West Nile Virus

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Introduction   

West Nile Virus (WNV) is a zoonotic, mosquito-borne flavivirus and a member of the Flaviviridae family, responsible for a spectrum of diseases ranging from mild febrile illness to severe, lethal neuroinvasive conditions (1)(3)(4). Researchers isolated WNV in 1937 from a febrile patient in the West Nile Province of Uganda, identifying it as causing mild, subclinical infections (2). WNV has emerged as a significant public health concern, causing outbreaks in humans, horses, birds, and other wildlife across all continents except Antarctica (2). 

WNV infection displays diverse clinical manifestations. Most individuals show no symptoms, but 1 in 4 develops febrile symptoms resembling a viral syndrome (3). About 1 in 150 of those infected develop neuroinvasive diseases with severe neurological deficits, such as encephalitis (4).  

Infected Culex mosquitoes transmit the virus through bites (5). Other modes of WNV transmission include blood transfusion, organ transplantation, intrauterine transfer, and breastfeeding (5). Researchers identify the virus in animals, including birds, horses, reptiles, and rodents, complicating its epidemiology (6).  

The global spread of WNV began in the 1990s, expanding from its origins in Africa to Europe, Asia, and North America (1)(2)(7). The virus exists in many parts of the world, and globalization and climate change drive infectious disease outbreaks (10). Clinicians face challenges diagnosing WNV infection because of its variable clinical presentation and rarity. The disease can progress to devastating and fatal outcomes, making early recognition and supportive management crucial. In recent years, the spread of West Nile Virus (WNV) has emerged as a significant public health concern, with outbreaks reported in several European countries, including Italy, Hungary, Romania, and Greece.  

During the 2023 transmission season, by December 2023, European countries reported 709 human WNV cases and 67 deaths, including cases in Italy, Greece, Romania, France, Hungary, Spain, and Germany (17)(18). Recent climate conditions and the introduction of new lineage 1 WNV genetic variants drive the increased spread of WNV in Europe (17) (19). 

No specific antiviral treatment or licensed vaccine exists for human use, complicating efforts to control the virus (8). Preventative measures, such as insect repellents, permethrin-treated clothing, and mosquito control programs, remain the cornerstone of public health interventions (9). Effective management of WNV infections requires an interprofessional approach involving emergency medicine physicians, infectious disease specialists, critical care teams, pharmacists, and specialty-trained nurses. 

Despite extensive research into the pathogenesis, epidemiology, and potential vaccine development, significant gaps in knowledge remain. This review provides an updated overview of the biology, pathobiology, epidemiology, diagnostic methods, control strategies, and “One Health” implications of WNV, highlighting the urgent need for continued efforts in prevention and management to mitigate the impact of this re-emerging zoonotic threat (2). 

Transmission of West Nile Virus (WNV) 

Biological vectors (mosquitoes) transmit West Nile Virus (WNV) and function as both vectors and intermediate hosts (11). Mosquitoes amplify the virus before transferring it to definitive hosts (11). These vectorial and intermediary roles underscore the critical contribution of mosquitoes to the WNV transmission cycle. Documented modes of transmission include organ transplants, needlestick injuries, hemodialysis, and blood transfusions (5). 

Blood transfusions and solid organ transplants pose significant risks, as the virus can remain viable in solid organs even when serology results are negative (12) (13). Reports document WNV transmission through whole blood and components, including red blood cells, plasma, and platelets (14). Researchers identify other non-vectorial transmission beyond mosquito bites, including an oral-fecal route of WNV transmission in American alligators and saltwater crocodiles (2).  

Contact transmission occurs in commercial geese farming through behaviors such as cannibalism and feather pecking among infected birds (15). Reports indicate rare cases of transplacental transmission in humans and possible breastfeeding transmission (2)(16). Experts hypothesize that aerosol transmission of West Nile Virus (WNV) may occur among animal handlers and laboratory workers exposed to infected materials.  

Workers at higher risk include military personnel, veterinarians, agricultural workers, farmers, and laboratory staff in contact with infected fluids or aerosols (17). Identifying these high-risk groups enables occupational physicians to implement active surveillance, enhancing our understanding of WNV epidemiology and informing tailored preventive strategies to reduce disease burden in affected areas. 

