Risk factors for encephalitis and death from West Nile virus infection

Diabetes mellitus as a risk factor for severe dengue fever and West Nile fever: A meta-analysis

BACKGROUND

Dengue fever (DF) and West Nile fever (WNF) have become endemic worldwide in the last two decades. Studies suggest that individuals with diabetes mellitus (DM) are at a higher risk of developing severe complications from these diseases. Identifying the factors associated with a severe clinical presentation is crucial, as prompt treatment is essential to prevent complications and fatalities. This article aims to summarize and assess the published evidence regarding the link between DM and the risk of severe clinical manifestations in cases of DF and WNF.

METHODOLOGY/PRINCIPAL FINDINGS

A systematic search was conducted using the PubMed and Web of Science databases. 27 studies (19 on DF, 8 on WNF) involving 342,873 laboratory-confirmed patients were included in the analysis. The analysis showed that a diagnosis of DM was associated with an increased risk for severe clinical presentations of both DF (OR 3.39; 95% CI: 2.46, 4.68) and WNF (OR 2.89; 95% CI: 1.89, 4.41). DM also significantly increased the risk of death from both diseases (DF: OR 1.95; 95% CI: 1.09, 3.52; WNF: OR 1.74; 95% CI: 1.40, 2.17).

CONCLUSIONS/SIGNIFICANCE

This study provides strong evidence supporting the association between DM and an increased risk of severe clinical manifestations in cases of DF and WNF. Diabetic individuals in DF or WNF endemic areas should be closely monitored when presenting with febrile symptoms due to their higher susceptibility to severe disease. Early detection and appropriate management strategies are crucial in reducing the morbidity and mortality rates associated with DF and WNF in diabetic patients. Tailored care and targeted public health interventions are needed to address this at-risk population. Further research is required to understand the underlying mechanisms and develop effective preventive and therapeutic approaches.

George K, Hoang HE, Thakur KT. Clinical and Diagnostic Features of West Nile Virus Neuroinvasive Disease in New York City

West Nile virus (WNV) neuroinvasive disease (WNND) occurs in approximately 1 percent of WNV-infected patients and typically presents as encephalitis, meningitis, or acute flaccid paralysis (AFP). WNND remains a difficult inpatient diagnosis, creating significant challenges for prognostication and therapy selection. We characterized the clinical and diagnostic features of WNND cases at two major academic medical centers in New York City in routine clinical practice. We retrospectively reviewed the charts of thirty-six patients with WNND, including twenty-six encephalitis, four meningitis, and six AFP cases. The most common presenting symptoms were fever (86.1%) and gastrointestinal symptoms (38.9%) in addition to altered mental status (72.2%), lethargy (63.9%), gait disturbances (46.2%), and headache (44.4%). Fourteen (48.3%) patients displayed acute magnetic resonance imaging (MRI) findings, particularly T2 hyperintensities in the bilateral thalami, brainstem, and deep white matter. New York State Department of Health WNV CSF IgM testing was utilized for diagnosis in 58.3% of patients; however, just 38.1% had the result by discharge, compared to 85.6% of those who underwent serum IgM testing. The median length of stay was 13.5 days, 38.9% were intubated, and three patients (8.9%) died during acute hospitalization. Our findings underscore the morbidity, mortality, and diagnostic challenges of WNND, suggesting the potential utility of serum IgM testing in combination with confirmatory CSF testing to expedite diagnosis in the acute setting.

Infectious Diseases Among People Experiencing Homelessness: A Systematic Review of the Literature in the United States and Canada, 2003-2022

Homelessness increases the risk of acquiring an infectious disease. We conducted a systematic review of the literature to identify quantitative data related to infectious diseases and homelessness. We searched Google Scholar, PubMed, and SCOPUS for quantitative literature published from January 2003 through December 2022 in English from the United States and Canada. We excluded literature on vaccine-preventable diseases and HIV because these diseases were recently reviewed. Of the 250 articles that met inclusion criteria, more than half were on hepatitis C virus or Mycobacterium tuberculosis. Other articles were on COVID-19, respiratory syncytial virus, Staphylococcus aureus, group A Streptococcus, mpox (formerly monkeypox), 5 sexually transmitted infections, and gastrointestinal or vectorborne pathogens. Most studies showed higher prevalence, incidence, or measures of risk for infectious diseases among people experiencing homelessness as compared with people who are housed or the general population. Although having increased published data that quantify the infectious disease risks of homelessness is encouraging, many pathogens that are known to affect people globally who are not housed have not been evaluated in the United States or Canada. Future studies should focus on additional pathogens and factors leading to a disproportionately high incidence and prevalence of infectious diseases among people experiencing homelessness.

Autoantibodies neutralizing type I IFNs underlie West Nile virus encephalitis in ∼40% of patients

Mosquito-borne West Nile virus (WNV) infection is benign in most individuals but can cause encephalitis in <1% of infected individuals. We show that ∼35% of patients hospitalized for WNV disease (WNVD) in six independent cohorts from the EU and USA carry auto-Abs neutralizing IFN-α and/or -ω. The prevalence of these antibodies is highest in patients with encephalitis (∼40%), and that in individuals with silent WNV infection is as low as that in the general population. The odds ratios for WNVD in individuals with these auto-Abs relative to those without them in the general population range from 19.0 (95% CI 15.0-24.0, P value <10-15) for auto-Abs neutralizing only 100 pg/ml IFN-α and/or IFN-ω to 127.4 (CI 87.1-186.4, P value <10-15) for auto-Abs neutralizing both IFN-α and IFN-ω at a concentration of 10 ng/ml. These antibodies block the protective effect of IFN-α in Vero cells infected with WNV in vitro. Auto-Abs neutralizing IFN-α and/or IFN-ω underlie ∼40% of cases of WNV encephalitis.

Comparison of West Nile Virus Disease in Humans and Horses: Exploiting Similarities for Enhancing Syndromic Surveillance

West Nile virus (WNV) neuroinvasive disease threatens the health and well-being of horses and humans worldwide. Disease in horses and humans is remarkably similar. The occurrence of WNV disease in these mammalian hosts has geographic overlap with shared macroscale and microscale drivers of risk. Importantly, intrahost virus dynamics, the evolution of the antibody response, and clinicopathology are similar. The goal of this review is to provide a comparison of WNV infection in humans and horses and to identify similarities that can be exploited to enhance surveillance methods for the early detection of WNV neuroinvasive disease.

Outcomes of RIP Kinase Signaling During Neuroinvasive Viral Infection

Neuroinvasive viral diseases are a considerable and growing burden on global public health. Despite this, these infections remain poorly understood, and the molecular mechanisms that govern protective versus pathological neuroinflammatory responses to infection are a matter of intense investigation. Recent evidence suggests that necroptosis, an immunogenic form of programmed cell death, may contribute to the pathogenesis of viral encephalitis. However, the receptor-interacting protein (RIP) kinases that coordinate necroptosis, RIPK1 and RIPK3, also appear to have unexpected, cell death-independent functions in the central nervous system (CNS) that promote beneficial neuroinflammation during neuroinvasive infection. Here, we review the emerging evidence in this field, with additional discussion of recent work examining roles for RIPK signaling and necroptosis during noninfectious pathologies of the CNS, as these studies provide important additional insight into the potential for specialized neuroimmune functions for the RIP kinases.

Neuroinvasive West Nile virus infections after solid organ transplantation: Single center experience and systematic review

West Nile virus (WNv) is a major cause of viral encephalitis in the United States. WNv infection is usually asymptomatic or a limited febrile illness in the immunocompetent hosts, although a small percentage can develop neuroinvasive disease. Neuroinvasive disease due to WNv in solid organ transplant recipients occurs at higher rates than observed in the general population and can have long term neurological sequalae.

METHODS

We retrospectively reviewed medical records of all solid organ transplant recipients at our institution who tested positive for WNv from 2010 to 2018. Two reviewers performed electronic searches of Medline, Embase, Cochrane Library of literature of WNv infections in SOT. Descriptive statistics were performed on key variables.

RESULTS

Eight recipients (mean age 54, five males) were diagnosed with neuroinvasive WNv infection at our institution. Distribution of infection was as follows: five kidney transplants, one in each kidney-pancreas, liver, and lung. Diagnoses included meningitis (3), encephalitis (1), meningo-encephalitis (4). Median time from transplant to infection was 49.8 months (2.7-175.4). No infections were considered donor-derived. Five patients received treatment with IVIG. Six patients were alive at median follow-up of 49.5 months (21.7-116.8). We identified 29 studies published from 2002 to 2019. Median time from transplant to infection was 14.2 months, with similar allograft distribution; 53% were donor-derived infections.

