WEST NILE VIRUS DISEASE CAN BE NEUROINVASIVE

C. D’Aurizio¹ and F. Danzo^2*

¹ Department of Neurorehabilitation, Popoli Hospital, Popoli, Italy;
² Division of Respiratory Diseases, “L. Sacco” University Hospital, Università degli Studi di Milano, 20122 Milano, Italy.

*Correspondence to:
Fiammetta Danzo,
Division of Respiratory Diseases,
“L. Sacco” University Hospital,
Università degli Studi di Milano,
20122 Milan, Italy.
e-mail: fiammetta.danzo@gmail.com

Received: 07 February, 2025 Accepted: 13 March, 2025

ISSN 2279-5855 print ISSN 2974-6345 online. Copyright © by BIOLIFE 2025 This publication and/or article is for individual use only and may not be further reproduced without written permission from the copyright holder. Unauthorized reproduction may result in financial and other penalties. Disclosure: All authors report no conflicts of interest relevant to this article.

ABSTRACT

West Nile virus (WNV) is a single-stranded, positive-sequence RNA virus (ssRNA+) transmitted by mosquitoes of the Culex genus. WNV enters the host cell by endocytosis and replicates via the E protein, interacting with specific cellular receptors. Eighty percent of infected people show no symptoms, but 20% may experience a mild form with fever, headache, fatigue, and mild nausea, or a neuroinvasive form that can affect the elderly or immunocompromised, which can cause fever and encephalitis, manifesting with inflammation. WNV infects the central nervous system (CNS) by increasing the permeability of the blood-brain barrier (BBB). Brain infection affects microglia, which are activated to produce proinflammatory cytokines, causing neuropathy with activation of endothelial cells, neurons, and astrocytes.

KEYWORDS: West Nile virus, mosquito, central nervous system, brain, neuroinvasive disease

INTRODUCTION

West Nile virus (WNV) is transmitted by mosquitoes of the Culex genus (1).  The RNA virus belongs to the Flaviviridae family, which also includes the virus that causes dengue, yellow fever and zika (2). WNV is classified as Baltimore Group IV, a single-stranded, positive-sequence RNA virus (ssRNA+). There are two main seropositive strains, lineage 1 and lineage 2, both of which are pathogenic to humans and animals (3).

WNV is not transmitted by direct contact between people, although it can be transmitted from mother to fetus or by blood transfusion (4). The virus’s final hosts are horses and humans (5). Risk factors include immunosuppression and chronic diseases such as diabetes, heart and kidney failure, and highly invasive viral strains (6).  The incubation period for WNV in humans ranges from approximately 2 to 14 days, although it can sometimes reach 21 days (7).  Diagnosis is made in serum and cerebrospinal fluid (CSF) by detecting specific anti-WNV IgM immunoglobulins (8). The methods used for detection are ELISA and Northern blot analysis. RNA can be identified with polymerase chain reaction (PCR) (9).

WNV measures 40–60 nm in diameter, has icosanoidal symmetry, and is surrounded by an envelope containing a lipid peri-capsid derived from the host membrane. The single-stranded RNA is positive-sense, approximately 11 Kb in length, and encodes a single multiplex protein, which is subsequently cleaved into 10 proteins: 3 structural proteins, 1 C capsid, which forms the internal core of the virion, 2 membrane-bound prM/M proteins, which protect the E protein during assembly, and 3 E envelope proteins, which mediate attachment and fusion with the host cell (10).  The other proteins are non-structural (NS1–NS5) and are involved in RNA replication, immune evasion, and viral assembly.

WNV replicates by attaching to the host cell via the E protein and interacting with specific cellular receptors (11). The viral receptor mediates endocytosis through fusion of the envelope with the endosomal membrane and release of the RNA into the cytoplasm (12). Viral replication occurs in the endoplasmic reticulum through a replication complex composed of NS proteins and the assembly of new virions in the endoplasmic reticulum, with maturation in the Golgi apparatus (13). Virions are released by exocytosis and can infect birds and Culex mosquitoes.

DISCUSSION

WNV disease is not very common, but it can be severe in the neuroinvasive form, which is characterized by three main types: meningitis, encephalitis (with death), and flaccid muscle paralysis similar to polio (14). Approximately 80% of infected people infected with WNV have no symptoms, but around 20% may experience a mild form with fever, headache, fatigue, and mild nausea. The most severe form is neuroinvasive with higher risk for the elderly or immunocompromised. This neuroinvasive form of WNV is characterized by viral invasion of the central nervous system (CNS) (15).

When WNV becomes neuroinvasive, it can affect the meninges and cause meningitidis, producing brain inflammation with fever, photophobia, and nausea. WNV can also cause encephalitis, leading to inflammation, mental changes, convulsions, confusion, and disorientation (16). Additionally, WNV may cause acute flaccid paralysis resembling polio, with asymmetric weakness and paralysis, reduced reflexes, and impaired sensation (14).

