Neurological suppression of diaphragm electromyographs in hamsters infected with West Nile virus

Rehabilitation approaches in West Nile Virus survivors: a systematic review

INTRODUCTION

Periodic increases in West Nile virus (WNV) infections have been documented. Proper rehabilitative management is essential for these patients, who may experience limitations in daily activities even after the resolution of the acute infection. Since there are currently no globally accepted guidelines, our aim is to conduct a best-evidence synthesis on rehabilitative management for patients with neuroinvasive WNV.

EVIDENCE ACQUISITION

We screened the literature with two independent researchers conducting searches on PubMed, Embase, SCOPUS, and Google Scholar databases for WNV-related studies in the field of rehabilitation. Suitable studies were identified and selected through a rigorous process. The review includes original research articles published up to August 15, 2023.

EVIDENCE SYNTHESIS

Despite the potential for bias in the studies, the literature suggests that a comprehensive and interdisciplinary rehabilitation program, which includes physical therapy with neuromotor and respiratory interventions, occupational therapy, neurocognitive interventions, and speech therapy for dysphagia and communication issues, can lead to functional improvement in WNV patients. This program should be tailored to address each patient's specific challenges, and the duration of the rehabilitation program may vary depending on the individual patient's needs.

CONCLUSIONS

Even if additional research with larger cohorts and higher evidence levels is needed for a comprehensive understanding of WNV patient rehabilitation, an early and comprehensive rehabilitation approach addressing respiratory, neuromuscular, and cognitive aspects appears effective for WNV patient recovery.

Current Understanding of West Nile Virus Clinical Manifestations, Immune Responses, Neuroinvasion, and Immunotherapeutic Implications

West Nile virus (WNV) is the most common mosquito-borne virus in North America. WNV-associated neuroinvasive disease affects all ages, although elderly and immunocompromised individuals are particularly at risk. WNV neuroinvasive disease has killed over 2300 Americans since WNV entered into the United States in the New York City outbreak of 1999. Despite 20 years of intensive laboratory and clinical research, there are still no approved vaccines or antivirals available for human use. However, rapid progress has been made in both understanding the pathogenesis of WNV and treatment in clinical practices. This review summarizes our current understanding of WNV infection in terms of human clinical manifestations, host immune responses, neuroinvasion, and therapeutic interventions.

Syrian Hamster as an Animal Model for the Study on Infectious Diseases

Infectious diseases still remain one of the biggest challenges for human health. In order to gain a better understanding of the pathogenesis of infectious diseases and develop effective diagnostic tools, therapeutic agents, and preventive vaccines, a suitable animal model which can represent the characteristics of infectious is required. The Syrian hamster immune responses to infectious pathogens are similar to humans and as such, this model is advantageous for studying pathogenesis of infection including post-bacterial, viral and parasitic pathogens, along with assessing the efficacy and interactions of medications and vaccines for those pathogens. This review summarizes the current status of Syrian hamster models and their use for understanding the underlying mechanisms of pathogen infection, in addition to their use as a drug discovery platform and provides a strong rationale for the selection of Syrian hamster as animal models in biomedical research. The challenges of using Syrian hamster as an alternative animal model for the research of infectious diseases are also addressed.

Efficacy of the broad-spectrum antiviral compound BCX4430 against Zika virus in cell culture and in a mouse model

Zika virus (ZIKV) is currently undergoing pandemic emergence. While disease is typically subclinical, severe neurologic manifestations in fetuses and newborns after congenital infection underscore an urgent need for antiviral interventions. The adenosine analog BCX4430 has broad-spectrum activity against a wide range of RNA viruses, including potent in vivo activity against yellow fever, Marburg and Ebola viruses. We tested this compound against African and Asian lineage ZIKV in cytopathic effect inhibition and virus yield reduction assays in various cell lines. To further evaluate the efficacy in a relevant animal model, we developed a mouse model of severe ZIKV infection, which recapitulates various human disease manifestations including peripheral virus replication, conjunctivitis, encephalitis and myelitis. Time-course quantification of viral RNA accumulation demonstrated robust viral replication in several relevant tissues, including high and persistent viral loads observed in the brain and testis. The presence of viral RNA in various tissues was confirmed by an infectious culture assay as well as immunohistochemical staining of tissue sections. Treatment of ZIKV-infected mice with BCX4430 significantly improved outcome even when treatment was initiated during the peak of viremia. The demonstration of potent activity of BCX4430 against ZIKV in a lethal mouse model warrant its continued clinical development.

