injury due to tropical infectious diseases and animal venoms: a tale of 2 continents

South and Southeast Asia and Latin American together comprise 46 countries and are home to approximately 40% of the world population. The sociopolitical and economic heterogeneity, tropical climate, and malady transitions characteristic of the region strongly influence disease behavior and health care delivery. Acute kidney injury epidemiology mirrors these inequalities. In addition to hospital-acquired acute kidney injury in tertiary care centers, these countries face a large preventable burden of community-acquired acute kidney injury secondary to tropical infectious diseases or animal venoms, affecting previously healthy young individuals. This article reviews the epidemiology, clinical picture, prevention, risk factors, and pathophysiology of acute kidney injury associated with tropical diseases (malaria, dengue, leptospirosis, scrub typhus, and yellow fever) and animal venom (snakes, bees, caterpillars, spiders, and scorpions) in tropical regions of Asia and Latin America, and discusses the potential future challenges due to emerging issues.

New approaches for the standardization and validation of a real-time qPCR assay using TaqMan probes for quantification of yellow fever virus on clinical samples with high quality parameters

The development and production of viral vaccines, in general, involve several steps that need the monitoring of viral load throughout the entire process. Applying a 2-step quantitative reverse transcription real time PCR assay (RT-qPCR), viral load can be measured and monitored in a few hours. In this context, the development, standardization and validation of a RT-qPCR test to quickly and efficiently quantify yellow fever virus (YFV) in all stages of vaccine production are extremely important. To serve this purpose we used a plasmid construction containing the NS5 region from 17DD YFV to generate the standard curve and to evaluate parameters such as linearity, precision and specificity against other flavivirus. Furthermore, we defined the limits of detection as 25 copies/reaction, and quantification as 100 copies/reaction for the test. To ensure the quality of the method, reference controls were established in order to avoid false negative results. The qRT-PCR technique based on the use of TaqMan probes herein standardized proved to be effective for determining yellow fever viral load both in vivo and in vitro, thus becoming a very important tool to assure the quality control for vaccine production and evaluation of viremia after vaccination or YF disease.

Yellow Fever 17DD Vaccine Virus Infection Causes Detectable Changes in Chicken Embryos

The yellow fever (YF) 17D vaccine is one of the most effective human vaccines ever created. The YF vaccine has been produced since 1937 in embryonated chicken eggs inoculated with the YF 17D virus. Yet, little information is available about the infection mechanism of YF 17DD virus in this biological model. To better understand this mechanism, we infected embryos of Gallus gallus domesticus and analyzed their histopathology after 72 hours of YF infection. Some embryos showed few apoptotic bodies in infected tissues, suggesting mild focal infection processes. Confocal and super-resolution microscopic analysis allowed us to identify as targets of viral infection: skeletal muscle cells, cardiomyocytes, nervous system cells, renal tubular epithelium, lung parenchyma, and fibroblasts associated with connective tissue in the perichondrium and dermis. The virus replication was heaviest in muscle tissues. In all of these specimens, RT-PCR methods confirmed the presence of replicative intermediate and genomic YF RNA. This clearer characterization of cell targets in chicken embryos paves the way for future development of a new YF vaccine based on a new cell culture system.

Surveillance for yellow Fever virus in non-human primates in southern Brazil, 2001-2011: a tool for prioritizing human populations for vaccination

In Brazil, epizootics among New World monkey species may indicate circulation of yellow fever (YF) virus and provide early warning of risk to humans. Between 1999 and 2001, the southern Brazilian state of Rio Grande do Sul initiated surveillance for epizootics of YF in non-human primates to inform vaccination of human populations. Following a YF outbreak, we analyzed epizootic surveillance data and assessed YF vaccine coverage, timeliness of implementation of vaccination in unvaccinated human populations. From October 2008 through June 2009, circulation of YF virus was confirmed in 67 municipalities in Rio Grande do Sul State; vaccination was recommended in 23 (34%) prior to the outbreak and in 16 (24%) within two weeks of first epizootic report. In 28 (42%) municipalities, vaccination began more than two weeks after first epizootic report. Eleven (52%) of 21 laboratory-confirmed human YF cases occurred in two municipalities with delayed vaccination. By 2010, municipalities with confirmed YF epizootics reported higher vaccine coverage than other municipalities that began vaccination. In unvaccinated human populations timely response to epizootic events is critical to prevent human yellow fever cases.