Inflammatory damage to the CNS is highlighted with neuroimaging using magnetic resonance imaging (MRI) (17). As is usually the case with viruses, there are no specific treatments, but supportive care is used, such as the use of antipyretics and anti-inflammatories, as well as anticonvulsants, respiratory support, and hydration (18).

WNV reaches the CNS through increased blood-brain barrier (BBB) permeability (19). In the meninges, particularly in the microglia, the virus induces inflammatory cytokines such as IL-1, TNF, and IL-6, which cause endothelial cell dysregulation (20). The dysregulated BBB allows peripheral blood monocytes to pass through, which reach the CNS and contribute to the inflammatory process mediated by inflammatory mediators, including cytokines (21). Additionally, macrophages activated by phagocytosis act as reservoirs for the virus, which is subsequently transported to the brain (22).  WNV invades peripheral nerve endings and microglia, where it also replicates in endothelial cells, exacerbating the disease (23). Neurons are the virus’s primary target cells, particularly those in the brainstem, cerebellum, hippocampus, and spinal cord (24). WNV-induced damage manifests as an inflammatory neuropathy with activation of astrocytes (25).

Prevention is achieved with mosquito-repellent insecticides and body protection. Careful monitoring of endemic areas could drastically reduce transmission of the virus through its vector (26). WNV is sensitive to lipid solvents (such as ether and chloroform), heat, and acidic pH, but is resistant to low temperatures and can survive prolonged freezing (27).

CONCLUSIONS

WNV transmitted by the Culex mosquito can affect humans and cause systemic infection. The virus is not transmitted from human to human but only through the bite of an infected mosquito. The most severe form of WNV disease is neuroinvasive and, when infected, the CNS produces inflammatory proteins, including cytokines that aggravate the disease.

Conflict of interest

The authors declare that they have no conflict of interest.