Behavioral and underlying health factors can influence the risk of West Nile Virus (WNV) infection and associated diseases. Research identifies alcohol abuse as a significant risk factor for West Nile Virus (WNV) infection (2)(20). Hypertension, cerebrovascular disease, chronic renal disease, and diabetes mellitus increase susceptibility (2)(20). 

These diverse modes of transmission highlight the complexity of WNV spread and the importance of understanding biological and behavioral risk factors to manage and prevent outbreaks. 

West Nile Virus (WNV) Life Cycle 

The life cycle of West Nile Virus (WNV) is complex, involving multiple key players: virus reservoirs, mosquito vectors, and final or incidental hosts. Birds serve as primary reservoirs, capable of harboring the virus without displaying clinical disease (4)(21). Mosquitoes serve as vectors and intermediate hosts, replicate the virus, and transmit it to final hosts, such as humans or other vertebrates, during blood meals (4)(5). 

Dynamics of Transmission within the Mosquito Host 

Competent mosquito vectors acquire the virus by feeding on a viremic vertebrate host (11). Once ingested, WNV reaches the mosquito’s midgut, replicating and spreading to the salivary glands (4)(24). During subsequent blood meals, mosquitoes transmit the virus to the final host when their saliva contains a viral concentration exceeding 10⁴ TCID50/mL (22). The saliva facilitates virus delivery and contains proteins that interfere with the host’s T-cell immune response, aiding initial immune evasion and viral dissemination (22)(23). WNV does not cause apparent disease in mosquitoes, ensuring their viability as effective vectors (4)(20). 

Infection of Vertebrate Hosts 

Vertebrate hosts, including reservoirs and incidental hosts, are infected when mosquitoes inject saliva while probing for blood vessels (4)(21). In addition to its anticoagulant properties, mosquito saliva aids viral entry and immune evasion. Once inside the vertebrate host, WNV infects cells through receptor-mediated endocytosis. Dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin receptor (DC-SIGNR) is the primary receptor mediating WNV cell entry (22).  

Mannose receptors and glycosaminoglycans also play roles. After binding to the receptor, the virus enters the host cell’s endosomal vesicles, where acidic conditions trigger conformational changes in the viral envelope protein (E protein), facilitating membrane fusion and release of the viral nucleocapsid and RNA into the cytoplasm (25). 

Viral Replication and Release 

WNV RNA undergoes replication in the host cell cytoplasm. Synthesized viral particles acquire a lipid envelope by budding into the lumen of the endoplasmic reticulum (ER) (25). During exocytosis, furin cleaves prM proteins on immature virions, producing mature infectious particles that leave the cell and infect additional cells (22). 

Amplification in Crocodilians 

Most final hosts, such as humans and horses, cannot sustain sufficient viremia for further transmission, but crocodilians sustain viremia and contribute to transmission (4)(5). Crocodilians amplify the virus, contributing to its transmission dynamics in their ecosystems (26). 

Behavioral and Immune Considerations 

During vector-mediated infection, WNV infects cutaneous macrophages and dendritic cells through DC-SIGN receptors, while its systemic spread in the host occurs independently of these receptors (4)(27). This multifaceted life cycle highlights WNV’s evolutionary adaptations for efficient replication, immune evasion, and transmission across diverse hosts. 

Epidemiology  

Researchers first identified West Nile Virus (WNV) in Uganda in 1937. It caused mild illnesses until 1999, when cases appeared in the Western Hemisphere, revealing its global impact (2). The New York outbreak caused 62 cases of encephalitis and seven deaths (28). Earlier outbreaks involved minor illnesses, but the virus has caused severe neurological diseases since the mid-1990s (1)(2)(7). 

Clinical Presentation in Humans 

The clinical spectrum of WNV infection varies. 80% of individuals experience no symptoms, while 20% develop West Nile fever, characterized by fever above 38°C, headache, lethargy, depression, and maculopapular or petechial rashes (4). While most individuals with West Nile virus-related febrile illness recover, fatigue and weakness may persist for weeks or months (4). 1 in 150 individuals infected with West Nile virus develops severe illness involving the central nervous system, such as encephalitis or meningitis (2)(4).  

Symptoms of neuroinvasive disease include nuchal rigidity, photophobia, flaccid paralysis, and myasthenia, with a mortality rate approaching 10% (4)(29). Patients experience gastrointestinal symptoms, including nausea, vomiting, diarrhea, and anorexia, along with lymphadenopathy and hepatosplenomegaly (2)(4). Children, the elderly, and individuals with chronic conditions are at higher risk for severe disease.  

