Fatal Powassan Encephalitis (Deer Tick Virus, Lineage II) in a Patient With Fever and Orchitis Receiving Rituximab

Age-dependent Powassan virus lethality is linked to glial cell activation and divergent neuroinflammatory cytokine responses in a murine model

Powassan virus (POWV) is an emergent tick-borne flavivirus that causes fatal encephalitis in the elderly and long-term neurologic sequelae in survivors. How age contributes to severe POWV encephalitis remains an enigma, and no animal models have assessed age-dependent POWV neuropathology. Inoculating C57BL/6 mice with a POWV strain (LI9) currently circulating in Ixodes ticks resulted in age-dependent POWV lethality 10-20 dpi. POWV infection of 50-week-old mice was 82% fatal with lethality sequentially reduced by age to 7.1% in 10-week-old mice. POWV LI9 was neuroinvasive in mice of all ages, causing acute spongiform CNS pathology and reactive gliosis 5-15 dpi that persisted in survivors 30 dpi. High CNS viral loads were found in all mice 10 dpi. However, by 15 dpi, viral loads decreased by 2-4 logs in 10- to 40-week-old mice, while remaining at high levels in 50-week-old mice. Age-dependent differences in CNS viral loads 15 dpi occurred concomitantly with striking changes in CNS cytokine responses. In the CNS of 50-week-old mice, POWV induced Th1-type cytokines (IFNγ, IL-2, IL-12, IL-4, TNFα, IL-6), suggesting a neurodegenerative pro-inflammatory M1 microglial program. By contrast, in 10-week-old mice, POWV-induced Th2-type cytokines (IL-10, TGFβ, IL-4) were consistent with a neuroprotective M2 microglial phenotype. These findings correlate age-dependent CNS cytokine responses and viral loads with POWV lethality and suggest potential neuroinflammatory therapeutic targets. Our results establish the age-dependent lethality of POWV in a murine model that mirrors human POWV severity and long-term CNS pathology in the elderly.

IMPORTANCE

Powassan virus is an emerging tick-borne flavivirus causing lethal encephalitis in aged individuals. We reveal an age-dependent POWV murine model that mirrors human POWV encephalitis and long-term CNS damage in the elderly. We found that POWV is neuroinvasive and directs reactive gliosis in all age mice, but at acute stages selectively induces pro-inflammatory Th1 cytokine responses in 50-week-old mice and neuroprotective Th2 cytokine responses in 10-week-old mice. Our findings associate CNS viral loads and divergent cytokine responses with age-dependent POWV lethality and survival outcomes. Responses of young mice suggest potential therapeutic targets and approaches for preventing severe POWV encephalitis that may be broadly applicable to other neurodegenerative diseases. Our age-dependent murine POWV model permits analysis of vaccines that prevent POWV lethality, and therapeutics that resolve severe POWV encephalitis.

Laboratory Testing for Powassan Virus: Past, Present, and Future

Powassan virus is a tick-borne flavivirus that can cause severe neuroinvasive disease, with areas of endemicity in the Northeast and Midwest United States, Canada, and Russia. Diagnosis is challenging and relies on a high index of suspicion and choosing the right test based on duration of infection and the patient's immune status. This review covers laboratory testing for Powassan virus, including historical considerations, modern options, and methods being developed in the research space.

Comparative Pathogenesis of Two Lineages of Powassan Virus Reveals Distinct Clinical Outcome, Neuropathology, and Inflammation

Tick-borne flaviviruses (TBFV) can cause severe neuroinvasive disease which may result in death or long-term neurological deficit in over 50% of survivors. Multiple mechanisms for invasion of the central nervous system (CNS) by flaviviruses have been proposed including axonal transport, transcytosis, endothelial infection, and Trojan horse routes. Flaviviruses may utilize different or multiple mechanisms of neuroinvasion depending on the specific virus, infection site, and host variability. In this work we have shown that the infection of BALB/cJ mice with either Powassan virus lineage I (Powassan virus) or lineage II (deer tick virus) results in distinct spatial tropism of infection in the CNS which correlates with unique clinical presentations for each lineage. Comparative transcriptomics of infected brains demonstrates the activation of different immune pathways and downstream host responses. Ultimately, the comparative pathology and transcriptomics are congruent with different clinical signs in a murine model. These results suggest that the different disease presentations occur in clinical cases due to the inherent differences in the two lineages of Powassan virus.