CONCLUSION

WNv infections in solid organ transplant recipients can be a consequence of organ donation or can be acquired via the community. Infections can be more severe in SOT recipients and lead to neuroinvasive disease.

West Nile Disease Symptoms and Comorbidities: A Systematic Review and Analysis of Cases

West Nile virus (WNV) is a mosquito-borne flavivirus that has emerged as a major cause of viral encephalitis and meningitis, rarely leading to death. Several risk factors have been discussed in the past concerning the severity of the disease, while few reports have focused on precipitating conditions that determine of WNV-related death. Studies on cohorts of patients suffering of West Nile disease (WND) usually encompass low numbers of deceased patients as a result of the rarity of the event. In this systematic review and critical analysis of 428 published case studies and case series, we sought to evaluate and highlight critical parameters of WND-related death. We summarized the symptoms, comorbidities, and treatment strategies related to WND in all published cases of patients that included clinical features. Symptoms such as altered mental status and renal problems presented increased incidence among deceased patients, while these patients presented increased cerebrospinal fluid (CSF) glucose. Our analysis also highlights underestimated comorbidities such as pulmonary disease to act as precipitating conditions in WND, as they were significantly increased amongst deceased patients. CSF glucose and the role of pulmonary diseases need to be revaluated either retrospectively or prospectively in WND patient cohorts, as they may be linked to increased mortality risk.

A Preliminary Study of Proinflammatory Cytokines and Depression Following West Nile Virus Infection

West Nile virus (WNV) is a neurotropic flavivirus that can cause acute febrile illness leading to neuroinvasive disease. Depression is a well-described outcome following infection, but the underlying pathogenic mechanisms are unknown. Proinflammatory cytokines play important roles in WNV infection, but their role in depression post-WNV remains unstudied. This research aimed to retrospectively evaluate associations between proinflammatory cytokines and new onset depression in a WNV cohort. Participants with asymptomatic WNV infection were significantly less likely to report new onset depression when compared to those with symptomatic disease. Participants with encephalitis and obesity were significantly more likely to report new onset depression post-infection. Based on univariate analysis of 15 antiviral or proinflammatory cytokines, depression was associated with elevated MCP-1 and decreased TNFα, whereas G-CSF was significantly elevated in those with a history of neuroinvasive WNV. However, no cytokines were statistically significant after adjusting for multiple comparisons using the Bonferroni method. While symptomatic WNV infection, encephalitis, and obesity were associated with new onset depression following infection, the role of proinflammatory cytokines requires additional studies. Further research involving paired acute-convalescent samples, larger sample sizes, and additional data points would provide additional insight into the impact of the inflammatory response on WNV-mediated depression.

Comorbid conditions as risk factors for West Nile neuroinvasive disease in Ontario, Canada: a population-based cohort study

West Nile neuroinvasive disease (WNND) is a severe neurological illness that can result from West Nile virus (WNV) infection, with long-term disability and death being common outcomes. Although WNV arrived in North America over two decades ago, risk factors for WNND are still being explored. The objective of this study was to identify WNND comorbid risk factors in the Ontario population using a retrospective, population-based cohort design. Incident WNV infections from laboratory records between 1 January 2002 – 31 December 2012 were individually-linked to health administrative databases to ascertain WNND outcomes and comorbid risk factors. WNND incidence was compared among individuals with and without comorbidities using risk ratios (RR) calculated with log binomial regression.

Three hundred and forty-five individuals developed WNND (18.3%) out of 1884 WNV infections. West Nile encephalitis was driving most associations with comorbidities. Immunocompromised (aRR 2.61 [95% CI 1.23–4.53]) and male sex (aRR 1.32 [95% CI 1.00–1.76]) were risk factors for encephalitis, in addition to age, for which each 1-year increase was associated with a 2% (aRR 1.02 [95% CI 1.02–1.03]) relative increase in risk. Our results suggest that individuals living with comorbidities are at higher risk for WNND, in particular encephalitis, following WNV infection.

Encephalitis Caused by Jamestown Canyon Virus in a Liver Transplant Patient, North Carolina, USA, 2017

We describe the first documented case of Jamestown Canyon Virus (JCV) in North Carolina, which occurred in a liver transplant patient who presented acutely with headache, aphasia, and confusion. This is also the first report of recovery from JCV encephalitis following treatment with intravenous immune globulin.

Approach to Limb Weakness

"Approach to limb weakness" provides an overview of the pathways of the motor system and the type of weakness seen with pathology at each level from the cortex to the muscle. This article provides the clinical pearls needed to identify different patterns of weakness and accurately localize the level of weakness. It offers important pointers that help distinguish among the different etiologies of weakness at each level, as well as various diagnostic approaches and treatments of diseases that lead to limb weakness. The diagnoses discussed are meant to be representative and not exhaustive, as a complete differential for each pattern of weakness is beyond the scope of this article.

Obesity Enhances Disease Severity in Female Mice Following West Nile Virus Infection

A rise in adiposity in the United States has resulted in more than 70% of adults being overweight or obese, and global obesity rates have tripled since 1975. Following the 2009 H1N1 pandemic, obesity was characterized as a risk factor that could predict severe infection outcomes to viral infection. Amidst the SARS-CoV-2 pandemic, obesity has remained a significant risk factor for severe viral disease as obese patients have a higher likelihood for developing severe symptoms and requiring hospitalization. However, the mechanism by which obesity enhances viral disease is unknown. In this study, we utilized a diet-induced obesity mouse model of West Nile virus (WNV) infection, a flavivirus that cycles between birds and mosquitoes and incidentally infects both humans and mice. Likelihood for severe WNV disease is associated with risk factors such as diabetes that are comorbidities also linked to obesity. Utilizing this model, we showed that obesity-associated chronic inflammation increased viral disease severity as obese female mice displayed higher mortality rates and elevated viral titers in the central nervous system. In addition, our studies highlighted that obesity also dysregulates host acute adaptive immune responses, as obese female mice displayed significant dysfunction in neutralizing antibody function. These studies highlight that obesity-induced immunological dysfunction begins at early time points post infection and is sustained through memory phase, thus illuminating a potential for obesity to alter the differentiation landscape of adaptive immune cells.

West Nile Virus-Associated Hospitalizations, California, 2004-2017

BACKGROUND

West Nile virus (WNV) is the most commonly reported mosquito-borne disease in the USA. California reports more WNV disease than any other state.

METHODS

We identified WNV-associated hospitalizations from 2004 through 2017 in California and estimated hospitalization incidence using Patient Discharge Data. We described demographic, geographic, and clinical characteristics of WNV hospitalizations; identified risk factors for in-hospital death; and tabulated hospitalization charges.

RESULTS

From 2004 through 2017, 3109 Californians were hospitalized with WNV (median, 214 patients/year; range, 72-449). The majority were male (1983; 63.8%) and aged ≥60 years (1766; 56.8%). The highest median annual hospitalization rate (0.88 hospitalizations/100 000 persons) was in the Central Valley, followed by southern California (0.59 hospitalizations/100 000 persons). Most patients (2469; 79.4%) had ≥1 underlying condition, including hypertension, cardiovascular disease, diabetes, chronic kidney disease, or immunosuppression due to medications or disease. Median hospitalization length of stay was 12 days (interquartile range, 6-23 days). During hospitalization, 1317 (42%) patients had acute respiratory failure and/or sepsis/septic shock, 772 (24.8%) experienced acute kidney failure, and 470 (15.1%) had paralysis; 272 (8.8%) patients died. Nearly 47% (1444) of patients were discharged for additional care. During these 14 years, $838 680 664 (mean $59.9 million/year) was charged for WNV hospitalizations, 73.9% through government payers at a median charge of $142 321/patient.

CONCLUSIONS

WNV-associated hospitalizations were substantial and costly in California. Hospitalization incidence was higher in males, elderly persons, and patients with underlying conditions. WNV persists as a costly and severe public health threat in California.