Clinical Presentation in Animals 

• Birds: Susceptible avian species show lethargy, ataxia, head tremors, seizures, leg paralysis, and weight loss (30). 

• Reptiles: Symptoms in reptiles range from subclinical in saltwater crocodiles to severe gastrointestinal and neurological diseases in American alligators. Neurological signs include unbalanced swimming, head tilt, and muscle tremors, while gastrointestinal symptoms include bloating and anorexia (2)(31). 

• Snakes: Common signs include aggression, cachexia, immobility of the caudal body, and weakness (2)(32). 

Case Study: West Nile Virus (WNV) Neuroinvasive Disease 

Patient Information: 

• Name: John Doe 
• Age: 64 years 
• Sex: Male 
• Occupation: Retired teacher, recreational gardener 
• History of Travel: A recent visit to a rural area in the Midwest United States during late summer 
• Presenting Complaint: Fever, confusion, and severe headache 

Clinical Presentation: 

John presented to the emergency department with complaints of fever (39.4°C), severe headache, nausea, and confusion for three days. His family reported a recent history of fatigue, lethargy, and decreased appetite. He also experienced mild muscle weakness and photophobia. His wife noted that he had spent considerable time gardening outdoors without insect repellent. 

Vital Signs: 

• Temperature: 39.4°C 
• Heart Rate: 129 beats/min (tachycardia) 
• Respiratory Rate: 22 breaths/min 
• Blood Pressure: 128/86 mmHg 
• Oxygen Saturation: 96% on room air 

 Physical Examination: 

• General Appearance: Alert but disoriented to time and place 
• Neurological Exam: 
• Positive for nuchal rigidity 
• Decreased motor strength in bilateral lower extremities (4/5) 
• Hyperreflexia in the lower extremities 
• No focal deficits were observed 
• Positive Brudzinski’s and Kernig’s signs 
• Skin Examination: Maculopapular rash noted on the trunk 
• Ophthalmologic Exam: Mild conjunctival injection with no evidence of multifocal chorioretinitis 

 Laboratory Findings: 

• Complete Blood Count (CBC): 
  • WBC: 12.8 x 10⁹/L (elevated) 
  • Hemoglobin: 14.1 g/dL 
  • Platelets: 180 x 10⁹/L (normal) 
• Basic Metabolic Panel (BMP): 
  • Sodium: 129 mmol/L (hyponatremia) 
  • Potassium: 4.2 mmol/L 
  • Creatinine: 1.0 mg/dL 
• Cerebrospinal Fluid (CSF) Analysis: 
  • WBC: 78/mm³ (lymphocytic predominance) 
  • Protein: 120 mg/dL (elevated) 
  • Glucose: 58 mg/dL (normal) 
  • IgM antibodies for WNV: Positive by ELISA 
  • Viral PCR: Positive for WNV RNA 

 Imaging Studies: 

• CT Brain (Initial): Normal, no acute findings 
• MRI Brain (Day 3): Hyperintense signals in the basal ganglia and thalamus, consistent with neuroinvasive WNV (33) 

 Diagnosis: 

• Neuroinvasive West Nile Virus (WNV) infection presenting as meningoencephalitis. 

 Treatment Plan: 

1. Supportive Care: 
2. Intravenous fluids to correct hyponatremia 
3. Antipyretics for fever management 
4. Pain management for headache 
5. Neurologic Monitoring: 
6. Admitted to the ICU for close observation and prevention of complications 
7. Prophylaxis for deep vein thrombosis (DVT) with subcutaneous heparin 
8. Regular repositioning to prevent pressure sores 
9. Rehabilitation Plan: 
10. Initiated physical and occupational therapy to address motor deficits 
11. Cognitive treatment for improving memory and orientation 

Outcome and Follow-Up:

After 14 days in the hospital, the team discharged John to a rehabilitation center for physical and cognitive therapy. At his one-month follow-up, he showed weakness in his lower extremities and attention deficits. His care team emphasized continued rehabilitation and scheduled further neurological evaluations to monitor for long-term sequelae. 