Diagnostic yield of postmortem brain examination following premortem brain biopsy for neoplastic and nonneoplastic disease

Medical autopsies have decreased in frequency due in part to advances in radiological techniques and increased availability of molecular and other ancillary testing. However, premortem diagnosis of CNS disease remains challenging; while ∼90% of brain tumor biopsies are diagnostic, only 20%-70% of biopsies for presumed nonneoplastic disease result in a specific diagnosis. The added benefits of performing an autopsy following surgical brain biopsy are not well defined. A retrospective analysis was performed of patients who underwent brain biopsy and autopsy at Brigham and Women's Hospital from 2003 to 2022. A total of 135 cases were identified, including 95 (70%) patients with primary CNS neoplasms, 16 (12%) with metastatic tumors, and 24 (18%) with nonneoplastic neurological disease. Diagnostic concordance between biopsy and autopsy diagnosis was excellent both for primary CNS neoplasms (98%) and metastatic tumors (94%). Conversely, patients with nonneoplastic disease received definitive premortem diagnoses in 7/24 (29%) cases. Five (21%) additional patients received conclusive diagnoses following autopsy; 8 (33%) received a more specific differential diagnosis compared to the biopsy. Overall, autopsy confirmed premortem diagnoses or provided new diagnostic information in 131/135 (97%) cases, highlighting the value in performing postmortem brain examination in patients with both neoplastic and nonneoplastic diseases.

A comprehensive neurological perspective on tick-borne flaviviruses, with emphasis on Powassan virus

Powassan virus (POWV), a tick-borne flavivirus transmitted primarily by Ixodes ticks, poses a significant threat as it can lead to severe neuroinvasive illness. This review delves into the nuanced clinical presentation of Powassan infection, a challenge in diagnosis exacerbated by the absence of an available vaccine. Over the past decade, the prevalence of POWV has surged in North America, necessitating a thorough examination of its neurological manifestations alongside tick-borne encephalitis virus (TBEV). A comprehensive literature search conducted up to January 2024 revealed 135 cases of neurological symptoms associated with either Powassan or TBEV infection. Notably, severe occipital headache emerged as the most prevalent symptom (22.75%), followed by meningoencephalitis (10.34%), seizures (8.27%), and flaccid paresis (6.8%). Additional manifestations included poor balance, wide gait, dysarthria, facial nerve palsy, seizure, slurred speech, and absent deep tendon reflexes. Tragically, nine cases resulted in fatal outcomes attributed to POWV infection. This analysis highlights the intricate spectrum of neurological symptoms associated with Powassan infection and underscores the necessity for heightened awareness among medical practitioners, particularly in regions with a higher prevalence of the virus. The complexity of symptoms emphasizes the need for further research to unravel the factors contributing to this diversity. Additionally, exploring potential treatment avenues and vaccine development is crucial in addressing the rising threat posed by POWV, ultimately enhancing our ability to manage and prevent severe neurological outcomes.

Powassan Virus Infections: A Systematic Review of Published Cases

BACKGROUND

Powassan virus is an emerging neurotropic arbovirus transmitted by the tick Ixodes scapularis. This systematic review was conducted to aggregate data on its clinical manifestations, diagnostic findings, and complications.

METHODS

PubMed was searched until August 2023 using the term "Powassan", to identify all published cases of Powassan virus infections, as per PRISMA guidelines.

RESULTS

Among the 380 abstracts identified, 45 studies describing 84 cases (70 adult, 14 pediatric) were included. Cases were reported from the USA and Canada. Complications included paralysis in 44.1% of adult and 42.6% of pediatric cases, cognitive deficits in 33.3% of adult and 25% of pediatric cases, while the mortality rate was 19.1% and 7.1% in the adult and pediatric populations, respectively. Correlation analysis revealed an association between mortality and age (r = 0.264, p = 0.029), development of paralysis (r = 0.252, p = 0.041), or respiratory distress or failure (r = 0.328, p = 0.006). Factors associated with persistent neurological deficits were development of ataxia (r = 0.383, p = 0.006), paralysis (r = 0.278, p = 0.048), speech disorder (r = 0.319, p = 0.022), and cranial nerve involvement (r = 0.322, p = 0.017). Other significant correlations included those between speech disorders and ataxia (r = 0.526, p < 0.001), and between paralysis and respiratory distress or failure (r = 0.349, p = 0.003).

CONCLUSION

Powassan virus infections have significant morbidity and mortality and should be suspected in cases of encephalitis and possible tick exposure. PROSPERO registration number: CRD42023395991.