Immunoinformatics and molecular dynamics approaches: Next generation vaccine design against West Nile virus

West Nile Virus (WNV) is a life threatening flavivirus that causes significant morbidity and mortality worldwide. No preventive therapeutics including vaccines against WNV are available for human use. In this study, immunoinformatics approach was performed to design a multi epitope-based subunit vaccine against this deadly pathogen. Human (HLA) and Mice (H-2) allele specific potential T-cell and B-cell epitopes were shortlisted through a stringent procedure. Molecular docking showed selected epitopes that have stronger binding affinity with human TLR-4. Molecular dynamics simulation confirmed the stable nature of the docked complex. Furthermore, in silico cloning analysis ensures efficient expression of desired gene in the microbial system. Interestingly, previous studies showed that two of our selected epitopes have strong immune response against WNV. Therefore, selected epitopes could be strong vaccine candidates to prevent WNV infections in human. However, further in vitro and in vivo investigations could be strengthening the validation of the vaccine candidate against WNV.

Surveillance for West Nile virus disease - United States, 2009-2018

PROBLEM/CONDITION

West Nile virus (WNV) is an arthropod-borne virus (arbovirus) in the family Flaviviridae and is the leading cause of domestically acquired arboviral disease in the contiguous United States. An estimated 70%-80% of WNV infections are asymptomatic. Symptomatic persons usually develop an acute systemic febrile illness. Less than 1% of infected persons develop neuroinvasive disease, which typically presents as encephalitis, meningitis, or acute flaccid paralysis.

REPORTING PERIOD

2009-2018.

DESCRIPTION OF SYSTEM

WNV disease is a nationally notifiable condition with standard surveillance case definitions. State health departments report WNV cases to CDC through ArboNET, an electronic passive surveillance system. Variables collected include patient age, sex, race, ethnicity, county and state of residence, date of illness onset, clinical syndrome, hospitalization, and death.

RESULTS

During 2009-2018, a total of 21 869 confirmed or probable cases of WNV disease, including 12 835 (59%) WNV neuroinvasive disease cases, were reported to CDC from all 50 states, the District of Columbia, and Puerto Rico. A total of 89% of all WNV patients had illness onset during July-September. Neuroinvasive disease incidence and case-fatalities increased with increasing age, with the highest incidence (1.22 cases per 100 000 population) occurring among persons aged ≥70 years. Among neuroinvasive cases, hospitalization rates were >85% in all age groups but were highest among patients aged ≥70 years (98%). The national incidence of WNV neuroinvasive disease peaked in 2012 (0.92 cases per 100 000 population). Although national incidence was relatively stable during 2013-2018 (average annual incidence: 0.44; range: 0.40-0.51), state level incidence varied from year to year. During 2009-2018, the highest average annual incidence of neuroinvasive disease occurred in North Dakota (3.16 cases per 100 000 population), South Dakota (3.06), Nebraska (1.95), and Mississippi (1.17), and the largest number of total cases occurred in California (2819), Texas (2043), Illinois (728), and Arizona (632). Six counties located within the four states with the highest case counts accounted for 23% of all neuroinvasive disease cases nationally.

INTERPRETATION

Despite the recent stability in annual national incidence of neuroinvasive disease, peaks in activity were reported in different years for different regions of the country. Variations in vectors, avian amplifying hosts, human activity, and environmental factors make it difficult to predict future WNV disease incidence and outbreak locations.

PUBLIC HEALTH ACTION

WNV disease surveillance is important for detecting and monitoring seasonal epidemics and for identifying persons at increased risk for severe disease. Surveillance data can be used to inform prevention and control activities. Health care providers should consider WNV infection in the differential diagnosis of aseptic meningitis and encephalitis, obtain appropriate specimens for testing, and promptly report cases to public health authorities. Public health education programs should focus prevention messaging on older persons because they are at increased risk for severe neurologic disease and death. In the absence of a human vaccine, WNV disease prevention depends on community-level mosquito control and household and personal protective measures. Understanding the geographic distribution of cases, particularly at the county level, appears to provide the best opportunity for directing finite resources toward effective prevention and control activities. Additional work to further develop and improve predictive models that can foreshadow areas most likely to be impacted in a given year by WNV outbreaks could allow for proactive targeting of interventions and ultimately lowering of WNV disease morbidity and mortality.

Age-Related Changes in Thymic Central Tolerance

Thymic epithelial cells (TECs) and hematopoietic antigen presenting cells (HAPCs) in the thymus microenvironment provide essential signals to self-reactive thymocytes that induce either negative selection or generation of regulatory T cells (Treg), both of which are required to establish and maintain central tolerance throughout life. HAPCs and TECs are comprised of multiple subsets that play distinct and overlapping roles in central tolerance. Changes that occur in the composition and function of TEC and HAPC subsets across the lifespan have potential consequences for central tolerance. In keeping with this possibility, there are age-associated changes in the cellular composition and function of T cells and Treg. This review summarizes changes in T cell and Treg function during the perinatal to adult transition and in the course of normal aging, and relates these changes to age-associated alterations in thymic HAPC and TEC subsets.

Surveillance for West Nile Virus Disease - United States, 2009-2018

Problem/Condition

West Nile virus (WNV) is an arthropodborne virus (arbovirus) in the family Flaviviridae and is the leading cause of domestically acquired arboviral disease in the contiguous United States. An estimated 70%–80% of WNV infections are asymptomatic. Symptomatic persons usually develop an acute systemic febrile illness. Less than 1% of infected persons develop neuroinvasive disease, which typically presents as encephalitis, meningitis, or acute flaccid paralysis.

Reporting Period

2009–2018.

Description of System

WNV disease is a nationally notifiable condition with standard surveillance case definitions. State health departments report WNV cases to CDC through ArboNET, an electronic passive surveillance system. Variables collected include patient age, sex, race, ethnicity, county and state of residence, date of illness onset, clinical syndrome, hospitalization, and death.

Results

During 2009–2018, a total of 21,869 confirmed or probable cases of WNV disease, including 12,835 (59%) WNV neuroinvasive disease cases, were reported to CDC from all 50 states, the District of Columbia, and Puerto Rico. A total of 89% of all WNV patients had illness onset during July–September. Neuroinvasive disease incidence and case-fatalities increased with increasing age, with the highest incidence (1.22 cases per 100,000 population) occurring among persons aged ≥70 years. Among neuroinvasive cases, hospitalization rates were >85% in all age groups but were highest among patients aged ≥70 years (98%). The national incidence of WNV neuroinvasive disease peaked in 2012 (0.92 cases per 100,000 population). Although national incidence was relatively stable during 2013–2018 (average annual incidence: 0.44; range: 0.40–0.51), state level incidence varied from year to year. During 2009–2018, the highest average annual incidence of neuroinvasive disease occurred in North Dakota (3.16 cases per 100,000 population), South Dakota (3.06), Nebraska (1.95), and Mississippi (1.17), and the largest number of total cases occurred in California (2,819), Texas (2,043), Illinois (728), and Arizona (632). Six counties located within the four states with the highest case counts accounted for 23% of all neuroinvasive disease cases nationally.

Interpretation

Despite the recent stability in annual national incidence of neuroinvasive disease, peaks in activity were reported in different years for different regions of the country. Variations in vectors, avian amplifying hosts, human activity, and environmental factors make it difficult to predict future WNV disease incidence and outbreak locations.

Public Health Action

WNV disease surveillance is important for detecting and monitoring seasonal epidemics and for identifying persons at increased risk for severe disease. Surveillance data can be used to inform prevention and control activities. Health care providers should consider WNV infection in the differential diagnosis of aseptic meningitis and encephalitis, obtain appropriate specimens for testing, and promptly report cases to public health authorities. Public health education programs should focus prevention messaging on older persons, because they are at increased risk for severe neurologic disease and death. In the absence of a human vaccine, WNV disease prevention depends on community-level mosquito control and household and personal protective measures. Understanding the geographic distribution of cases, particularly at the county level, appears to provide the best opportunity for directing finite resources toward effective prevention and control activities. Additional work to further develop and improve predictive models that can foreshadow areas most likely to be impacted in a given year by WNV outbreaks could allow for proactive targeting of interventions and ultimately lowering of WNV disease morbidity and mortality.