Factors Influencing Susceptibility to West Nile Virus 

Intrinsic and extrinsic factors play critical roles in determining the risk of West Nile Virus (WNV) infection. Age is a significant inherent factor, with susceptibility increasing by 1.5 times for every decade of life. Individuals over 75 years are vulnerable due to age-related declines in immune function, such as reduced macrophage activity and impaired type I interferon responses (34).  

Gender also influences susceptibility, with males at higher risk (35). Pre-existing conditions like cancer, cardiovascular disease, diabetes, and immunosuppression elevate the risk of severe outcomes (34). Immunosuppressed individuals are vulnerable, facing a 40-fold higher likelihood of severe complications (1)(2). 

Environmental and ecological influences also contribute to WNV transmission. Urban settings are associated with outbreaks due to the behavior of mosquito species such as Cx. pipiens and Cx. quinquefasciatus, which thrive in peri-domestic environments (2)(36). In rural areas, agricultural practices like irrigation create breeding grounds for mosquitoes, while habitat destruction forces reservoirs and vectors into closer contact with humans (2)(37). 

Transmission and Outbreak Trends 

The mosquito life cycle and bird-mosquito amplification cycles drive outbreaks, with cases peaking in late summer and fall (2)(38). In warmer climates, infections may occur year-round (38). From 1999 to 2015, the U.S. reported 44,000 cases of WNV, with over 20,000 involving neuroinvasive disease (39). Neuroinvasive cases vary by year, ranging from 386 to 2,946 per annum (40). Surveys and blood donor screening suggest a neuroinvasive disease rate of 0.5% among infected individuals and an infection rate of 10% in outbreak areas, extrapolating to 3 to 5 million estimated cases worldwide (41). 

WNV remains endemic in many regions, including Africa, the Middle East, Australia, Europe, and Asia. Endemic and non-endemic areas report outbreaks, highlighting the virus’s growing global reach. The interplay of environmental, demographic, and biological factors continues to shape the dynamics of WNV transmission and its impact on public and animal health

Pathophysiology 

Mosquitoes transmit West Nile Virus (WNV) during blood meals, introducing infected saliva into the host (5). Following transmission, the virus undergoes an initial replication phase in dermal dendritic cells and keratinocytes at the entry site (24). The early phase transitions to a visceral-organ dissemination phase (24). The virus replicates in draining lymph nodes, enters the bloodstream, and spreads to visceral organs (24).  

The final phase involves the virus reaching the central nervous system (CNS) (43). These include direct crossing of the blood-brain barrier, passive transport through endothelial cells, migration of infected macrophages across the blood-brain barrier, or retrograde axonal transport (42)(43). Once in the CNS, the virus induces significant inflammation, leading to neuronal loss in the gray matter of the spinal cord and brainstem (42)(43).  

Etiology 

Infected mosquitoes from the Culex species transmit West Nile Virus (WNV) to humans through bites (1)(4). In addition to humans, WNV can infect many hosts, including birds, horses, dogs, and other mammals (11). Wild birds serve as the primary reservoirs, facilitating viral amplification and perpetuation of the transmission cycle (11). Humans are incidental dead-end hosts because their low and transient viremia fails to sustain further transmission (44).  

Mosquito bites transmit the virus, but infected donor blood, organ transplants, breast milk, and transplacental routes also transmit it in rare cases. Around 1% of infected individuals develop severe symptoms, with neurological complications being the most common (5)(11).  

History & Physical  

The West Nile Virus (WNV) infection incubation period ranges from 2 to 14 days (3). Symptoms last 5 to 7 days, with fever present in one-quarter of cases (3). The clinical presentation is often mild, characterized by symptoms such as myalgia, malaise, and low-grade fever. Additional symptoms may include headache, eye pain, vomiting, anorexia, and, in up to 50% of cases, a maculopapular rash on the trunk that appears during defervescence (1)(2). 

In rare cases, WNV can cause severe neurologic complications, including significant muscle weakness, altered mental status, seizures, and flaccid paralysis (1)(2). These patients often present with signs of encephalitis or meningitis, which can progress, necessitating intensive care unit (ICU) management (45). Despite aggressive supportive care, the mortality rate for neuroinvasive WNV infection remains high. 

Epidemiology and Typical Course of Illness 

Most individuals with WNV have a history of travel to an area where the virus is endemic. Endemic regions span multiple continents, as discussed in the epidemiology section. The typical infection course includes fever lasting around 5 days, headache up to 10 days, and fatigue that can persist for a month or longer (3).