Of Murines and Humans: Modeling Persistent Powassan Disease in C57BL/6 Mice

Powassan infection is caused by two closely related, tick-transmitted viruses of the genus Flavivirus (family Flaviviridae): Powassan virus lineage I (POWV) and lineage II (known as deer tick virus [DTV]). Infection is typically asymptomatic or mild but can progress to neuroinvasive disease. Approximately 10% of neuroinvasive cases are fatal, and half of the survivors experience long-term neurological sequelae. Understanding how these viruses cause long-term symptoms as well as the possible role of viral persistence is important for developing therapies. We intraperitoneally inoculated 6-week-old C57BL/6 mice (50% female) with 103 focus-forming units (FFU) DTV and assayed for infectious virus, viral RNA, and inflammation during acute infection and 21, 56, and 84 days postinfection (dpi). Although most mice (86%) were viremic 3 dpi, only 21% of the mice were symptomatic and 83% recovered. Infectious virus was detected only in the brains of mice sampled during the acute infection. Viral RNA was detected in the brain until 84 dpi, but the magnitude decreased over time. Meningitis and encephalitis were visible in acute mice and from mice sampled at 21 dpi. Inflammation was observed until 56 dpi in the brain and 84 dpi in the spinal cord, albeit at low levels. These results suggest that the long-term neurological symptoms associated with Powassan disease are likely caused by lingering viral RNA and chronic inflammation in the central nervous system rather than by a persistent, active viral infection. The C57BL/6 model of persistent Powassan mimics illness in humans and can be used to study the mechanisms of chronic disease. IMPORTANCE Half of Powassan infection survivors experience long-term, mild to severe neurological symptoms. The progression from acute to chronic Powassan disease is not well understood, severely limiting treatment and prevention options. Infection of C57BL/6 mice with DTV mimics clinical disease in humans, and the mice exhibit CNS inflammation and viral RNA persistence until at least 86 dpi, while infectious virus is undetectable after 12 dpi. These findings suggest that the long-term neurological symptoms of chronic Powassan disease are in part due the persistence of viral RNA and the corresponding long-term inflammation of the brain and spinal cord. Our work demonstrates that C57BL/6 mice can be used to study the pathogenesis of chronic Powassan disease.

Severe Arboviral Neuroinvasive Disease in Patients on Rituximab Therapy: A Review

With increasing use of rituximab and other B-cell depleting monoclonal antibodies for multiple indications, infectious complications are being recognized. We summarize clinical findings of patients on rituximab with arboviral diseases identified through literature review or consultation with the Centers for Disease Control and Prevention. We identified 21 patients on recent rituximab therapy who were diagnosed with an arboviral disease caused by West Nile, tick-borne encephalitis, eastern equine encephalitis, Cache Valley, Jamestown Canyon, and Powassan viruses. All reported patients had neuroinvasive disease. The diagnosis of arboviral infection required molecular testing in 20 (95%) patients. Median illness duration was 36 days (range, 12 days to 1 year), and 15/19 (79%) patients died from their illness. Patients on rituximab with arboviral disease can have a severe or prolonged course with an absence of serologic response. Patients should be counseled about mosquito and tick bite prevention when receiving rituximab and other B-cell depleting therapies.

Dermatological manifestations of tick-borne viral infections found in the United States

Tick-borne diseases (TBDs) are bacterial, viral, and parasitic diseases transmitted by ticks. Viral TBDs have increased in prevalence over the last decade with many new pathogenic viruses being discovered. Doxycycline is often empirically prescribed by clinicians to treat symptomatic patients following tick bites due to suspicions of bacterial TBDs such as Rocky Mountain spotted fever, anaplasmosis, and ehrlichiosis. However, viral TBDs are included in the differential diagnosis if patients do not clinically improve following antibiotic therapy. Several viral TBDs present with dermatological manifestations. Recognizing the differences in clinical presentations of TBDs, particularly of newly emerging viral TBDs in the United States, can help physicians identify the viral TBD, and possibly rule out viral illnesses with different clinical presentations. Therefore, this review discusses clinical manifestations, with an emphasis on dermatologic manifestations of Heartland Virus, Bourbon Virus, Powassan Virus, Deer Tick Virus and Colorado Tick Fever Virus. KEY POINTS: Viral tick-borne diseases have increased in prevalence over the last decade and often have similar clinical manifestations to other tick-borne diseases, including bacterial infections. Here, we review the dermatologic manifestations of Heartland Virus (HRTV), Bourbon Virus (BRBV), Powassan Virus (POWV), Deer Tick Virus (DTV) and Colorado Tick Fever Virus (CTFV) that are important for clinicians.

B cells going viral in the CNS: Dynamics, complexities, and functions of B cells responding to viral encephalitis

A diverse number of DNA and RNA viruses have the potential to invade the central nervous system (CNS), causing inflammation and injury to cells that have a limited capacity for repair and regeneration. While rare, viral encephalitis in humans is often fatal and survivors commonly suffer from permanent neurological sequelae including seizures. Established treatment options are extremely limited, predominantly relying on vaccines, antivirals, or supportive care. Many viral CNS infections are characterized by the presence of antiviral antibodies in the cerebral spinal fluid (CSF), indicating local maintenance of protective antibody secreting cells. However, the mechanisms maintaining these humoral responses are poorly characterized. Furthermore, while both viral and autoimmune encephalitis are associated with the recruitment of diverse B cell subsets to the CNS, their protective and pathogenic roles aside from antibody production are just beginning to be understood. This review will focus on the relevance of B cell responses to viral CNS infections, with an emphasis on the importance of intrathecal immunity and the potential contribution to autoimmunity. Specifically, it will summarize the newest data characterizing B cell activation, differentiation, migration, and localization in clinical samples as well as experimental models of acute and persistent viral encephalitis.