Yellow Fever outbreaks in unvaccinated populations, Brazil, 2008-2009

Due to the risk of severe vaccine-associated adverse events, yellow fever vaccination in Brazil is only recommended in areas considered at risk for disease. From September 2008 through June 2009, two outbreaks of yellow fever in previously unvaccinated populations resulted in 21 confirmed cases with 9 deaths (case-fatality, 43%) in the southern state of Rio Grande do Sul and 28 cases with 11 deaths (39%) in Sao Paulo state. Epizootic deaths of non-human primates were reported before and during the outbreak. Over 5.5 million doses of yellow fever vaccine were administered in the two most affected states. Vaccine-associated adverse events were associated with six deaths due to acute viscerotropic disease (0.8 deaths per million doses administered) and 45 cases of acute neurotropic disease (5.6 per million doses administered). Yellow fever vaccine recommendations were revised to include areas in Brazil previously not considered at risk for yellow fever.

West Nile virus and kidney disease

West Nile virus (WNV), the causative agent of West Nile fever and West Nile neuroinvasive disease in humans, has become endemic in many countries in all continents. Concerns on long-term mobility from WNV have arisen from recent studies that reported chronic kidney disease in patients who recovered from WNV infection, supported by data from animal models that showed prolonged excretion of the virus with urine. The purpose of this review is to summarize and discuss the results of studies in the literature that investigated WNV infection of the kidney in humans and in animal models and WNV excretion with urine, the potential damage to the kidney caused by WNV infection, the risk of WNV disease in kidney transplant recipients, the significance of detecting WNV in urine and its use in the diagnosis of WNV infection, and kidney involvement by other mosquito-borne flaviviruses.

Yellow fever epizootics in non-human primates, São Paulo state, Brazil, 2008-2009

Since 2000, the expansion of Sylvatic Yellow Fever (YF) has been observed in the southeast of Brazil, being detected in areas considered silent for decades. Epizootics in non-human primates (NHPs) are considered sentinel events for the detection of human cases. It is important to report epizootic events that could have impact on the conservation status of susceptible species. We describe the epizootics in NHPs, notified in state of São Paulo, Brazil, between September 2008 to August 2009. Ninety-one epizootic events, involving 147 animals, were reported in 36 counties. Samples were obtained from 65 animals (44.2%). Most of the epizootics (46.6%) were reported between March and April, the same period during which human cases of YF occurred in the state. Biological samples were collected from animals found dead and were sent to Instituto Adolfo Lutz, in São Paulo. Two samples, collected in two counties without an indication for YF vaccination, were positive for the virus. Another 48 animals were associated with YF by clinical-epidemiological linkage with laboratory confirmed cases. Because the disease in human and NHPs occurred in the same period, the detection of the virus in NHPs did not work as sentinel, but aided in the delineation of new areas of risk.

Reemergence of yellow fever: detection of transmission in the State of São Paulo, Brazil, 2008

INTRODUCTION

Following yellow fever virus (YFV) isolation in monkeys from the São José do Rio Preto region and two fatal human autochthonous cases from the Ribeirão Preto region, State of São Paulo, Brazil, two expeditions for entomological research and eco-epidemiological evaluation were conducted.

METHODS

A total of 577 samples from humans, 108 from monkeys and 3,049 mosquitoes were analyzed by one or more methods: virus isolation, ELISA-IgM, RT-PCR, histopathology and immunohistochemical.

RESULTS

Of the 577 human samples, 531 were tested by ELISA-IgM, with 3 positives, and 235 were inoculated into mice and 199 in cell culture, resulting in one virus isolation. One sample was positive by histopathology and immunohistochemical. Using RT-PCR, 25 samples were processed with 4 positive reactions. A total of 108 specimens of monkeys were examined, 108 were inoculated into mice and 45 in cell culture. Four virus strains were isolated from Alouatta caraya. A total of 931 mosquitoes were captured in Sao Jose do Rio Preto and 2,118 in Ribeirão Preto and separated into batches. A single isolation of YFV was derived from a batch of 9 mosquitoes Psorophora ferox, collected in Urupês, Ribeirão Preto region. A serological survey was conducted with 128 samples from the municipalities of São Carlos, Rincão and Ribeirão Preto and 10 samples from contacts of patients from Ribeirão Preto. All samples were negative by ELISA-IgM for YFV.