Laboratory Findings and Diagnosis

Routine laboratory tests in WNV infection may show leukocytosis and other nonspecific findings (46). Serological testing detects WNV IgM antibodies in blood or cerebrospinal fluid (CSF) using enzyme-linked immunosorbent assay (ELISA) for definitive diagnosis (46). The plaque reduction neutralization test (PRNT) distinguishes serologic cross-reactions with other flaviviruses (47).

In neuroinvasive cases, lumbar puncture can reveal findings consistent with viral meningitis, including elevated protein and leukocyte levels in the CSF (46). Neutrophils dominate early in the disease and transition to lymphocyte predominance, while glucose levels stay normal (46)(47). Hyponatremia is another common finding in CNS involvement (46).

Imaging Studies 

Neuroimaging is unremarkable in the initial stages of neuroinvasive WNV. Computed tomography (CT) of the brain often shows no acute abnormalities (33). However, magnetic resonance imaging (MRI) may reveal abnormalities associated with neuroinvasive disease, often weeks after the acute phase (33). 

This comprehensive approach to understanding WNV clinical presentation, diagnostic tools, and testing highlights the importance of early recognition and targeted diagnostics in cases with potential neuroinvasive involvement. 

Differential Diagnosis 

Diagnosing West Nile Virus (WNV) infection in clinical settings relies on clinical examination, laboratory testing, and, in some cases, post-mortem examination. However, diagnosis can be challenging due to the absence of pathognomonic clinical signs and the overlap of symptoms with other diseases. 

Clinical Examination 

In humans, clinical diagnosis is based on symptoms such as acute fever, anorexia, nausea, vomiting, eye pain, headache, myalgia, rash, lymphadenopathy, and arthralgia (48). Multifocal chorioretinitis identifies severe WNV infection, prompting ophthalmological examination in suspected cases (49).  

However, clinical diagnosis alone is often presumptive in non-endemic regions, where other infectious diseases with similar clinical presentations may be more common. A travel history to endemic areas plays a vital role in diagnosing regions where diseases like malaria mimic one another (1)(4). 

Laboratory-Based Diagnostics 

Serological diagnosis for West Nile Virus (WNV) involves detecting IgM and IgG antibodies, which often appear 3–7 days post-exposure (46). IgM antibodies can persist for extended periods, up to two years in some cases (e.g., horses), limiting their diagnostic utility in chronic cases (46).  

Blocking ELISA is a reliable and species-independent tool that measures the ability of patient serum antibodies to inhibit the binding of monoclonal antibodies against NS1 and E protein epitopes (46). However, this method may exhibit cross-reactivity with other flaviviruses, such as the Murray Valley encephalitis and Alfuy virus (50).  

Virus neutralization tests (VNT) are the gold standard due to their specificity. They enable the detection and quantification of neutralizing antibodies (51). However, VNTs require considerable time, often up to a week, and prohibitive costs limit their widespread use. 

Molecular diagnostics, including reverse transcription polymerase chain reaction (RT-PCR) and quantitative RT-PCR (qRT-PCR), are sensitive and specific methods for detecting WNV (46). These techniques target conserved genome regions, such as the NS5 or E protein, to identify WNV strains. qRT-PCR offers an additional advantage of quantifying viral genomes through fluorescence monitoring (52).  

However, RT-PCR may detect RNA from killed-virus vaccines, necessitating complementary methods like virus isolation or primers targeting specific viral regions to distinguish vaccine RNA from active infections (52). Molecular testing focuses on analyzing serum or cerebrospinal fluid (CSF) samples. 

Pathological examination remains a valuable diagnostic tool in research and post-mortem investigations. This approach identifies macroscopic and microscopic lesions and detects viral antigens in tissue sections using immunohistochemistry (IHC). IHC targeting NS1 or NS3 proteins provides definitive evidence of viral replication in tissues (46)(52). The utility of this method decreases due to the invasive sample collection process and the lack of specific antibodies. 

Rapid diagnostic tools like the immunochromatographic assay RapidWN™ detect WNV IgM antibodies in human plasma or serum (46). This cost-effective, user-friendly test is well-suited for low-resource settings, as it does not require specialized equipment or extensive training. Similar rapid diagnostic tools are not yet available for veterinary use, highlighting the need for affordable and accessible diagnostic options across human and animal health domains (46). 