Powassan Virus Encephalitis

Powassan virus is an increasingly recognized cause of severe encephalitis that is transmitted by Ixodes ticks. Given the nonspecific clinical, laboratory, and imaging features of Powassan virus disease, providers should consider it in patients with compatible exposures and request appropriate testing.

Laboratory Validation of a Real-Time RT-PCR Assay for the Detection of Jamestown Canyon Virus

The neuroinvasive disease caused by Jamestown Canyon virus (JCV) infection is rare. However, increasing incidence and widespread occurrence of the infection make JCV a growing public health concern. Presently, clinical diagnosis is achieved through serological testing, and mosquito pool surveillance requires virus isolation and identification. A rapid molecular detection test, such as real-time RT-PCR, for diagnosis and surveillance of JCV has not been widely utilized. To enhance testing and surveillance, here, we describe the development and validation of a real-time RT-PCR test for the detection of JCV RNA. Three primer and probe sets were evaluated for analytical sensitivity and specificity. One probe set, JCV132FAM, was found to be the most sensitive test detecting 7.2 genomic equivalents/µL. While less sensitive, a second probe set JCV231cFAM was the most specific test with limited detection of Keystone virus at high RNA loads. Taken together, these data indicate both probe sets can be utilized for a primary sensitive screening assay and a secondary specific confirmatory assay. While both primer and probe sets detected high viral loads of Keystone virus, these assays did not detect any virus in the California encephalitis virus clade, including negative detection of the medically important La Crosse virus (LACV) and snowshoe hare virus (SSHV). The real-time RT-PCR assay described herein could be utilized in diagnosis and surveillance in regions with co-circulation of JCV and LACV or SSHV to inform public health action.

Novel Applications of Metagenomics for Detection of Tickborne Pathogens

Background

Tick populations have expanded in many parts of the globe, bringing with them an enhanced appreciation and discovery of novel tickborne pathogens, as well an increased in reported human cases of tickborne disease. Targeted and unbiased (shotgun) clinical metagenomic sequencing tests are increasingly used for detection of known and emerging infectious agents and have recently been employed for detection of tickborne pathogens.

Content

This review describes the types of metagenomic sequencing assays used for detection of emerging tickborne pathogens and reviews the recent literature on this topic. Important diagnostic and interpretative challenges are also covered.

Summary

Metagenomic analysis has emerged as a powerful tool for detection, discovery, characterization, and classification of tickborne pathogens. Shotgun metagenomics is especially promising because it allows for detection of all tickborne bacteria, viruses, and parasites in a single specimen. Despite the potential advantages, there are several important challenges, including high cost, complexity of testing and interpretation, and slow turnaround time. No doubt, these challenges will diminish with increased use and advances in the field.

Diagnosis of infectious diseases in immunocompromised hosts using metagenomic next generation sequencing-based diagnostics

The diagnosis of infectious diseases in immunocompromised hosts presents unique challenges for the clinician. Metagenomic next generation sequencing (mNGS) based diagnostics that identify microbial nucleic acids in clinical samples (mNGS for pathogen identification or mNGSpi) may be a useful tool in addressing some of these challenges. Studies of mNGSpi in immunocompromised hosts have demonstrated that these diagnostics are capable of identifying causative organisms in a subset of patients for whom conventional testing has been negative. While these studies provide proof of concept for mNGSpi utility, they have a number of limitations, which make it difficult to confidently assess test performance and clinical impact based on current data. Future studies will likely feature larger cohort sizes and controlled interventional study designs that assess the impact of mNGSpi on clinical endpoints. They will also likely include assessments of the clinical value of data generated by mNGS beyond pathogen identification.

Clinical use of steroids in viral central nervous system (CNS) infections: three challenging cases

The role of adjunctive corticosteroids in reducing morbidity and mortality of viral CNS infections remains poorly defined. Clinicians are often left in a quagmire regarding steroid use in complex and rapidly evolving viral CNS infections. Limited studies have explored the underlying mechanisms behind the potential benefit of steroids. Here, we describe steroid use in three cases of viral CNS disease: varicella zoster virus (VZV), Powassan virus, and influenza A-associated acute necrotizing encephalopathy.

Fatal Human Infection with Evidence of Intrahost Variation of Eastern Equine Encephalitis Virus, Alabama, USA, 2019

Eastern equine encephalitis virus (EEEV) is an arbovirus in the family Togaviridae, genus Alphavirus, found in North America and associated with freshwater/hardwood swamps in the Atlantic, Gulf Coast, and Great Lakes regions. EEEV disease in humans is rare but causes substantial illness and death. To investigate the molecular epidemiology and microevolution of EEEV from a fatal case in Alabama, USA, in 2019, we used next-generation sequencing of serum and cerebrospinal fluid (CSF). Phylogenetic inference indicated that the infecting strain may be closely related to isolates from Florida detected during 2010-2014, suggesting potential seeding from Florida. EEEV detected in serum displayed a higher degree of variability with more single-nucleotide variants than that detected in the CSF. These data refine our knowledge of EEEV molecular epidemiologic dynamics in the Gulf Coast region and demonstrate potential quasispecies bottlenecking within the central nervous system of a human host.