Therapeutic role of inflammasome inhibitors in neurodegenerative disorders

Neuroinflammation, characterized by the activation of glial cells, is a hallmark in several neurological and neurodegenerative disorders. Inadequate inflammation cannot eliminate the infection of pathogens, while excessive or hyper-reactive inflammation can cause chronic or systemic inflammatory diseases affecting the central nervous system (CNS). In response to a brain injury or pathogen invasion, the pathogen recognition receptors (PRRs) expressed on glial cells are activated via binding to cellular damage-associated molecular patterns (DAMPs) or pathogen-associated molecular patterns (PAMPs). This subsequently leads to the activation of NOD (nucleotide-binding oligomerization domain)-like receptor proteins (NLRs). In neurodegenerative diseases such as HIV-1-associated neurocognitive disorders (HAND), Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS), chronic inflammation is a critical contributing factor for disease manifestation including pathogenesis. Emerging evidence points to the involvement of "inflammasomes", especially the nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain-containing (NLRP) complex in the development of these diseases. The activated NLRP3 results in the proteolytic activation of caspase-1 that facilitates the cleavage of pro-IL-1β and the secretion of IL-1β and IL-18 proinflammatory cytokines. Accordingly, these and other seminal findings have led to the development of NLRP-targeting small-molecule therapeutics as possible treatment options for neurodegenerative disorders. In this review, we will discuss the new advances and evidence-based literature concerning the role of inflammasomes in neurodegenerative diseases, its role in the neurological repercussions of CNS chronic infection, and the examples of preclinical or clinically tested NLRP inhibitors as potential strategies for the treatment of chronic neurological diseases.

West Nile virus in California, 2003-2018: A persistent threat

The California Arbovirus Surveillance Program was initiated over 50 years ago to track endemic encephalitides and was enhanced in 2000 to include West Nile virus (WNV) infections in humans, mosquitoes, sentinel chickens, dead birds and horses. This comprehensive statewide program is a function of strong partnerships among the California Department of Public Health (CDPH), the University of California, and local vector control and public health agencies. This manuscript summarizes WNV surveillance data in California since WNV was first detected in 2003 in southern California. From 2003 through 2018, 6,909 human cases of WNV disease, inclusive of 326 deaths, were reported to CDPH, as well as 730 asymptomatic WNV infections identified during screening of blood and organ donors. Of these, 4,073 (59.0%) were reported as West Nile neuroinvasive disease. California's WNV disease burden comprised 15% of all cases that were reported to the U.S. Centers for Disease Control and Prevention during this time, more than any other state. Additionally, 1,299 equine WNV cases were identified, along with detections of WNV in 23,322 dead birds, 31,695 mosquito pools, and 7,340 sentinel chickens. Annual enzootic detection of WNV typically preceded detection in humans and prompted enhanced intervention to reduce the risk of WNV transmission. Peak WNV activity occurred from July through October in the Central Valley and southern California. Less than five percent of WNV activity occurred in other regions of the state or outside of this time. WNV continues to be a major threat to public and wild avian health in California, particularly in southern California and the Central Valley during summer and early fall months. Local and state public health partners must continue statewide human and mosquito surveillance and facilitate effective mosquito control and bite prevention measures.

Emergent Viral Infections of the CNS

Biological evolution of the microbiome continually drives the emergence of human viral pathogens, a subset of which attack the nervous system. The sheer number of pathogens that have appeared, along with their abundance in the environment, demand our attention. For the most part, our innate and adaptive immune systems have successfully protected us from infection; however, in the past 5 decades, through pathogen mutation and ecosystem disruption, a dozen viruses emerged to cause significant neurologic disease. Most of these pathogens have come from sylvatic reservoirs having made the energetically difficult, and fortuitously rare, jump into humans. But the human microbiome is also replete with agents already adapted to the host that need only minor mutations to create neurotropic/toxic agents. While each host/virus symbiosis is unique, this review examines virologic and immunologic principles that govern the pathogenesis of different viral CNS infections that were described in the past 50 years (Influenza, West Nile Virus, Zika, Rift Valley Fever Virus, Hendra/Nipah, Enterovirus-A71/-D68, Human parechovirus, HIV, and SARS-CoV). Knowledge of these pathogens provides us the opportunity to respond and mitigate infection while at the same time prepare for inevitable arrival of unknown agents.

West Nile Virus: An Emerging Threat in Transplant Population

West Nile virus (WNV) has become one of the new challenges for transplant programs. In addition to transmission by mosquito bite, interhuman transmission is possible through blood products or organ transplantation. Majority of WNV infections present as asymptomatic or mild febrile illness, with less than 1% of infected developing neuroinvasive disease. Many studies report naturally acquired or donor-derived WNV infections in solid-organ transplant recipients, mainly kidney, but also liver, heart, lungs and pancreas. Given the much higher risk of neuroinvasive disease (40% and even higher) based on serologic and clinical studies and increased mortality in transplant population, WNV infection should be considered in all patients presented with fever and neurological symptoms after transplantation, especially during the arbovirus transmission season.

Exploring the socio-economic and environmental components of infectious diseases using multivariate geovisualization: West Nile Virus

Background

This study postulates that underlying environmental conditions and a susceptible population's socio-economic status should be explored simultaneously to adequately understand a vector borne disease infection risk. Here we focus on West Nile Virus (WNV), a mosquito borne pathogen, as a case study for spatial data visualization of environmental characteristics of a vector's habitat alongside human demographic composition for understanding potential public health risks of infectious disease. Multiple efforts have attempted to predict WNV environmental risk, while others have documented factors related to human vulnerability to the disease. However, analytical modeling that combines the two is difficult due to the number of potential explanatory variables, varying spatial resolutions of available data, and differing research questions that drove the initial data collection. We propose that the use of geovisualization may provide a glimpse into the large number of potential variables influencing the disease and help distill them into a smaller number that might reveal hidden and unknown patterns. This geovisual look at the data might then guide development of analytical models that can combine environmental and socio-economic data.

Methods

Geovisualization was used to integrate an environmental model of the disease vector's habitat alongside human risk factors derived from socio-economic variables. County level WNV incidence rates from California, USA, were used to define a geographically constrained study area where environmental and socio-economic data were extracted from 1,133 census tracts. A previously developed mosquito habitat model that was significantly related to WNV infected dead birds was used to describe the environmental components of the study area. Self-organizing maps found 49 clusters, each of which contained census tracts that were more similar to each other in terms of WNV environmental and socio-economic data. Parallel coordinate plots permitted visualization of each cluster's data, uncovering patterns that allowed final census tract mapping exposing complex spatial patterns contained within the clusters.

Results

Our results suggest that simultaneously visualizing environmental and socio-economic data supports a fuller understanding of the underlying spatial processes for risks to vector-borne disease. Unexpected patterns were revealed in our study that would be useful for developing future multilevel analytical models. For example, when the cluster that contained census tracts with the highest median age was examined, it was determined that those census tracts only contained moderate mosquito habitat risk. Likewise, the cluster that contained census tracts with the highest mosquito habitat risk had populations with moderate median age. Finally, the cluster that contained census tracts with the highest WNV human incidence rates had unexpectedly low mosquito habitat risk.

The continued threat of emerging flaviviruses

Flaviviruses are vector-borne RNA viruses that can emerge unexpectedly in human populations and cause a spectrum of potentially severe diseases including hepatitis, vascular shock syndrome, encephalitis, acute flaccid paralysis, congenital abnormalities and fetal death. This epidemiological pattern has occurred numerous times during the last 70 years, including epidemics of dengue virus and West Nile virus, and the most recent explosive epidemic of Zika virus in the Americas. Flaviviruses are now globally distributed and infect up to 400 million people annually. Of significant concern, outbreaks of other less well-characterized flaviviruses have been reported in humans and animals in different regions of the world. The potential for these viruses to sustain epidemic transmission among humans is poorly understood. In this Review, we discuss the basic biology of flaviviruses, their infectious cycles, the diseases they cause and underlying host immune responses to infection. We describe flaviviruses that represent an established ongoing threat to global health and those that have recently emerged in new populations to cause significant disease. We also provide examples of lesser-known flaviviruses that circulate in restricted areas of the world but have the potential to emerge more broadly in human populations. Finally, we discuss how an understanding of the epidemiology, biology, structure and immunity of flaviviruses can inform the rapid development of countermeasures to treat or prevent human infections as they emerge.