Phrenic nerve deficits and neurological immunopathology associated with acute West Nile virus infection in mice and hamsters

Neurological respiratory deficits are serious outcomes of West Nile virus (WNV) disease. WNV patients requiring intubation have a poor prognosis. We previously reported that WNV-infected rodents also appear to have respiratory deficits when assessed by whole-body plethysmography and diaphragmatic electromyography. The purpose of this study was to determine if the nature of the respiratory deficits in WNV-infected rodents is neurological and if deficits are due to a disorder of brainstem respiratory centers, cervical spinal cord (CSC) phrenic motor neuron (PMN) circuitry, or both. We recorded phrenic nerve (PN) activity and found that in WNV-infected mice, PN amplitude is reduced, corroborating a neurological basis for respiratory deficits. These results were associated with a reduction in CSC motor neuron number. We found no dramatic deficits, however, in brainstem-mediated breathing rhythm generation or responses to hypercapnia. PN frequency and pattern parameters were normal, and all PN parameters changed appropriately upon a CO₂ challenge. Histological analysis revealed generalized microglia activation, astrocyte reactivity, T cell and neutrophil infiltration, and mild histopathologic lesions in both the brainstem and CSC, but none of these were tightly correlated with PN function. Similar results in PN activity, brainstem function, motor neuron number, and histopathology were seen in WNV-infected hamsters, except that histopathologic lesions were more severe. Taken together, the results suggest that respiratory deficits in acute WNV infection are primarily due to a lower motor neuron disorder affecting PMNs and the PN rather than a brainstem disorder. Future efforts should focus on markers of neuronal dysfunction, axonal degeneration, and myelination.

Inhibition of West Nile virus by calbindin-D28k

Evidence indicates that West Nile virus (WNV) employs Ca²⁺ influx for its replication. Moreover, calcium buffer proteins, such as calbindin D28k (CB-D28k), may play an important role mitigating cellular destruction due to disease processes, and more specifically, in some neurological diseases. We addressed the hypothesis that CB-D28k inhibits WNV replication in cell culture and infected rodents. WNV envelope immunoreactivity (ir) was not readily co-localized with CB-D28k ir in WNV-infected Vero 76 or motor neuron-like NSC34 cells that were either stably or transiently transfected with plasmids coding for CB-D28k gene. This was confirmed in cultured cells fixed on glass coverslips and by flow cytometry. Moreover, WNV infectious titers were reduced in CB-D28k-transfected cells. As in cell culture studies, WNV env ir was not co-localized with CB-D28k ir in the cortex of an infected WNV hamster, or in the hippocampus of an infected mouse. Motor neurons in the spinal cord typically do not express CB-D28k and are susceptible to WNV infection. Yet, CB-D28k was detected in the surviving motor neurons after the initial phase of WNV infection in hamsters. These data suggested that induction of CB-D28k elicit a neuroprotective response to WNV infection.

Comparative pathology of neurovirulent lineage 1 (NY99/385) and lineage 2 (SPU93/01) West Nile virus infections in BALBc mice