Powassan Virus Infection Likely Acquired Through Blood Transfusion Presenting as Encephalitis in a Kidney Transplant Recipient

A kidney transplant patient without known tick exposure developed encephalitis 3 weeks after transplantation. During the transplant hospitalization, the patient had received a blood transfusion from an asymptomatic donor later discovered to have been infected with Powassan virus. Here, we describe a probable instance of transfusion-transmitted Powassan virus infection.

A Fatal Case of Powassan Virus Encephalitis

Powassan virus (POWV) is a flavivirus of the tick-borne encephalitis serogroup that causes a rare and potentially life-threatening neuroinvasive disease. Viral transmission occurs during zoonotic spillover from mammals by the bite of an infected tick in endemic regions of North America. The number of reported POWV cases has recently increased in the United States. We report a fatal case of POWV meningoencephalomyelitis in Northern Wisconsin following a documented tick bite. Histologic examination of the brain demonstrated widespread intraparenchymal and perivascular lymphohistocytic infiltration, microglial nodule formation, and marked neuronal degeneration, most severely involving the substantia nigra, anterior horn of spinal cord and cerebellum. Although no viral inclusions were seen in routine light microscopy, electron microscopy identified multiple neurons containing cytoplasmic clusters of virus particles ∼50 nm in diameter. POWV infection was confirmed using immunohistochemical analysis and reverse transcription-polymerase chain reaction. This report demonstrates in detail regional central nervous system involvement and ultrastructural characteristics of Powassan viral particles by transmission electron microscopy, while highlighting the utility of evaluating fixed autopsy tissues in cases of unexplained meningoencephalomyelitis.

Fatal Case of Chronic Jamestown Canyon Virus Encephalitis Diagnosed by Metagenomic Sequencing in Patient Receiving Rituximab

A 56-year-old man receiving rituximab who had months of neurologic symptoms was found to have Jamestown Canyon virus in cerebrospinal fluid by clinical metagenomic sequencing. The patient died, and postmortem examination revealed extensive neuropathologic abnormalities. Deep sequencing enabled detailed characterization of viral genomes from the cerebrospinal fluid, cerebellum, and cerebral cortex.

Jamestown Canyon virus in Massachusetts: clinical case series and vector screening

Jamestown Canyon virus (JCV) is a neuroinvasive arbovirus that is found throughout North America and increasingly recognized as a public health concern. From 2004 to 2012, an average of 1.7 confirmed cases were reported annually in the United States, whereas from 2013 to 2018 this figure increased over seventeen-fold to 29.2 cases per year. The rising number of reported human infections highlights the need for better understanding of the clinical manifestations and epidemiology of JCV. Here, we describe nine patients diagnosed with neuroinvasive JCV infection in Massachusetts from 2013, the year of the first reported case in the state, to 2017. Because current diagnostic testing relies on serology, which is complicated by cross-reactivity with related orthobunyaviruses and can be negative in immunosuppressed patients, we developed and evaluated an RT-qPCR assay for detection of JCV RNA. We tested this on the available archived serum from two patients, but did not detect viral RNA. JCV is transmitted by multiple mosquito species and its primary vector in Massachusetts is unknown, so we additionally applied the RT-qPCR assay and confirmatory RNA sequencing to assess JCV prevalence in a vector candidate, Ochlerotatus canadensis. We identified JCV in 0.6% of mosquito pools, a similar prevalence to neighboring Connecticut. We assembled the first Massachusetts JCV genome directly from a mosquito sample, finding high identity to JCV isolates collected over a 60-year period. Further studies are needed to reconcile the low vector prevalence and low rate of viral evolutionary change with the increasing number of reported cases.

Clinical features and laboratory diagnosis of emerging arthropod-transmitted viruses: A Report from the Pan American Society for Clinical Virology Clinical Practice Committee

Arthropod-borne viruses (arboviruses) are an increasing global threat due to their ability to cause human disease and their expanding geographical distribution. They circulate in nature between arthropod vectors and vertebrate hosts. Infection of susceptible human hosts leads to harmful developmental and neurological manifestations. Arboviruses have caused recent outbreaks with significant public health implications, such as the Zika virus outbreak in the western hemisphere which caused fetal abnormalities in some infected pregnant women, or Eastern Equine Encephalitis which caused 15 deaths in 2019. This review discusses several arboviral infections and their clinical manifestations while highlighting the importance of laboratory diagnostics to detect infections and current attempts at vaccine development. The ability to accurately diagnose an arbovirus infection is critical for initiating a timely response to infections in order to improve patient outcomes.

Powassan Virus Neuropathology and Genomic Diversity in Patients With Fatal Encephalitis

Background

Powassan virus (POWV) is an emerging cause of severe encephalitis; very little is known about human pathogenicity due to challenges in diagnosis and viral RNA recovery. We present 3 patients with fatal encephalitis due to POWV lineage II (deer tick virus).