Reemergence of West Nile Virus Infections in Southern Greece, 2017

Greece experienced the largest European West Nile virus (WNV) outbreak in 2010 since the 1996 Romania epidemic. West Nile virus reemerged in southern Greece during 2017, after a 2-year hiatus of recorded human cases, and herein laboratory findings, clinical features, and geographic distribution of WNV cases are presented. Clinical specimens from patients with clinically suspected WNV infection were sent from local hospitals to the Microbiology Department of Medical School, National and Kapodistrian University of Athens, and were tested for the presence of specific anti-WNV antibodies and WNV RNA. From July to September 2017, 45 confirmed or probable WNV infection cases were identified; 43 of them with an acute/recent infection, of which 24 (55.8%) experienced WNV neuroinvasive disease (WNND). Risk factors for developing WNND included advanced age, hypertension, and diabetes mellitus. A total of four deaths (16.7%) occurred, all in elderly patients aged > 70 years. Thirty-nine cases were identified in regional units that had not been affected before (36 in Argolis and two in Corinth, northeastern Peloponnese, and one in Rethymno, Crete). The remaining four cases were reported from previously affected regional units of northwestern Peloponnese. The reemergence of WNV after a 2-year hiatus of recorded human cases and the spread of the virus in newly affected regions of the country suggests that WNV has been established in Greece and disease transmission will continue in the future. Epidemiological surveillance, intensive mosquito management programs, and public awareness campaigns about personal protective measures are crucial to the prevention of WNV transmission.

Acute and Delayed Deaths after West Nile Virus Infection, Texas, USA, 2002-2012

Infected patients should be closely monitored for prevention of future health problems.

Infection with West Nile virus (WNV) has a well-characterized acute disease process. However, long-term consequences are less understood. We searched death records for 4,142 residents of Texas, USA, infected with WNV during 2002–2012 and identified 557 (13%) deaths. We analyzed all-cause and cause-specific deaths after WNV infection by calculating standardized mortality ratios and using statewide mortality data. Acute-phase deaths (<90 days after symptom onset) occurred in 289 (7%) of case-patients; of those deaths, 289 (92%) were cases of West Nile neuroinvasive disease (WNND). Convalescent-phase deaths (>90 days after symptom onset) occurred in 268 (7%) of the remaining 3,853 case-patients; 210 (78%) of these deaths occurred in patients with WNND. Convalescent-phase WNND case-patients showed excess deaths from infectious and renal causes; case-patients <60 years of age had increased risk for all-cause death, specifically from renal, infectious, digestive, and circulatory causes. We provide population-level evidence of increased risk for death after WNV infection resulting in WNND.

Emergence and Associated Risk Factors of Vector Borne West Nile Virus Infection in Ilorin, Nigeria

BACKGROUND

West Nile Virus (WNV) is a mosquito-borne viral pathogen that is the causative agent of West Nile fever and encephalitis. Diagnostic tools for WNV infection in Nigeria are not well established hence the current prevalence rate of WNV infection in Nigeria is unknown. We aimed to establish the serological prevalence of WNV infection in febrile patients in Ilorin, Nigeria in 2016, and to assess the risk factors associated with the acquisition of the virus.

METHODS

This was a cross-sectional study involving the screening of subjects presenting with febrile illnesses. While specific IgM ELISA was used to determine the seroprevalence, a closed-ended questionnaire was used to ascertain the risk factors associated with this viral infection.

RESULTS

Fifteen (7.5%) of the respondents were positive for WNV infection. Subjects living in areas in close proximity to trees and bushes (P= 0.011) and stagnant water (P= 0.001) were at a higher risk of having WNV infection. Other risk factors associated with WNV among the respondents include the none use of insecticide (P= 0.001), sitting out at night (P= 0.044), HIV positivity (P= 0.003) and having an organ transplant (P= 0.002).

CONCLUSION

This study clearly shows a considerable WNV infection in Ilorin, with the presence of factors that can promulgate an outbreak, hence a need for further surveillance in the study area.

Prevalence of chronic comorbidities in dengue fever and West Nile virus: A systematic review and meta-analysis

Background

Flavivirus diseases such as dengue fever (DENV), West Nile virus (WNV), Zika and yellow fever represent a substantial global public health concern. Preexisting chronic conditions such as cardiovascular diseases, diabetes, obesity, and asthma were thought to predict risk of progression to severe infections.

Objective

We aimed to quantify the frequency of chronic comorbidities in flavivirus diseases to provide an estimate for their prevalence in severe and non-severe infections and examine whether chronic diseases contribute to the increased risk of severe viral expression.

Methods

We conducted a comprehensive search in PubMed, Ovid MEDLINE(R), Embase and Embase Classic and grey literature databases to identify studies reporting prevalence estimates of comorbidities in flavivirus diseases. Study quality was assessed with the risk of bias tool. Age-adjusted odds ratios (ORs) were estimated for severe infection in the presence of chronic comorbidities.

Results

We identified 65 studies as eligible for inclusion for DENV (47 studies) and WNV (18 studies). Obesity and overweight (i.e., BMI> 25 kg/m², prevalence: 24.5%, 95% CI: 18.6–31.6%), hypertension (17.1%, 13.3–21.8%) and diabetes (13.3%, 9.3–18.8%) were the most prevalent comorbidities in DENV. However, hypertension (45.0%, 39.1–51.0%), diabetes (24.7%, 20.2–29.8%) and heart diseases (25.6%, 19.5–32.7%) were the most prevalent in WNV. ORs of severe flavivirus diseases were about 2 to 4 in infected patients with comorbidities such as diabetes, hypertension and heart diseases. The small number of studies in JEV, YFV and Zika did not permit estimating the prevalence of comorbidities in these infections.

Conclusion

Higher prevalence of chronic comorbidities was found in severe cases of flavivirus diseases compared to non-severe cases. Findings of the present study may guide public health practitioners and clinicians to evaluate infection severity based on the presence of comorbidity, a critical public health measure that may avert severe disease outcome given the current dearth of clear prevention practices for some flavivirus diseases.

A disconnect between precursor frequency, expansion potential, and site-specific CD4+ T cell responses in aged mice

T cell recognition of peptides presented within self-major histocompatibility complex (pMHC) molecules is essential for long-lived protective immunity. As mice age the number of naïve CD4+ and CD8+ T cells declines. However, unlike for CD8+ T cells, there are more naïve and memory phenotype CD4+ T cells that bind foreign pMHCII in old mice (18-22 months) than adults (12-15 weeks), suggesting increased promiscuity of pMHCII recognition with aging. Here we asked if CD4+ T cell responses to immunization or infection increase with aging since the magnitude of a CD4+ T cell response to a foreign pMHCII is proportional to the size of the precursor population in adult mice. We observed no difference in the number of pMHCII-specific CD4+ T cells in adult versus old mice for pooled secondary lymphoid organs after immunization, bacterial infection, or viral infection, but we did observe diminished numbers of pMHCII-specific CD4+ T cells in both the draining lymph node and brain of old mice after West Nile virus infection. These data indicate that an increased precursor frequency does not translate into more robust responses upon immunization or infection in old mice.

Dynamics of Tissue-Specific CD8+ T Cell Responses during West Nile Virus Infection

The mouse model of West Nile virus (WNV), which is a leading cause of mosquito-borne encephalitis worldwide, has provided fundamental insights into the host and viral factors that regulate viral pathogenesis and infection outcome. In particular, CD8⁺ T cells are critical for controlling WNV replication and promoting protection against infection. Here, we present the characterization of a T cell receptor (TCR)-transgenic mouse with specificity for the immunodominant epitope in the WNV NS4B protein (here referred to as transgenic WNV-I mice). Using an adoptive-transfer model, we found that WNV-I CD8⁺ T cells behave similarly to endogenous CD8⁺ T cell responses, with an expansion phase in the periphery beginning around day 7 postinfection (p.i.) followed by a contraction phase through day 15 p.i. Through the use of in vivo intravascular immune cell staining, we determined the kinetics, expansion, and differentiation into effector and memory subsets of WNV-I CD8⁺ T cells within the spleen and brain. We found that red-pulp WNV-I CD8⁺ T cells were more effector-like than white-pulp WNV-I CD8⁺ T cells, which displayed increased differentiation into memory precursor cells. Within the central nervous system (CNS), we found that WNV-I CD8⁺ T cells were polyfunctional (gamma interferon [IFN-γ] and tumor necrosis factor alpha [TNF-α]), displayed tissue-resident characteristics (CD69⁺ and CD103⁺), persisted in the brain through day 15 p.i., and reduced the viral burden within the brain. The use of these TCR-transgenic WNV-I mice provides a new resource to dissect the immunological mechanisms of CD8⁺ T cell-mediated protection during WNV infection.IMPORTANCE West Nile Virus (WNV) is the leading cause of mosquito-borne encephalitis worldwide. There are currently no approved therapeutics or vaccines for use in humans to treat or prevent WNV infection. CD8⁺ T cells are critical for controlling WNV replication and protecting against infection. Here, we present a comprehensive characterization of a novel TCR-transgenic mouse with specificity for the immunodominant epitope in the WNV NS4B protein. In this study, we determine the kinetics, proliferation, differentiation into effector and memory subsets, homing, and clearance of WNV in the CNS. Our findings provide a new resource to dissect the immunological mechanisms of CD8⁺ T cell-mediated protection during WNV infection.