REFERENCES

1. Jani C, Kakoullis L, Ben Abdallah N, et al. West Nile virus: another emerging arboviral risk for travelers? Current infectious disease reports. 2022;24(10):117-128. doi:https://doi.org/10.1007/s11908-022-00783-4
2. Rebollo B, Pérez T, Camuñas A, et al. A monoclonal antibody to DIII E protein allowing the differentiation of West Nile virus from other flaviviruses by a lateral flow assay. Journal of Virological Methods. 2018;260:41-44. doi:https://doi.org/10.1016/j.jviromet.2018.06.016
3. Mencattelli G, Silverj A, Iapaolo F, et al. Epidemiological and Evolutionary Analysis of West Nile Virus Lineage 2 in Italy. Viruses. 2022;15(1):35-35. doi:https://doi.org/10.3390/v15010035
4. Campbell GL, Marfin AA, Lanciotti RS, Gubler DJ. West Nile virus. The Lancet Infectious Diseases. 2002;2(9):519-529. doi:https://doi.org/10.1016/s1473-3099(02)00368-7
5. Baldon L, Mendonça S de, Santos E, et al. Suitable Mouse Model to Study Dynamics of West Nile Virus Infection in Culex quinquefasciatus Mosquitoes. Tropical Medicine and Infectious Disease. 2024;9(9):201-201. doi:https://doi.org/10.3390/tropicalmed9090201
6. Murray KO, Baraniuk S, Resnick MB, et al. Risk factors for encephalitis and death from West Nile virus infection. Epidemiology and infection. 2006;134(6):1325-1332. doi:https://doi.org/10.1017/s0950268806006339
7. Vollans M, Day J, Cant S, et al. Modelling the temperature dependent extrinsic incubation period of West Nile Virus using Bayesian time delay models. Journal of Infection. 2024;89(6):106296-106296. doi:https://doi.org/10.1016/j.jinf.2024.106296
8. Karim SU, Bai F. Introduction to West Nile Virus. Methods in molecular biology. 2022;2585:1-7. doi:https://doi.org/10.1007/978-1-0716-2760-0_1
9. Li W, Brinton MA. The 3′ Stem Loop of the West Nile Virus Genomic RNA Can Suppress Translation of Chimeric mRNAs. Virology. 2001;287(1):49-61. doi:https://doi.org/10.1006/viro.2001.1015
10. Hernandez-Triana LM, Jeffries CL, Mansfield KL, Carnell G, Fooks AR, Johnson N. Emergence of West Nile Virus Lineage 2 in Europe: A Review on the Introduction and Spread of a Mosquito-Borne Disease. Frontiers in Public Health. 2014;2. doi:https://doi.org/10.3389/fpubh.2014.00271
11. Keramatnejad M, DeWolf C. A biophysical study of tear film lipid layer model membranes. Biochimica et Biophysica Acta (BBA) – Biomembranes. 2022;1865(3):184102. doi:https://doi.org/10.1016/j.bbamem.2022.184102
12. Smit J, Moesker B, Rodenhuis-Zybert I, Wilschut J. Flavivirus Cell Entry and Membrane Fusion. Viruses. 2011;3(2):160-171. doi:https://doi.org/10.3390/v3020160
13. Tseng AC, Nerurkar VR, Neupane KR, Kae H, Kaufusi PH. Potential Dual Role of West Nile Virus NS2B in Orchestrating NS3 Enzymatic Activity in Viral Replication. Viruses. 2021;13(2):216. doi:https://doi.org/10.3390/v13020216
14. Petersen LR, Brault AC, Nasci RS. West Nile Virus: Review of the Literature. JAMA. 2013;310(3):308. doi:https://doi.org/10.1001/jama.2013.8042
15. Marshall EM, Bauer L, Nelemans T, et al. Differential susceptibility of human motor neurons to infection with Usutu and West Nile virus. Journal of Neuroinflammation. 2024;21(1). doi:https://doi.org/10.1186/s12974-024-03228-y
16. Kramer LD, Li J, Shi PY. West Nile virus. The Lancet Neurology. 2007;6(2):171-181. doi:https://doi.org/10.1016/s1474-4422(07)70030-3
17. Vidaña B, Johnson N, Fooks AR, Sánchez‐Cordón PJ, Hicks DJ, Nuñez A. West Nile Virus spread and differential chemokine response in the central nervous system of mice: Role in pathogenic mechanisms of encephalitis. Transboundary and Emerging Diseases. 2019;67(2):799-810. doi:https://doi.org/10.1111/tbed.13401
18. Srivastava R, Ramakrishna C, Cantin E. Anti-inflammatory activity of intravenous immunoglobulins protects against West Nile virus encephalitis. Journal of General Virology. 2015;96(6):1347-1357. doi:https://doi.org/10.1099/vir.0.000079
19. Roe K, Orillo B, Verma S. West Nile Virus-Induced Cell Adhesion Molecules on Human Brain Microvascular Endothelial Cells Regulate Leukocyte Adhesion and Modulate Permeability of the In Vitro Blood-Brain Barrier Model. Toborek M, ed. PLoS ONE. 2014;9(7):e102598. doi:https://doi.org/10.1371/journal.pone.0102598
20. Zidovec-Lepej S, Vilibic-Cavlek T, Barbic L, et al. Antiviral Cytokine Response in Neuroinvasive and Non-Neuroinvasive West Nile Virus Infection. Viruses. 2021;13(2):342. doi:https://doi.org/10.3390/v13020342
21. Constant O, Maarifi G, Barthelemy J, et al. Differential effects of Usutu and West Nile viruses on neuroinflammation, immune cell recruitment and blood–brain barrier integrity. Emerging Microbes & Infections. 2023;12(1). doi:https://doi.org/10.1080/22221751.2022.2156815
22. McMillan RE, Wang E, Carlin AF, Coufal NG. Human microglial models to study host–virus interactions. Experimental neurology. 2023;363:114375-114375. doi:https://doi.org/10.1016/j.expneurol.2023.114375
23. Zukor K, Wang H, Hurst BL, et al. Phrenic nerve deficits and neurological immunopathology associated with acute West Nile virus infection in mice and hamsters. Journal of NeuroVirology. 2016;23(2):186-204. doi:https://doi.org/10.1007/s13365-016-0488-6
24. Fulton CDM, Beasley DWC, Bente DA, Dineley KT. Long-term, West Nile virus-induced neurological changes: A comparison of patients and rodent models. Brain, Behavior, & Immunity – Health. 2020;7:100105. doi:https://doi.org/10.1016/j.bbih.2020.100105
25. Verma S, Kumar M, Nerurkar VR. Cyclooxygenase-2 inhibitor blocks the production of West Nile virus-induced neuroinflammatory markers in astrocytes. Journal of General Virology. 2010;92(3):507-515. doi:https://doi.org/10.1099/vir.0.026716-0
26. Singh P, Khatib MN, Ballal S, et al. West Nile Virus in a Changing Climate: epidemiology, pathology, advances in diagnosis and treatment, vaccine designing and control strategies, emerging public health challenges – a comprehensive review. Emerging Microbes & Infections. 2024;14(1):2437244. doi:https://doi.org/10.1080/22221751.2024.2437244
27. Remington KM, Trejo SR, Buczynski G, et al. Inactivation of West Nile virus, vaccinia virus and viral surrogates for relevant and emergent viral pathogens in plasma-derived products. Vox Sanguinis. 2004;87(1):10-18. doi:https://doi.org/10.1111/j.1423-0410.2004.00530.x