Methods

We obtained 27 unique samples, including from brain biopsy and autopsy, and used metagenomic sequencing, quantitative reverse transcriptase polymerase chain reaction, and a newly developed CRISPR-based diagnostic assay to perform the first detailed characterization of POWV compartmentalization and genomics between and within human subjects.

Results

In all 3 patients, imaging and histopathology findings were notable for profound cerebellar involvement. All patients were initially diagnosed with POWV by metagenomic sequencing, and 2 of the 3 had negative clinical testing by serology. We detected POWV RNA in 13 clinical samples; levels were highest in the cerebellum, and there was very little involvement of peripheral tissue. We assembled complete POWV genomes from 8 samples, providing unique information about the strains of POWV lineage II (deer tick virus) that infect humans.

Conclusions

We demonstrate the utility of molecular assays for detecting POWV infection, including in seronegative patients, and nominate viral genomic features that may relate to human infection and neuropathogenicity. The cerebellum was identified as a key target POWV in fatal infection, by radiological and histopathological findings as well as molecular testing.

Powassan Virus Encephalitis Following Brief Attachment of Connecticut Deer Ticks

BACKGROUND

Powassan virus (POWV) is a tick-transmitted pathogen that may cause severe encephalitis; experimentally, it can be transmitted within just 15 minutes following a tick bite. The deer tick virus subtype of POWV (DTV) is transmitted by the deer tick and is the likely cause of the increase in the number of POWV cases reported in the United States. However, DTV has only been definitively documented in 6 patients by molecular analysis of the virus.

METHODS

Two patients from Connecticut with encephalitis, who had a recent deer tick bite, were evaluated by the relevant serologic tests to determine if they had been infected with POWV. Evaluation also included molecular testing of an adult deer tick that had been removed from one of the patients.

RESULTS

We documented neuroinvasive POWV infection in 2 children from Connecticut. Based on the results of testing the tick removed from case 2, this patient was infected by DTV, representing the 7th reported case and the first documented case of DTV infection in a child. Of note, the duration of the tick bites in both cases was very short.

CONCLUSIONS

We provide the first clinical and epidemiologic evidence that POWV/DTV can be rapidly transmitted to a human host, that is, within hours of tick attachment, which is distinctive when compared to other deer tick-transmitted infections such as Lyme disease.

Metagenomics for neurological infections - expanding our imagination

Over the past two decades, the diagnosis rate for patients with encephalitis has remained poor despite advances in pathogen-specific testing such as PCR and antigen assays. Metagenomic next-generation sequencing (mNGS) of RNA and DNA extracted from cerebrospinal fluid and brain tissue now offers another strategy for diagnosing neurological infections. Given that mNGS simultaneously assays for a wide range of infectious agents in an unbiased manner, it can identify pathogens that were not part of a neurologist’s initial differential diagnosis either because of the rarity of the infection, because the microorganism has not been previously associated with a clinical phenotype or because it is a newly discovered organism. This Review discusses the technical advantages and pitfalls of cerebrospinal fluid mNGS in the context of patients with neuroinflammatory syndromes, including encephalitis, meningitis and myelitis. We also speculate on how mNGS testing potentially fits into current diagnostic testing algorithms given data on mNGS test performance, cost and turnaround time. Finally, the Review highlights future directions for mNGS technology and other hypothesis-free testing methodologies that are in development.

This Review discusses the advantages and pitfalls of metagenomic next-generation sequencing (mNGS) in patients with encephalitis, meningitis and myelitis. The authors outline data on mNGS test performance, cost and turnaround time and highlight future directions for mNGS technology.

Meningoencephalitis remains a challenging diagnosis owing to the multitude of possible infectious and autoimmune causes.

Meningoencephalitis is associated with a high rate of morbidity and mortality and requires prompt diagnosis and treatment.

Metagenomic next-generation sequencing (mNGS) is now a clinically validated test for neuroinfectious diseases that can aid clinicians with a timely diagnosis.

mNGS can improve the detection of pathogens that were missed by clinicians or on standard direct testing.

mNGS does not perform well when indirect tests are required to make the diagnosis (for example, serology), when infections are compartmentalized and for certain low abundance pathogens.

The clinical context of the case is required when interpreting the results of mNGS.