Taking a bite out of nutrition and arbovirus infection

Nutrition is a key factor in host–pathogen defense. Malnutrition can increase both host susceptibility and severity of infection through a number of pathways, and infection itself can promote nutritional deterioration and further susceptibility. Nutritional status can also strongly influence response to vaccination or therapeutic pharmaceuticals. Arthropod-borne viruses (arboviruses) have a long history of infecting humans, resulting in regular pandemics as well as an increasing frequency of autochthonous transmission. Interestingly, aside from host-related factors, nutrition could also play a role in the competence of vectors required for transmission of these viruses. Nutritional status of the host and vector could even influence viral evolution itself. Therefore, it is vital to understand the role of nutrition in the arbovirus lifecycle. This Review will focus on nutritional factors that could influence susceptibility and severity of infection in the host, response to prophylactic and therapeutic strategies, vector competence, and viral evolution.

As the old adage goes, you are what you eat. Proper nutrition is a cornerstone of health, and malnutrition can seriously impair the function of the immune system, resulting in increased infections or a more severe disease. Imbalanced or inadequate nutrition can also affect responses to vaccines or drugs that are vital for protection and treatment against viruses. A mosquito is also a product of what it eats. Nutrition during development and adult lifecycle can affect the feeding behavior of mosquitoes, thereby affecting transmission of viral diseases. Arthropod-borne viruses (arboviruses) are a major global health concern, especially in areas impacted by malnutrition. Understanding how nutrition can affect both humans and mosquitoes in the context of these viruses is vital to combating these diseases.

Morbidity, mortality and long-term sequelae of West Nile virus disease in Québec

We aimed to describe the clinical characteristics of West Nile patients reported in Québec in 2012 and 2013 and to document physical, mental and functional status 24 months after symptom onset according to illness severity. The cases were recruited by a public health professional. Data were collected from public health files, medical records and two standardised phone questionnaires: the Short Form-36 and the Instrumental Activities of Daily Living. In all, 92 persons participated in the study (25 had West Nile fever (WNF), 18 had meningitis and 49 had encephalitis). Encephalitis participants were older, had more underlying medical conditions, more neurological symptoms, worse hospital course and higher lethality than meningitis or WNF participants. Nearly half of the surviving hospitalised encephalitis patients required extra support upon discharge. At 24-month follow-up, encephalitis and meningitis patients had a lower score in two domains of the mental component: mental health and social functioning (P = 0.0025 and 0.0297, respectively) compared with the norms based on age- and sex-matched Canadians. Physical status was not affected by West Nile virus (WNV) infection. In addition, 5/36 (15%) of encephalitis, 1/17 (6%) of meningitis and 1/23 (5%) of WNF participants had new functional limitations 24 months after symptom onset. In summary, mental and functional sequelae in encephalitis patients are likely to represent a source of long-term morbidity. Preventive measures should target patients at higher risk of severe illness after WNV infection.

Understanding Knowledge, Attitudes, and Behaviors Toward West Nile Virus Prevention: A Survey of High-Risk Adults in Maryland

OBJECTIVE

To assess knowledge, attitudes, and behaviors toward West Nile virus (WNV) prevention among Maryland adults ≥60 years old who are at increased risk of severe WNV disease utilizing the health belief model.

METHODS

Using a stratified random sample of households from zip codes with ≥2 human WNV cases, we conducted a telephone survey of 211 Maryland adults ≥60 years old between October and December 2012.

RESULTS

Participants expressing worry about WNV were over thrice more likely to use insect repellent in the prior 90 days (adjusted odds ratio [aOR] = 3.46, 95% confidence interval [CI] = 1.33-8.95) and nearly thrice more likely to drain standing water around their homes than those not worried (aOR = 2.86, 95% CI = 1.25-6.52). Respondents perceiving a benefit in paying less for WNV vaccine were more likely to support mosquito control programs (aOR = 16.00, 95% CI = 1.50-170.68).

CONCLUSIONS

Future interventions to promote WNV prevention among older adults should seek to enhance perceptions of vulnerability to WNV through risk communication, including media outreach and written messaging, emphasizing the benefits of personal protective behaviors. Community partnerships may aid in outreach to this population.

Epidemiologic and clinical parameters of West Nile virus infections in humans: a scoping review

Background

Clinical syndromes associated with West Nile virus (WNV) infection range from fever to neuroinvasive disease. Understanding WNV epidemiology and disease history is important for guiding patient care and healthcare decision-making. The objective of this review was to characterize the existing body of peer-reviewed and surveillance literature on WNV syndromes and summarize epidemiologic and clinical parameters.

Methods

We followed scoping review methodology described by the Joanna Briggs Institute. Terms related to WNV epidemiology, hospitalization, and surveillance were searched in four bibliographic databases (MEDLINE, EMBASE, Scopus, and CINAHL) for literature published from January 1999 to December 2015.

Results

In total, 2334 non-duplicated titles and abstracts were screened; 92 primary studies were included in the review. Publications included one randomized controlled trial and 91 observational studies. Sample sizes ranged from under 25 patients (n = 19) to over 400 patients (n = 28). Eight studies were from Canada, seven from Israel, and the remaining (n = 77) from the United States. N = 17 studies were classified as outbreak case investigations following epidemics; n = 37 with results of regional/national surveillance and monitoring programs.

Mean patient ages were > 40 years old; three studies (3%) focused on the pediatric population. Patients with encephalitis fared worse than patients with meningitis and fever, considering hospitalization, length of stay, discharge, recovery, and case-fatality. Several studies examined risk factors; however, age was the only risk factor for neuroinvasive disease/death consistently identified. Overall, patients with acute flaccid paralysis or encephalitis fared worse than patients with meningitis and West Nile fever in terms of hospitalization and mortality. Among the included studies, proportion hospitalized, length of stay, proportion discharged home and case-fatality ranged considerably.

Conclusion

Our review highlights the heterogeneity among reporting clinical WNV syndromes and epidemiologic parameters of WNV-related illness. Presently, there is potential for further synthesis of the risk factors of WNV-illness and mortality; undertaking further analysis through a systematic review and meta-analysis may benefit our understanding of risk factors for emerging mosquito-borne diseases. Future research on the burden of WNV can build on existing evidence summarized in this review, not only to support our understanding of endemic WNV, but also to strengthen research on emerging arboviruses with similar clinical manifestations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2637-9) contains supplementary material, which is available to authorized users.

West Nile Virus Infection

Although long recognized as a human pathogen, West Nile virus (WNV) emerged as a significant public health problem following its introduction and spread across North America. Subsequent years have seen a greater understanding of all aspects of this viral infection. The North American epidemic resulted in a further understanding of the virology, pathogenesis, clinical features, and epidemiology of WNV infection. Approximately 80% of human WNV infections are asymptomatic. Most symptomatic people experience an acute systemic febrile illness; less than 1% of infected people develop neuroinvasive disease, which typically manifests as meningitis, encephalitis, or anterior myelitis resulting in acute flaccid paralysis. Older age is associated with more severe illness and higher mortality; other risk factors for poor outcome have been challenging to identify. In addition to natural infection through mosquito bites, transfusion- and organ transplant-associated infections have occurred. Since there is no definitive treatment for WNV infection, protection from mosquito bites and other preventative measures are critical. WNV has reached an endemic pattern in North America, but the future epidemiologic pattern is uncertain.