CONCLUSIONS

The results confirm the circulation of yellow fever, even though sporadic, in the Sao Paulo State and reinforce the importance of vaccination against yellow fever in areas considered at risk.

Autonomic nervous dysfunction in hamsters infected with West Nile virus

Clinical studies and case reports clearly document that West Nile virus (WNV) can cause respiratory and gastrointestinal (GI) complications. Other functions controlled by the autonomic nervous system may also be directly affected by WNV, such as bladder and cardiac functions. To investigate how WNV can cause autonomic dysfunctions, we focused on the cardiac and GI dysfunctions of rodents infected with WNV. Infected hamsters had distension of the stomach and intestines at day 9 after viral challenge. GI motility was detected by a dye retention assay; phenol red dye was retained more in the stomachs of infected hamsters as compared to sham-infected hamsters. The amplitudes of electromygraphs (EMGs) of intestinal muscles were significantly reduced. Myenteric neurons that innervate the intestines, in addition to neurons in the brain stem, were identified to be infected with WNV. These data suggest that infected neurons controlling autonomic function were the cause of GI dysfunction in WNV-infected hamsters. Using radiotelemetry to record electrocardiograms and to measure heart rate variability (HRV), a well-accepted readout for autonomic function, we determined that HRV and autonomic function were suppressed in WNV-infected hamsters. Cardiac histopathology was observed at day 9 only in the right atrium, which was coincident with WNV staining. A subset of WNV infected cells was identified among cells with hyperplarization-activated cyclic nucleotide-gated potassium channel 4 (HCN4) as a marker for cells in the sinoatrial (SA) and atrioventricular (AV) nodes. The unique contribution of this study is the discovery that WNV infection of hamsters can lead to autonomic dysfunction as determined by reduced HRV and reduced EMG amplitudes of the GI tract. These data may model autonomic dysfunction of the human West Nile neurological disease.

Yellow fever: a reemerging threat

Yellow fever (YF) is a viral disease, endemic to tropical regions of Africa and the Americas, which principally affects humans and nonhuman primates and is transmitted via the bite of infected mosquitoes. Yellow fever virus (YFV) can cause devastating epidemics of potentially fatal, hemorrhagic disease. Despite mass vaccination campaigns to prevent and control these outbreaks, the risk of major YF epidemics, especially in densely populated, poor urban settings, both in Africa and South America, has greatly increased. Consequently, YF is considered an emerging, or reemerging disease of considerable importance. This article comprehensively reviews the history, microbiology, epidemiology, clinical presentation, diagnosis, and treatment of YFV, as well as the vaccines produced to combat YF.

Infectious diseases in paediatric pathology: experience from a developing country

Infectious and parasitic diseases have always challenged man. Although many of them are typically seen in some areas of the world and can be adequately managed by just improving socioeconomic status and sanitary conditions, they are still quite prevalent and may sometimes be seen outside their original geographical areas. Human migration due to different reasons, tourism, blood transfusion and solid organ transplantation has created new concerns for health professionals all over the world. If not for diagnostic purposes, at least these tropical and infectious diseases should be largely known because their epidemiology, pathogenesis, host/parasite interaction, inflammatory and reparative responses are quite interesting and teach us about human biology. Curiosity is inherent to pathology practice and so we are compelled to look for things other than tumours or degenerative diseases. This review focuses on infectious and parasitic diseases found in a developing country and brings up-to-date information on diseases caused by viruses (dengue, yellow fever), bacteria (typhoid fever, leprosy), parasites (Chagas' disease, cutaneous and visceral leishmaniasis, amoebiasis, Capillaria hepatica, schistosomiasis, cysticercosis) and caused by fungi (paracoccidioidomycosis, cryptococcosis, histoplasmosis) that may be useful for pathologists when facing somewhat strange cases from developing countries.

