Of Mice and Men: Protective and Pathogenic Immune Responses to West Nile virus Infection

West Nile Virus (WNV): One-Health and Eco-Health Global Risks

West Nile virus (WNV) is an important zoonotic pathogen belonging to the Flaviviridae family, which is endemic in some areas and emerging in others. WNV is transmitted by blood-sucking mosquitoes of the genus Culicoides, Aedes, and Anopheles, and the infection can cause different clinical symptoms. The most common and benign illness in humans is West Nile fever (WNF), but a lethal neurological disease (WNND), related to the neuro-invasiveness of WNV lineage 2, represents the highest health risk of WNV infection. The neuro-clinical form is recognized in mammals (land and cetaceans), particularly in humans (elderly or immunosuppressed) and in horses, avian species, and wildlife animals ranging free or in a zoological setting. This review highlights the most relevant data regarding epidemiology, virology, pathogenesis and immunity, clinical signs and differential diagnosis, pathology and imaging, histopathology and gross pathology, economic impact, influence of climate change, and surveillance of WNV. Climate change has favored the wide spread of WNV in many areas of the globe and consequent One-Health and Eco-Health emergencies, influencing the health of human beings, animals, and ecosystems.

Clinical, Prognostic, and Longitudinal Functional and Neuropsychological Features of West Nile Virus Neuroinvasive Disease in the United States: A Systematic Review and Meta-Analysis

OBJECTIVE

West Nile virus (WNV) is the most common cause of arboviral disease in the United States. Approximately 1% of infections involve the nervous system, most commonly resulting in West Nile encephalitis (WNE), West Nile meningitis (WNM), or acute flaccid paralysis (AFP).

METHODS

In this systematic review, we characterized comprehensively the diagnostic and clinical features of WNV neuroinvasive disease (WNND) in the United States, as well as the evidence regarding prognostic factors and long-term outcomes of WNND.

RESULTS

We identified 47 relevant studies reporting data on acute or longitudinal features of WNND. Across studies, the most common presenting symptoms were fever (88%), nausea/vomiting (58%), and fatigue (50%) coupled neurologically with headache (50%), altered mental status (39%), and focal weakness (32%). Pooled mortality was 9.2%, and 42.1% of reported cases required intensive care unit (ICU) admission. In meta-analyses, chronic kidney disease (odds ratio [OR] = 5.99, 95% confidence interval [CI] = 2.71-13.23), diabetes mellitus (OR = 2.43, 95% CI = 1.54-3.84), and hypertension (OR = 4.01, 95% CI = 2.39-6.72) were associated with an increased risk of mortality. Multidomain neurocognitive impairment was reported in several studies at post-hospitalization follow-up, although with marked heterogeneity between study methodology. Subjective neurocognitive impairment, most notably fatigue (37-75%), memory concerns (11-57%), concentration deficits (17-48%), and depression (17-38%), were also common at post-hospitalization follow-up.

INTERPRETATION

These findings underscore the significant mortality and morbidity of WNND in the acute and long-term setting. Our findings may additionally provide utility for risk stratification of hospitalized patients with WNND and suggest the need for further evaluation of novel therapeutics to prevent substantial disease-associated acute and long-term disability. ANN NEUROL 2025.

Unique Cytokine Response in West Nile Virus Patients Who Developed Chronic Kidney Disease: A Prospective Cohort Study

West Nile virus (WNV) is a widespread and devastating disease, especially in those who develop neuroinvasive disease. A growing body of evidence describes sequelae years after infection, including neurological complications and chronic kidney disease (CKD). Eighty-nine out of 373 WNV-positive cases were followed for approximately two years and compared to 127 WNV-negative controls with and without CKD. Adjusted risk ratios (aRRs) were calculated via a log binomial regression to determine the impact of WNV exposure and other possible confounders on the likelihood of developing CKD. Cytokine profiles of WNV patients and controls were evaluated to characterize differences and describe potential underlying pathophysiological mechanisms. The associated risk for developing CKD was significantly associated with history of WNV infection (aRR = 1.91, 95% CI 1.13–3.25). Additionally, five distinct cytokines were found to be significantly associated with WNV infection (eotaxin, IL-8, IL-12p70, IP-10, and TNFα) after the p-value was adjusted to <0.0019 due to the Bonferroni correction. These data support that WNV infection is an independent risk factor for CKD, even after accounting for confounding comorbidities. WNV participants who developed CKD had high activity of proinflammatory markers, indicating underlying inflammatory disease. This study provides new insights into CKD resultant of WNV infection.

Neuroinvasion and Inflammation in Viral Central Nervous System Infections

Neurotropic viruses can cause devastating central nervous system (CNS) infections, especially in young children and the elderly. The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) have been described as relevant sites of entry for specific viruses as well as for leukocytes, which are recruited during the proinflammatory response in the course of CNS infection. In this review, we illustrate examples of established brain barrier models, in which the specific reaction patterns of different viral families can be analyzed. Furthermore, we highlight the pathogen specific array of cytokines and chemokines involved in immunological responses in viral CNS infections. We discuss in detail the link between specific cytokines and chemokines and leukocyte migration profiles. The thorough understanding of the complex and interrelated inflammatory mechanisms as well as identifying universal mediators promoting CNS inflammation is essential for the development of new diagnostic and treatment strategies.

Tissue-specific transcription profile of cytokine and chemokine genes associated with flavivirus control and non-lethal neuropathogenesis in rabbits

We previously showed that New Zealand White (NZWRs) and cottontail rabbits (CTRs) are a suitable model for studying immune mechanisms behind virus control and non-lethal neuropathogenesis associated with West Nile virus (WNV) and Murray Valley encephalitis virus (MVEV) infections. In the current study, we observed that MVEV infection induced high IFNα, TNFα, IL6, and CXCL10 transcript levels in the brains of weanling NZWRs, unlike infection with the less virulent WNVNSW2011. These transcript levels also correlated with encephalitis severity. Widespread STAT1 protein expression in brain with moderate neuropathology suggests that IFN-I signaling is crucial for limiting neural infection and mediating non-lethal neuropathogenesis. Unlike NZWRs, CTRs limit neuroinvasion without upregulation of many cytokine/chemokine transcripts, suggesting a species-dependent virus control mechanism. However, the common IFNγ, TNFα and IL6 transcript upregulation in specific lymphoid organs suggest some conserved elements in the response against flaviviruses, unique to all rabbits.