Age-related alterations in immune responses to West Nile virus infection

West Nile virus (WNV) is the most important causative agent of viral encephalitis worldwide and an important public health concern in the United States due to its high prevalence, severe disease, and the absence of effective treatments. Infection with WNV is mainly asymptomatic, but some individuals develop severe, possibly fatal, neurological disease. Individual host factors play a role in susceptibility to WNV infection, including genetic polymorphisms in key anti-viral immune genes, but age is the most well-defined risk factor for susceptibility to severe disease. Ageing is associated with distinct changes in immune cells and a decline in immune function leading to increased susceptibility to infection and reduced responses to vaccination. WNV is detected by pathogen recognition receptors including Toll-like receptors (TLRs), which show reduced expression and function in ageing. Neutrophils, monocyte/macrophages and dendritic cells, which first recognize and respond to infection, show age-related impairment of many functions relevant to anti-viral responses. Natural killer cells control many viral infections and show age-related changes in phenotype and functional responses. A role for the regulatory receptors Mertk and Axl in blood-brain barrier permeability and in facilitating viral uptake through phospholipid binding may be relevant for susceptibility to WNV, and age-related up-regulation of Axl has been noted previously in human dendritic cells. Understanding the specific immune parameters and mechanisms that influence susceptibility to symptomatic WNV may lead to a better understanding of increased susceptibility in elderly individuals and identify potential avenues for therapeutic approaches: an especially relevant goal, as the world's populating is ageing.

Acute systemic DNA damage in youth does not impair immune defense with aging

Aging‐related decline in immunity is believed to be the main driver behind decreased vaccine efficacy and reduced resistance to infections in older adults. Unrepaired DNA damage is known to precipitate cellular senescence, which was hypothesized to be the underlying cause of certain age‐related phenotypes. Consistent with this, some hallmarks of immune aging were more prevalent in individuals exposed to whole‐body irradiation (WBI), which leaves no anatomical repository of undamaged hematopoietic cells. To decisively test whether and to what extent WBI in youth will leave a mark on the immune system as it ages, we exposed young male C57BL/6 mice to sublethal WBI (0.5–4 Gy), mimicking human survivor exposure during nuclear catastrophe. We followed lymphocyte homeostasis thorough the lifespan, response to vaccination, and ability to resist lethal viral challenge in the old age. None of the irradiated groups showed significant differences compared with mock‐irradiated (0 Gy) animals for the parameters measured. Even the mice that received the highest dose of sublethal WBI in youth (4 Gy) exhibited equilibrated lymphocyte homeostasis, robust T‐ and B‐cell responses to live attenuated West Nile virus (WNV) vaccine and full survival following vaccination upon lethal WNV challenge. Therefore, a single dose of nonlethal WBI in youth, resulting in widespread DNA damage and repopulation stress in hematopoietic cells, leaves no significant trace of increased immune aging in a lethal vaccine challenge model.

Encephalitic Arboviruses: Emergence, Clinical Presentation, and Neuropathogenesis

Arboviruses are arthropod-borne viruses that exhibit worldwide distribution, contributing to systemic and neurologic infections in a variety of geographical locations. Arboviruses are transmitted to vertebral hosts during blood feedings by mosquitoes, ticks, biting flies, mites, and nits. While the majority of arboviral infections do not lead to neuroinvasive forms of disease, they are among the most severe infectious risks to the health of the human central nervous system. The neurologic diseases caused by arboviruses include meningitis, encephalitis, myelitis, encephalomyelitis, neuritis, and myositis in which virus- and immune-mediated injury may lead to severe, persisting neurologic deficits or death. Here we will review the major families of emerging arboviruses that cause neurologic infections, their neuropathogenesis and host neuroimmunologic responses, and current strategies for treatment and prevention of neurologic infections they cause.

Zoonotic and Vector-Borne Infections Among Urban Homeless and Marginalized People in the United States and Europe, 1990-2014

INTRODUCTION

In high-income countries, homeless individuals in urban areas often live in crowded conditions with limited sanitation and personal hygiene. The environment of homelessness in high-income countries may result in intensified exposure to ectoparasites and urban wildlife, which can transmit infections. To date, there have been no systematic evaluations of the published literature to assess vector-borne and zoonotic disease risk to these populations.

OBJECTIVES

The primary objectives of this study were to identify diversity, prevalence, and risk factors for vector-borne and zoonotic infections among people experiencing homelessness and extreme poverty in urban areas of high-income countries.

METHODS

We conducted a systematic review and narrative synthesis of published epidemiologic studies of zoonotic and vector-borne infections among urban homeless and very poor people in the United States and Europe from 1990 to 2014.

RESULTS

Thirty-one observational studies and 14 case studies were identified (n = 45). Seroprevalence to the human louse-borne pathogen Bartonella quintana (seroprevalence range: 0-37.5%) was identified most frequently, with clinical disease specifically observed among HIV-positive individuals. Seropositivity to Bartonella henselae (range: 0-10.3%) and Rickettsia akari (range: 0-16.2%) was noted in multiple studies. Serological evidence of exposure to Rickettsia typhi, Rickettsia prowazekii, Bartonella elizabethae, West Nile virus, Borellia recurrentis, lymphocytic choriomeningitis virus, Wohlfartiimonas chitiniclastica, Seoul hantavirus (SEOV), and Leptospira species was also identified in published studies, with SEOV associated with chronic renal disease later in life. HIV infection, injection drug use, and heavy drinking were noted across multiple studies as risk factors for infection with vector-borne and zoonotic pathogens.

CONCLUSIONS

B. quintana was the most frequently reported vector-borne infection identified in our article. Delousing efforts and active surveillance among HIV-positive individuals, who are at elevated risk of complication from B. quintana infection, are advised to reduce morbidity. Given documented exposure to rodent-borne zoonoses among urban homeless and marginalized people, reducing human contact with rodents remains an important public health priority.

West Nile Virus Retinopathy and Associations with Long Term Neurological and Neurocognitive Sequelae

West Nile virus (WNV) has emerged as an important vector-borne pathogen in North America, with more than 3 million estimated to have been infected. Retinopathy from WNV infection has been previously reported in acute cases, though those prior reports did not evaluate the risk of retinopathy based on clinical severity of neurologic disease. The purpose of this cross-sectional study was to perform comprehensive ophthalmological and neurological examinations on 111 patients with a history of West Nile virus infection and describe the ocular manifestations. Out of 111 patients, 27 (24%) had evidence for West Nile virus associated retinopathy (WNVR); this observation was higher (49%) in those patients who initially presented with encephalitis. Individuals with WNVR had more frequent involvement of the macula and peripheral involvement compared to those patients without WNVR (p<0.05). WNVR was also associated with a greater likelihood of abnormal reflexes on neurological exam, poorer learning, greater dependence in activities of daily living, and lower quality of life (p<0.05). WNVR was seen more frequently in elderly patients (age > 60 years), and was associated with higher rates of diabetes mellitus and a history of encephalitis (p<0.05). A multivariable logistic regression revealed that only a history of encephalitis was independently associated with WNVR [Adjusted Odds Ratio = 4.9 (1.8–13.2); p = 0.001]. Our study found that WNVR occurs in one fourth of patients with a history of WNV infection and is more frequently observed in those with apparent severe neurological sequelae (e.g., encephalitis). The clinical relevance of WNVR was supported by its associations with dependence in activities of daily living and lower quality of life. This unique evaluation of WNV patients included fundoscopic examinations and their associations with neurologic impairment. Our findings can be used during ophthalmological consultation for the evaluation, treatment and rehabilitation phases of care for WNV patients.

Flaviviruses as a Cause of Undifferentiated Fever in Sindh Province, Pakistan: A Preliminary Report

Arboviral diseases are expanding worldwide, yet global surveillance is often limited due to diplomatic and cultural barriers between nations. With human encroachment into new habitats, mosquito-borne viruses are also invading new areas. The actual prevalence of expanding arboviruses is unknown in Pakistan due to inappropriate diagnosis and poor testing for arboviral diseases. The primary objective of this study was to document evidence of flavivirus infections as the cause of undifferentiated fever in Pakistan. Through a cooperative effort between the USA and Pakistan, patient exposure to dengue virus (DENV), West Nile virus (WNV), and Japanese encephalitis virus (JEV) was examined in Sindh Province for the first time in decades. Initial results from the 2015 arbovirus season consisting of a cross-sectional study of 467 patients in 5 sites, DENV NS1 antigen was identified in 63 of the screened subjects, WNV IgM antibodies in 16 patients, and JEV IgM antibodies in 32 patients. In addition, a number of practical findings were made including (1) in silico optimization of RT-PCR primers for flavivirus strains circulating in the Middle East, (2) shipping and storage of RT-PCR master mix and other reagents at ambient temperature, (3) Smart phone applications for the collection of data in areas with limited infrastructure, and (4) fast and reliable shipping for transport of reagents and specimens to and from the Middle East. Furthermore, this work is producing a group of highly trained local scientists and medical professionals disseminating modern scientific methods and more accurate diagnostic procedures to the community.