Application of immunohistochemistry to infections

CONTEXT

Pathologists play an important role in the diagnosis or exclusion of infectious diseases. Traditionally, the diagnosis of infectious diseases rely on serologic assays and cultures. Serologic results may be difficult to interpret in the setting of immunosuppression, fresh tissue is not always available for culture, and culture of fastidious pathogens can be difficult and may take weeks or months to yield a result. Although some microorganisms or their cytopathic effects may be readily identifiable on routine and/or histochemical stains, often these changes are not specific or are sparse in the sample evaluated. In these cases, additional immunohistochemical stains are often needed to establish the diagnosis of infection.

OBJECTIVE

To review the current value and limitations of the use of immunohistochemistry in the diagnosis of infectious diseases in formalin-fixed tissue samples.

DATA SOURCES

Literature in Medline and the authors' own experience.

CONCLUSIONS

Immunohistochemistry has proven to be a useful tool in the diagnosis of infectious diseases in tissue samples. Immunohistochemistry is especially useful in the identification of microorganisms that are present in low numbers, stain poorly, are fastidious to grow, are noncultivable, or exhibit an atypical morphology. Finally, it is important to remember that there may be widespread occurrence of common antigens among bacteria and pathogenic fungi and both monoclonal and polyclonal antibodies must be tested for possible cross-reactivity with other organisms.

Viral hemorrhagic fevers

A taxonomically diverse set of single-stranded ribonucleic acid(ssRNA) viruses from four diverse viral families Arenaviridae,Bunyaviridae, Filoviridae, and Flaviviridae cause an acute systemic febrile syndrome called viral hemorrhagic fever (VHF). The syndrome produces combinations of prostration, malaise, increased vascular permeability, and coagulation maladies. In severe illness,VHF may include generalized bleeding but the bleeding does not typically constitute a life-threatening loss of blood volume. To a certain extent, it is a sign of damage to the vascular endothelium and is an indicator of disease severity in specific target organs. Although the viruses that cause hemorrhagic fever (HF) can productively replicate in endothelial cells, much of the disease pathology including impairment to the vascular system is thought to result primarily from the release of a variety of mediators from virus-infected cells, such as monocytes and macrophages that subsequently alter vascular function and trigger the coagulation disorders that epitomize these infections. While significant progress has been made over the last several years in dissecting out the molecular biology and pathogenesis of the HF viruses, there are currently no vaccines or drugs licensed available for most of the VHFs.

Comparison of the inhibitory effects of interferon alfacon-1 and ribavirin on yellow fever virus infection in a hamster model

Antiviral compounds were evaluated for efficacy against yellow fever virus (YFV) in a hamster model of YFV-induced liver disease. Challenge with a 10(2) 50% cell culture infectious doses of YFV resulted in a 50-80% mortality rate in female hamsters. Virus was detected by quantitative real-time RT-PCR (QRT-PCR) in liver, kidney, spleen and serum with peak titers on 4-6 days post-viral challenge (dpi). Serum levels of alkaline phosphatase, alanine aminotransferase (ALT), bilirubin, blood urea nitrogen, potassium and creatinine were significantly elevated, while serum levels of albumin, amylase, glucose, calcium, globulin, phosphorus, sodium and total protein were significantly reduced. Packed cell volume and white blood cell count were significantly elevated during the course of the infection. Intraperitoneal treatment of hamsters with 0.5-5 microg/kg/day interferon (IFN) alfacon-1, 100mg/kg/day viramidine or 50 mg/kg/day ribavirin, initiated 4h prior to YFV challenge, resulted in significant improvement in survival and serum ALT levels. Treatment with IFN alfacon-1 or ribavirin starting 2dpi, also significantly improved survival and serum ALT levels in hamsters challenged with YFV. Pre- and post-virus exposure treatment with IFN alfacon-1 was efficacious in improving disease in YFV-infected hamsters.