Development of a small animal model for deer tick virus pathogenesis mimicking human clinical outcome

Powassan virus (POWV) is a tick-borne flavivirus that encompasses two genetic lineages, POWV (Lineage I) and deer tick virus (DTV, Lineage II). In recent years, the incidence of reported POWV disease cases has increased, coupled with an expanded geographic range of the DTV tick vector, Ixodes scapularis. POWV and DTV are serologically indistinguishable, and it is not known whether clinical manifestations, pathology, or disease outcome differ between the two viruses. Six-week-old male and female BALB/c mice were footpad-inoculated with DTV doses ranging from 10¹ to 10⁵ FFU. Dose-independent mortality, morbidity, and organ viral loads were observed for mice inoculated with sequentially increasing doses of DTV. By study completion, all surviving mice had cleared their viremias but detectable levels of negative-sense DTV RNA were present in the brain, indicating viral persistence of infectious DTV in the central nervous system. For mice that succumbed to disease, neuropathology revealed meningoencephalitis characterized by microscopic lesions with widespread distribution of viral RNA in the brain. These findings, coupled with the rapid onset of neurological signs of disease and high viral titers in nervous tissue, highlight the neurotropism of DTV in this mouse model. Additionally, disease outcome for DTV-infected mice was not affected by sex, as males and females were equally susceptible to disease. This is the first study to comprehensively characterize the clinical disease outcome in a small animal model across a spectrum of POWV/DTV infection doses. Here, we developed a small animal model for DTV pathogenesis that mimics the manifestations of POWV disease in humans. Since it is currently not known whether DTV and POWV differ in their capacity to cause human disease, the animal model detailed in our study could be utilized in future comparative pathogenesis studies, or as a platform for testing the efficacy of vaccines, and anti-virals.

Powassan virus (POWV) is a tick-borne flavivirus that can result in a fatal encephalitic disease in humans. Although POWV is closely related to deer tick virus (DTV), each virus is maintained in nature by unique transmission cycles. Because POWV and DTV are serologically indistinguishable and must be differentiated by genetic sequence analysis, an unknown portion of previously reported POWV cases may have actually been DTV cases. Overall, the scientific literature is sparse when it comes to describing confirmed DTV cases or the neurovirulence and clinical outcome for DTV-infected mice. Our study is the first to comprehensively characterize the survival rates, timeline of clinical disease, and tissue distribution of virus for mice infected with a range of DTV doses. Signs of disease in the DTV-infected mice mimicked the course of human clinical disease where neurological manifestations were preceded by a generalized febrile illness. Sequentially increasing doses of DTV did not elicit increased mortality rates or organ viral loads, which suggests that in this mouse model, virus infection and replication in tissues is independent of the infection dose. Our findings support the use of this mouse model in future DTV pathogenesis studies.

Mild COVID-19 infection despite chronic B cell depletion in a patient with aquaporin-4-positive neuromyelitis optica spectrum disorder

Coronavirus disease 2019 (COVID-19) is caused by the novel coronavirus SARS-CoV-2, which affects the lung and other organs. After an incubation period of 3-14 days, the infection presents with symptoms of variable severity, from mild flu-like disease to severe pneumonia and cytokine storm with increased mortality. Immunosuppressed patients may have higher risk of adverse outcomes; hence, there is an urgent need to evaluate the immune response and clinical outcomes of SARS-CoV-2 infection in these patients. Here, we report a 59-year-old woman with aquaporin-4-positive (AQPR4+) neuromyelitis Optica treated with rituximab who developed mild respiratory symptoms with COVID-19, despite B cell depletion at the time of infection.

Lyme Neuroborreliosis: Clinical Outcomes, Controversy, Pathogenesis, and Polymicrobial Infections

Lyme borreliosis is the object of numerous misconceptions. In this review, we revisit the fundamental manifestations of neuroborreliosis (meningitis, cranial neuritis, and radiculoneuritis), as these have withstood the test of time. We also discuss other manifestations that are less frequent. Stroke, as a manifestation of Lyme neuroborreliosis, is considered in the context of other infections. The summary of the literature regarding clinical outcomes of neuroborreliosis leads to its controversies. We also include new information on pathogenesis and on the polymicrobial nature of tick-borne diseases. In this way, we update the review that we wrote in this journal in 1995. ANN NEUROL 2019;85:21-31.