The pathology in mice infected with neurovirulent South African lineage 2 West Nile virus (WNV) strains has not previously been described. Three- to 4-month-old male BALBc mice were infected with South African neurovirulent lineage 2 (SPU93/01) or lineage 1 (NY385/99) WNV strains and the gross and microscopic central nervous system (CNS) and extra-CNS pathology of both investigated and compared. Mice infected with both lineages showed similar illness, paralysis, and death from days 7 to 11 postinfection (PI). Two survivors of each lineage were euthanized on day 21 PI. WNV infection was confirmed by nested real-time reverse transcription polymerase chain reaction of tissues, mostly brain, in the majority of mice euthanized sick or that died and in 1 healthy lineage 2 survivor. Gross lesions caused by both lineages were identical and included marked gastric and proximal small intestinal fluid distension as described in a previous mouse study, but intestinal microscopic lesions differed. CNS lesions were subtle. Immunohistochemical (IHC)-positive labeling for WNV E protein was found in neurons multifocally in the brain of 3 lineage 1-infected and 3 lineage 2-infected mice from days 9 to 11 PI, 4 of these including brainstem neurons, and of cecal myenteric ganglion neurons in 1 lineage 2-infected day 8 PI mouse. Findings supported hypotheses in hamsters that gastrointestinal lesions are likely of brainstem origin. Ultrastructurally, virus-associated cytoplasmic vesicular or crystalline structures, or amorphous structures, were found to label IHC positive in control-positive avian cardiomyocytes and mouse thalamic neurons, respectively, and WNV-like 50-nm particles, which were scarce, did not label.

Autonomic deficit not the cause of death in West Nile virus neurological disease

Introduction

Some West Nile virus (WNV)-infected patients have been reported to manifest disease signs consistent with autonomic dysfunction. Moreover, WNV infection in hamsters causes reduced electromyography amplitudes of the gastrointestinal tract and diaphragm, and they have reduced heart rate variability (HRV), a read-out for the parasympathetic autonomic function.

Methods

HRV was measured in both hamsters and mice using radiotelemetry to identify autonomic deficits. To identify areas of WNV infection within the medulla oblongata mapping to the dorsal motor nucleus of vagus (DMNV) and the nucleus ambiguus (NA), fluorogold dye was injected into the cervical trunk of the vagus nerve of hamsters. As a measurement of the loss of parasympathetic function, tachycardia was monitored contiguously over the time course of the disease.

Results

Decrease of HRV did not occur in all animals that died, which is not consistent with autonomic function being the mechanism of death. Fluorogold-stained cells in the DMNV were not stained for WNV envelope protein. Fourteen percent of WNV-stained cells were co-localized with fluorogold-stained cells in the NA. These data, however, did not suggest a fatal loss of autonomic functions because tachycardia was not observed in WNV-infected hamsters.

Conclusion

Parasympathetic autonomic function deficit was not a likely mechanism of death in WNV-infected rodents and possibly in human patients with fatal WN neurological disease.

Neurological approaches for investigating West Nile virus disease and its treatment in rodents

West Nile virus (WNV) has had a major public health impact since its emergence in the Western Hemisphere; in 2012, nearly 3000 cases of WN neuroinvasive disease were identified in the United States. The underlying mechanisms of WN neurologic disease can only be studied to a limited extent in patients, but can be investigated in much greater detail in animal models. In this paper, we describe how we and others have employed a variety of electrophysiological and neurological techniques to study experimental WNV infections in hamsters and mice. The methods have included electrophysiological motor unit number estimation; optogenetic photoactivation of the spinal cord and electromyography; plethysmography; measurement of heart rate variability as an indication of autonomic nervous system dysfunction; and an assessment of spatial memory loss using the Morris water maze. These techniques provide a more refined assessment of disease manifestations in rodents than traditional measurements of weight loss and mortality, and should make it possible to identify targets for therapeutic intervention and to directly assess the effects of novel treatments.

Fatal neurological respiratory insufficiency is common among viral encephalitides

Background. Neurological respiratory insufficiency strongly correlates with mortality among rodents infected with West Nile virus (WNV), which suggests that this is a primary mechanism of death in rodents and possibly fatal West Nile neurological disease in human patients.

Methods. To explore the possibility that neurological respiratory insufficiency is a broad mechanism of death in cases of viral encephalitis, plethysmography was evaluated in mice infected with 3 flaviviruses and 2 alphaviruses. Pathology was investigated by challenging the diaphragm, using electromyography with hypercapnia and optogenetic photoactivation.

Results. Among infections due to all but 1 alphavirus, death was strongly associated with a suppressed minute volume. Virally infected mice with a very low minute volume did not neurologically respond to hypercapnia or optogenetic photoactivation of the C4 cervical cord. Neurons with the orexin 1 receptor protein in the ventral C3–5 cervical cord were statistically diminished in WNV-infected mice with a low minute volume as compared to WNV-infected or sham-infected mice without respiratory insufficiency. Also, WNV-infected cells were adjacent to neurons with respiratory functions in the medulla.