Revisiting the liver in human yellow fever: Virus-induced apoptosis in hepatocytes associated with TGF-β, TNF-α and NK cells activity

Flavivirus infection as dengue and yellow fever persists as a terrible menace to pandemics, due to Aedes prevalence in the Americas. Yellow fever is characterized by hepatocyte damage, with steatosis, apoptosis and necrosis, mainly in the midzonal region of the liver, but the injury mechanism has not been studied at the light of recent knowledge, such as the advances in cell death mechanisms, inflammatory response and cytokine cell expression tools. We studied 53 human liver paraffin embedded blocks from patients who died with yellow fever, all with histological demonstration of higher prevalence of apoptosis over necrosis and mild disproportionate inflammatory response. Viral antigens were found most frequently in hepatocytes from the midzonal area than other lobule areas, as detected by specific immunohistochemistry. Infiltrating cell subpopulations showed mainly CD4+ T lymphocytes, with small numbers of CD8+ cytotoxic lymphocytes, CD20+ B lymphocytes, NKT+ cells and S100+ dendritic cells in the sites of inflammation, as compared to normal and leptospirosis liver blocks. Some cells expressed TNF-alpha and IFN-gamma, but a much more intense proportion of TGF-beta expressing cells were found, suggesting both a Th1 and Th3 patterns of immune response in yellow fever. Most affected hepatocyte presented apoptosis markers that appear at the cell death main pathway in this infection. Viral antigens, which production could interfere in hepatocyte biology, could induce the activation of apoptosis cascade, but TGF-beta was also an apoptosis promoter. Our finding supports the key effect of the yellow fever virus in hepatocyte injury, resulting in prevalence of apoptosis over necrosis, aside from a TGF-beta action induced by the inflammatory response.

Midzonal lesions in yellow fever: A specific pattern of liver injury caused by direct virus action and in situ inflammatory response

Yellow fever is an acute infectious, non-contagious disease characterized by intense vasculopathy and lesions in different organs. In the liver, one of the main targets of the virus, the infection induces a characteristic midzonal injury characterized by hepatocyte necrosis, apoptosis and steatosis. This characteristics pattern of liver injury in yellow fever is also observed in conditions of low-flow hypoxia and other infections such as dengue and Rift Valley fever. There are no reports in the literature explaining the genesis of this peculiar histopathological pattern in yellow fever. Some hypotheses have been proposed to explain the mechanism of this midzonal distribution pattern observed in the liver such as low-flow hypoxia and tropism of the virus toward hepatocytes in this area. These hypotheses are discussed in view of more recent findings regarding the pathogenesis of yellow fever and regarding hepatic physiopathology, and a new hypothesis is proposed: the midzonal necrosis is consequence of action of combined factors mainly the direct cytopathic effect of YFV associated with a potent immune response in which CD4+ and CD8+ lymphocytes and the cytokines, especially TGF-beta, but also TNF-alpha and IFN-gamma play an important role.

Immunohistochemical examination of the role of Fas ligand and lymphocytes in the pathogenesis of human liver yellow fever

Yellow fever is an infectious, non-contagious disease caused by an RNA virus of the family Flaviviridae, which is transmitted to man by the bite of hematophagous mosquitoes. Infection with the yellow fever virus can progress with lesions in the heart, kidneys, central nervous system, and liver. In the liver, the histopathological picture is characterized by necrosis, steatosis and hepatocyte apoptosis, with a preferential midzone distribution. In the present study, liver samples from fatal patients with yellow fever were analyzed. The histopathological pattern was characterized by steatosis, lytic necrosis and hepatocyte apoptosis associated with a moderate mononuclear inflammatory infiltrate. The inflammatory component mainly consisted of CD4+ T lymphocytes, followed by CD8+ T lymphocytes, which showed a preferential portal and midzone distribution. Immunoreactivity to Fas ligand was mainly observed in hepatocytes of the midzone region. Based on these findings, we conclude that lymphocytes play an important role in the genesis of hepatic lesions in severe yellow fever, inducing hepatocyte apoptosis through the binding to Fas receptors. However, further studies are necessary to investigate the participation of other immune factors and to quantify the role of the cytotoxic cellular response in the lesion evolution during the course of disease in the liver.

Reconsideration of histopathology and ultrastructural aspects of the human liver in yellow fever

Yellow fever is a re-emerging infectious disease that currently is at risk of urbanization due to the advance of the Aedes aegypti vector. The disease affects about 200,000 individuals annually, mainly in tropical Africa and South America. It causes severe disease involving especially the liver, with lesions characterized by midzonal steatosis, apoptosis and lytic necrosis of the hepatocytes. Quantitative histological and immunohistochemical analysis of 53 human hepatic samples demonstrated apoptosis, steatosis and lytic necrosis of hepatocytes with midzonal pattern. No substantial alterations and reticular network were observed. The inflammatory infiltrate consisted of mononuclear cells and intensity was minimal or moderate, disproportionate to the intense death of the hepatocytes. Hepatic damage in yellow fever resulted mainly from a massive death of hepatocytes due to apoptosis and to a lesser extent due to lytic necrosis. It is recommended that therapeutic regimens for serious cases should include measures to protect against apoptosis.