West Nile virus infection in children

West Nile virus (WNV) is an emerging flavivirus responsible for an increasing number of outbreaks of neuroinvasive disease in North America, Europe, and neighboring countries. Almost all WNV infections in humans are transmitted through the bite of infected mosquitoes. Transmission during pregnancy and through breastfeeding has been reported, but the risk seems to be very low. West Nile disease in children is less common (1-5% of all WNV cases) and associated with milder symptoms and better outcome than in elderly individuals, even though severe neuroinvasive disease and death have been reported also among children. However, the incidence of WNV infection and disease in children is probably underestimated and the disease spectrum is not fully understood because of lack of reporting and underdiagnosis in children. Infection is diagnosed by detection of WNV-specific antibodies in serum and WNV RNA in plasma and urine. Since no effective WNV-specific drugs are available, therapy is mainly supportive.

Long-term sequelae of West Nile virus-related illness: a systematic review

We systematically reviewed the clinical outlook of West Nile virus (WNV)-related illness in North America and western Europe. As of March, 2015, more than 45 000 cases of WNV-related illness have been reported in North America. Unlike acute morbidity and mortality, the long-term physical, cognitive, and functional sequelae associated with WNV-related illness are not well characterised. An understanding of WNV-related sequelae and their prognostic factors can support physicians with early diagnosis and tertiary prevention efforts. We searched Ovid Medline, Embase, Scopus, and Environment Complete for studies published between 1999 and 2015. We included 67 studies in our Review. Although muscle weakness, memory loss, and difficulties with activities of daily living were among the most common physical, cognitive, and functional sequelae, respectively, some population groups were reported to be at greater risk of severe neurological disease or death (ie, older men with underlying illnesses such as cardiovascular disease or cancer). A high level of heterogeneity was reported among studies included in this Review, suggesting a need for consistent methods for collecting data and reporting findings. Further, more than half of the studies reporting sequelae relied exclusively on subjective assessment and only two studies used matched control groups. Therefore, opportunities exist for more robust primary studies in future research.

Long-term neurological outcomes in West Nile virus-infected patients: an observational study

The Houston West Nile Cohort (HWNC) was founded in 2002 when West Nile virus (WNV) reached Houston, TX. The long-term outcomes following WNV infection are still mostly unknown, though neurological abnormalities up to 1 year postinfection have been documented. We report an observational study of neurological abnormalities at 1-3 and 8-11 years following WNV infection in the HWNC. We conducted standard neurological examinations at two separate time points to assess changes in neurological status over time. The majority of patients (86%, 30/35) with encephalitis had abnormal neurological exam findings at the time of the first assessment compared with uncomplicated fever (27%, 3/11) and meningitis (36%, 5/14) cases. At the time of the second assessment, 57% (4/7) of West Nile fever (WNF), 33% (2/6) of West Nile meningitis (WNM), and 36% (5/14) of West Nile encephalitis (WNE) had developed new neurological complications. The most common abnormalities noted were tandem gait, hearing loss, abnormal reflexes, and muscle weakness. Long-term neurological abnormalities were most commonly found in patients who experienced primary WNV encephalitis. New abnormalities may develop over time regardless of initial clinical infection. Future studies should aim to differentiate neurological consequences due to WNV neuroinvasive infection versus neurological decline related to comorbid conditions.

Risk factors for West Nile virus infection and disease in populations and individuals

West Nile virus (WNV) is a mosquito-borne enveloped positive-strand RNA virus that emerged in North America in 1999 in New York City. Over the past 15 years, WNV has become established throughout the USA and has spread into Canada, Mexico and the Caribbean. CDC reports indicate >41,000 clinical cases, including more than 1700 fatalities. An estimated 3 million people in the USA may have been infected to date. Infection with WNV is dependent on many factors including climate, mosquito habitats and immunologically naïve bird populations. In addition, variations within individuals contribute to the risk of severe disease, in particular, advanced age, hypertension, immunosuppression and critical elements of the immune response. Recent advances in technology now allow detailed analysis of complex immune interactions relevant to disease susceptibility.

Anti-inflammatory activity of intravenous immunoglobulins protects against West Nile virus encephalitis

West Nile virus (WNV), an important global human pathogen, targets neurons to cause lethal encephalitis, primarily in elderly and immunocompromised patients. Currently, there are no approved therapeutic agents or vaccines to treat WNV encephalitis. Recent studies have suggested that inflammation is a major contributor to WNV encephalitis morbidity. In this study we evaluated the use of IVIG (intravenous immunoglobulins - a clinical product comprising pooled human IgG) as an anti-inflammatory treatment in a model of lethal WNV infection. We report here that IVIG and pooled human WNV convalescent sera (WNV-IVIG) inhibited development of lethal WNV encephalitis by suppressing central nervous system (CNS) infiltration by CD45(high) leukocytes. Pathogenic Ly6C(high) CD11b(+) monocytes were the major infiltrating subset in the CNS of infected control mice, whereas IVIG profoundly reduced infiltration of these pathogenic Ly6C(high) monocytes into the CNS of infected mice. Interestingly, WNV-IVIG was more efficacious than IVIG in controlling CNS inflammation when mice were challenged with a high-dose inoculum (10(5) versus 10(4) p.f.u.) of WNV. Importantly, adsorption of WNV E-glycoprotein neutralizing antibodies did not abrogate IVIG protection, consistent with virus neutralization not being essential for IVIG protection. These findings confirmed the potent immunomodulatory activity of generic IVIG, and emphasized its potential as an effective immunotherapeutic drug for encephalitis and other virus induced inflammatory diseases.

An outbreak of West Nile Virus infection in the region of Monastir, Tunisia, 2003

BACKGROUND

A West Nile (WN) fever epidemic occurred in the region of Monastir, Tunisia, between August and October 2003.

AIM OF THE STUDY

We attempt to describe the epidemiology, clinical presentation, and outcome of patients with confirmed West Nile virus (WNV) infection.

METHODS

Three groups of specimens were prepared. One was made up of serum only (n  =  43), the other of cerebrospinal fluid (CSF) only (n  =  30), and the third group was made up of both (n  =  40). These specimens were obtained from 113 patients. A serological diagnosis and evidence of WNV genome by nested reverse-transcriptase polymerase chain reaction (nRT-PCR) and TaqMan reverse transcription-polymerase chain reaction (RT-PCR) were carried out.

RESULTS

Thirty-eight cases (33.6%) were serologically positive. Results of nRT-PCR showed a total of 10 positive cases of WNV (8.8%) detected in group 1 (n  =  1/43), group 2 (n  =  5/30), and group 3 (n  =  4/40) whereas the PCR TaqMan showed 18 positive samples (15.9%) found in group 1 (n  =  3/43), group 2 (n  =  9/30), and group 3 (n  =  6/40). All TaqMan PCR positive cases were nRT-PCR positive. In addition, four serologically probable cases were confirmed by TaqMan PCR. The attempts to isolate WNV by cell culture were unsuccessful. Considering the results of TaqMan assay and the serological diagnosis, WNV infection was confirmed in a total of 42 patients. The main clinical presentations were meningoencephalitis (40%), febrile disease (95%), and meningitis (36%). Eight patients (19%) died. The highest case-fatality rates occurred among patients aged ≧55 years. The phylogenetic analysis revealed that isolates of WNV were closely related to the Tunisian strain 1997 (PAH001) and the Israeli one (Is-98).

CONCLUSIONS

West Nile virus is a reemerging global pathogen that remains an important public health challenge in the next decade.

West nile virus and equine encephalitis viruses: new perspectives

Mosquito-borne diseases affect horses worldwide. Mosquito-borne diseases generally cause encephalomyelitis in the horse and can be difficult to diagnose antemortem. In addition to general disease, and diagnostic and treatment aspects, this review article summarizes the latest information on these diseases, covering approximately the past 5 years, with a focus on new equine disease encroachments, diagnostic and vaccination aspects, and possible therapeutics on the horizon.