Polymicrobial Nature of Tick-Borne Diseases

Tick-borne diseases have doubled in the last 12 years, and their geographic distribution has spread as well. The clinical spectrum of tick-borne diseases can range from asymptomatic to fatal infections, with a disproportionate incidence in children and the elderly. In the last few years, new agents have been discovered, and genetic changes have helped in the spread of pathogens and ticks. Polymicrobial infections, mostly in Ixodes scapularis, can complicate diagnostics and augment disease severity. Amblyomma americanum ticks have expanded their range, resulting in a dynamic and complex situation, possibly fueled by climate change. To document these changes, using molecular biology strategies for pathogen detection, an assessment of 12 microbes (9 pathogens and 3 symbionts) in three species of ticks was done in Suffolk County, New York. At least one agent was detected in 63% of I. scapularis ticksBorrelia burgdorferi was the most prevalent pathogen (57% in adults; 27% in nymphs), followed by Babesia microti (14% in adults; 15% in nymphs), Anaplasma phagocytophilum (14% in adults; 2% in nymphs), Borrelia miyamotoi (3% in adults), and Powassan virus (2% in adults). Polymicrobial infections were detected in 22% of I. scapularis ticks, with coinfections of B. burgdorferi and B. microti (9%) and of B. burgdorferi and A. phagocytophilum (7%). Three Ehrlichia species were detected in 4% of A. americanum ticks. The rickettsiae constituted the largest prokaryotic biomass of all the ticks tested and included Rickettsia amblyommatis, Rickettsia buchneri, and Rickettsia montanensis The high rates of polymicrobial infection in ticks present an opportunity to study the biological interrelationships of pathogens and their vectors.IMPORTANCE Tick-borne diseases have increased in prevalence in the United States and abroad. The reasons for these increases are multifactorial, but climate change is likely to be a major factor. One of the main features of the increase is the geographic expansion of tick vectors, notably Amblyomma americanum, which has brought new pathogens to new areas. The clinical spectrum of tick-borne diseases can range from asymptomatic to fatal infections, with a disproportionate incidence in children and the elderly. In addition, new pathogens that are cotransmitted by Ixodes scapularis have been discovered and have led to difficult diagnoses and to disease severity. Of these, Borrelia burgdorferi, the agent of Lyme disease, continues to be the most frequently transmitted pathogen. However, Babesia microti, Borrelia miyamotoi (another spirochete), Anaplasma phagocytophilum, and Powassan virus are frequent cotransmitted agents. Polymicrobial infection has important consequences for the diagnosis and management of tick-borne diseases.

Diagnostic Testing in Central Nervous System Infection

Patients with central nervous system (CNS) infection experience very high levels of morbidity and mortality, in part because of the many challenges inherent to the diagnosis of CNS infection and identification of a causative pathogen. The clinical presentation of CNS infection is nonspecific, so clinicians must often order and interpret many diagnostic tests in parallel. This can be a daunting task given the large number of potential pathogens and the availability of different testing modalities. Here, we review traditional diagnostic techniques including Gram stain and culture, serology, and polymerase chain reaction (PCR). We highlight which of these are recommended for the pathogens most commonly tested among U.S. patients with suspected CNS infection. Finally, we describe the newer broad-range diagnostic approaches, multiplex PCR and metagenomic sequencing, which are increasingly used in clinical practice.

Anaplasma phagocytophilum presenting with orchitis in a renal transplant recipient

Human granulocytic anaplasmosis (HGA), caused by Anaplasma phagocytophilum, is an emerging tick-borne disease. It is spread by the black-legged deer tick Ixodes scapularis that serves as the vector for six human pathogens. HGA is still rarely reported in solid organ transplant recipients. In solid organ transplant recipients, orchitis has been reported secondary to chickenpox, tuberculosis and infections due to Listeria monocytogenes and Nocardia asteroides. Orchitis as a presenting feature of HGA infection has only been reported in animals. We present a unique case of a renal transplant recipient with HGA that presented as orchitis. We also compare the clinical presentation and laboratory findings of our patient with other cases of HGA in transplant recipients. To the best of our knowledge, our patient is one of the first cases of A phagocytophilum mono-infection causing a classical presentation of orchitis in a transplant patient.

Severe Epididymo-Orchitis and Encephalitis Complicating Anti-PD-1 Therapy

BACKGROUND

Immune checkpoint inhibitors such as pembrolizumab and nivolumab have emerged as active treatment options for patients with many cancers, including metastatic melanoma, but can also cause symptomatic or life-threatening immune-related adverse events, including encephalitis. Epididymitis and orchitis are rare complications of these therapies.

CASE PRESENTATION

We describe herein a patient with metastatic melanoma who developed epididymo-orchitis followed by encephalitis while receiving pembrolizumab. The patient developed testicular pain and fever after his third dose of pembrolizumab; ultrasound evaluation demonstrated bilateral epididymo-orchitis. He then developed headaches, fever, and altered mental status over the next week and was admitted to the hospital. Lumbar puncture revealed inflammatory changes consistent with meningoencephalitis; he did not improve with broad-spectrum antibiotics, and an extensive workup for infectious etiologies, including cerebrospinal fluid testing using a clinical metagenomic next-generation sequencing assay, was negative. He received high-dose steroids for suspected autoimmune encephalitis, and both his orchitis and meningoencephalitis improved rapidly after one dose. He fully recovered after a 5-week taper of oral steroids.

DISCUSSION

Here, we report a case of epididymo-orchitis complicating immune checkpoint inhibitor therapy. This patient subsequently developed severe encephalitis but rapidly improved with steroids. Clinicians should be aware of rare complications of these agents.

KEY POINTS

Epididymo-orchitis is a rare and potentially life-threatening complication of anti-programmed death protein 1 (anti-PD-1) therapy.For patients on anti-PD-1 therapy who develop either epididymo-orchitis or epididymitis without clear infectious cause, immune-related adverse events should be considered in the differential diagnosis.If severe, epididymo-orchitis related to anti-PD-1 therapy may be treated with high-dose corticosteroids.