Exotic emerging viral diseases: progress and challenges

The agents causing viral hemorrhagic fever (VHF) are a taxonomically diverse group of viruses that may share commonalities in the process whereby they produce systemic and frequently fatal disease. Significant progress has been made in understanding the biology of the Ebola virus, one of the best known examples. This knowledge has guided our thinking about other VHF agents, including Marburg, Lassa, the South American arenaviruses, yellow fever, Crimean-Congo and Rift Valley fever viruses. Comparisons among VHFs show that a common pathogenic feature is their ability to disable the host immune response by attacking and manipulating the cells that initiate the antiviral response. Of equal importance, these comparisons highlight critical gaps in our knowledge of these pathogens.

A case of yellow fever in a brown howler (Alouatta fusca) in Southern Brazil

Many brown howlers (Alouatta fusca) have died in a 3-month period in a subtropical forest in Southern Brazil. One was examined after a systemic illness. According to clinical signs, and necropsy and histopathology findings, yellow fever virus (YFV) infection was suspected. Tissue sections from liver, kidney, and lymphoid organs were screened by immunohistochemistry for YFV antigens. Cells within those tissues stained positively with a polyclonal antibody against YFV antigens (1:1,600 dilution), and yellow fever was diagnosed for the first time in the brown howler in the area.

Detection of yellow fever virus: a comparison of quantitative real-time PCR and plaque assay

Yellow fever virus quantitation is performed routinely by cultivation of virus containing samples using susceptible cells. Counting of the resulting plaques provides a marker for the number of infectious particles present in the sample. This assay usually takes up to 5 days before results are obtained and must be carried out under L2 or L3 laboratory conditions, depending on the yellow fever virus strain used. For clinical diagnosis of yellow fever virus infections the cell culture-based approach takes too long and is of limited practical relevance. Recently, due to its considerable sensitivity, PCR has become a promising method for virus detection. However, whilst PCR can detect virus-specific nucleic acids, it does not allow conclusions to be drawn regarding the infectious potential of the virus detected. Nonetheless, for diagnostic purposes, a rapid, specific and sensitive virus PCR is preferable. Therefore, two independent yellow fever virus-specific real-time PCR assays were established and compared the viral RNA loads to the results of a traditional plaque assay. The estimated ratio of yellow fever virus genomes to infectious particles was between 1000:1 and 5000:1; both approaches displayed a comparable precision of <45%. A significant correlation between genome number as determined by real-time PCR and the corresponding number of plaques in paired samples was found with a Pearson coefficient of correlation of r=0.88 (P<0.0001).

Pathogenesis and Pathophysiology of Yellow Fever

It will be apparent to the reader that there is much to learn about the pathogenesis of YF. The role of specific genes and molecular determinants of neurotropism and viscerotropism has been defined only partially. The availability of infectious clones and a small animal (hamster) model should allow dissection of virulence factors, which can then be tested in the more difficult monkey model. The marked differences between wild-type YF strains should be evaluated by evaluating the relationships between virulence and genome sequence. The role of cytokine dysregulation and endothelial injury in YF will be elucidated as access to patients and of patients to more sophisticated medical care improves. The number of cases of YF in unvaccinated travelers hospitalized after return from the tropics has unfortunately increased, but such cases afford unique opportunities to study the pathogenesis of renal failure, coagulopathy, vascular instability, and shock, as well as new treatment modalities. At the cellular level, there are also important opportunities for research on YF virus-cell receptor interactions, the control of apoptotic cell death, and the predilection for cells of the midzone of the liver lobule. The role of dendritic cells in the early stage of YF infection is deserving of study. Finally, the role of the immune response to infection, particularly cellular immunity, is poorly characterized, and the suggestion that immune clearance may aggravate the condition of the host during the period of intoxication should be evaluated in appropriate animal models.