Conclusions. Detection of a common neurological mechanism of death among viral encephalitides creates opportunities to create broad-spectrum therapies that target relevant neurological cells in patients with types of viral encephalitis that have not been treatable in the past.

Respiratory insufficiency correlated strongly with mortality of rodents infected with West Nile virus

West Nile virus (WNV) disease can be fatal for high-risk patients. Since WNV or its antigens have been identified in multiple anatomical locations of the central nervous system of persons or rodent models, one cannot know where to investigate the actual mechanism of mortality without careful studies in animal models. In this study, depressed respiratory functions measured by plethysmography correlated strongly with mortality. This respiratory distress, as well as reduced oxygen saturation, occurred beginning as early as 4 days before mortality. Affected medullary respiratory control cells may have contributed to the animals' respiratory insufficiency, because WNV antigen staining was present in neurons located in the ventrolateral medulla. Starvation or dehydration would be irrelevant in people, but could cause death in rodents due to lethargy or loss of appetite. Animal experiments were performed to exclude this possibility. Plasma ketones were increased in moribund infected hamsters, but late-stage starvation markers were not apparent. Moreover, daily subcutaneous administration of 5% dextrose in physiological saline solution did not improve survival or other disease signs. Therefore, infected hamsters did not die from starvation or dehydration. No cerebral edema was apparent in WNV- or sham-infected hamsters as determined by comparing wet-to-total weight ratios of brains, or by evaluating blood-brain-barrier permeability using Evans blue dye penetration into brains. Limited vasculitis was present in the right atrium of the heart of infected hamsters, but abnormal electrocardiograms for several days leading up to mortality did not occur. Since respiratory insufficiency was strongly correlated with mortality more than any other pathological parameter, it is the likely cause of death in rodents. These animal data and a poor prognosis for persons with respiratory insufficiency support the hypothesis that neurological lesions affecting respiratory function may be the primary cause of human WNV-induced death.

The contribution of rodent models to the pathological assessment of flaviviral infections of the central nervous system

Members of the genus Flavivirus are responsible for a spectrum of important neurological syndromes in humans and animals. Rodent models have been used extensively to model flavivirus neurological disease, to discover host-pathogen interactions that influence disease outcome, and as surrogates to determine the efficacy and safety of vaccines and therapeutics. In this review, we discuss the current understanding of flavivirus neuroinvasive disease and outline the host, viral and experimental factors that influence the outcome and reliability of virus infection of small-animal models.

Autonomic nervous dysfunction in hamsters infected with West Nile virus

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

Treatment of spatial memory impairment in hamsters infected with West Nile virus using a humanized monoclonal antibody MGAWN1

In addition to functional disorders of paresis, paralysis, and cardiopulmonary complications, subsets of West Nile virus (WNV) patients may also experience neurocognitive deficits and memory disturbances. A previous hamster study has also demonstrated spatial memory impairment using the Morris water maze (MWM) paradigm. The discovery of an efficacious therapeutic antibody MGAWN1 from pre-clinical rodent studies raises the possibility of preventing or treating WNV-induced memory deficits. In the current study, hamsters were treated intraperitoneally (i.p.) with 32 mg/kg of MGAWN1 at 4.5 days after subcutaneously (s.c.) challenging with WNV. As expected, MGAWN1 prevented mortality, weight loss, and improved food consumption of WNV-infected hamsters. The criteria for entry of surviving hamsters into the study were that they needed to have normal motor function (forelimb grip strength, beam walking) and normal spatial reference memory in the MWM probe task. Twenty-eight days after the acute phase of the disease had passed, MGAWN1- and saline-treated infected hamsters were again trained in the MWM. Spatial memory was evaluated 48 h after this training in which the hamsters searched for the location where a submerged escape platform had been positioned. Only 56% of infected hamsters treated with saline spent more time in the correct quadrant than the other three quadrants, as compared to 92% of MGAWN1-treated hamsters (P⩽0.05). Overall these studies support the possibility that WNV can cause spatial memory impairment and that therapeutic intervention may be considered.