The clinical presentation of WNV infection overlaps with many other conditions, necessitating a broad differential diagnosis that includes: 

• Viral Infections: Varicella-zoster virus, herpes simplex virus type 1, St. Louis encephalitis (cross-reactivity with flavivirus serology), enteroviruses, dengue virus, and Japanese encephalitis (20). 
• Bacterial Infections: Bacterial meningitis (20). 
• Tickborne Diseases: Lyme disease, ehrlichiosis, anaplasmosis, Rocky Mountain spotted fever, and Powassan virus (53). 

Careful travel history, clinical evaluation, and comprehensive testing are essential for distinguishing WNV from these conditions. Despite advancements in serological and molecular diagnostics, limitations persist in the availability of rapid, affordable tools for early detection. Developing user-friendly diagnostic methods for human and veterinary use remains a priority in improving WNV management and control. 

Treatment 

The treatment of West Nile Virus (WNV) infection is primarily supportive, as no specific antiviral therapy has demonstrated apparent efficacy (8). Researchers have explored various agents, including interferon, ribavirin, and intravenous immunoglobulin, but the evidence remains limited (54). 

Management is often outpatient for individuals with mild cases and focuses on symptom relief. These patients have an excellent prognosis. In contrast, patients with severe neurologic symptoms usually require intensive care unit (ICU) management and may face a prolonged recovery, high mortality, and early disability (55).  

Long-term physical and occupational therapy at rehabilitation centers can address residual neurologic deficits. These deficits may involve gross motor, fine motor, and cognitive impairments, some of which can take months or years to recover, while others may be permanent (55). 

In central nervous system (CNS) involvement cases, patients are at substantial risk for complications due to prolonged immobility. West Nile Virus (WNV) affects anterior horn cells, leading to a poliomyelitis-like syndrome, and is the most common underlying cause of paralysis associated with WNV infection (56). Resulting issues include pressure sores, aspiration pneumonia, and deep vein thrombosis (DVT). Prophylactic measures to prevent these complications, such as regular repositioning, aspiration precautions, and DVT prophylaxis, are essential components of comprehensive care. 

Documented sequelae include Parkinsonian tremors, poliomyelitis, meningitis, and cognitive impairments, affecting more than one-third of confirmed cases (55). The virus’s vestibular tropism causes hearing loss, leading to chronic vestibulocochlear neuritis and functional impairment (57).  

Experimental studies in mice have demonstrated WNV infection in spiral ganglion neurons of the inner ear, highlighting its potential for long-term cranial nerve damage (57). Persistent damage to other cranial nerves, such as the ocular nerve, occurs for up to three years post-recovery (55). Chronic retinopathy, contractures of extremities, severe dysphonia, and movement disorders are other reported complications (2). Neurologic damage to the cerebral cortex is linked to attention deficits, memory loss, concentration issues, anxiety, depression, and abnormal gait (55)(58)(59). Further research must explore potential links between WNV infection and chronic neurological disorders, including Alzheimer’s disease, dementia, multiple sclerosis, and Parkinson’s disease (60). 

Persistence of WNV Infection 

Evidence suggests that WNV can persist in host species, including humans, birds, and mammals (2). Experimental studies have demonstrated persistent viruria in hamsters for up to 52 days post-infection, with viral antigens detected in kidney epithelial cells (2)(61). Infected hamsters have also shown WNV persistence in the brain for up to 89 days, leading to neuron dysfunction and poliomyelitis-like syndromes (2)(61).  

Infectious WNV and its RNA remain detectable in mice for four and six months after infection (2)(62). In monkeys, intracranial infection resulted in prolonged viral persistence, while human studies have detected WNV RNA in urine samples for over six years post-infection (2)(63). 

The persistence of WNV in hosts beyond the viremic period poses significant epidemiological and public health concerns, necessitating further investigation into its mechanisms and implications. 

Immunity and Reinfection 

There have been no reported cases of WNV reinfection in clinical or experimental settings (2). Primary infection confers lifelong immunity (2)(4). Studies confirm the persistence of WNV IgM and IgG antibodies for up to three years post-infection, with neutralizing antibodies present in 94.4% of seropositive blood donors five years after infection (2)(64). These findings suggest that long-lasting immunity protects against reinfection (2)(64). 

Coinfections with Other Pathogens 

Coinfections with WNV and other pathogens are known in areas with high mosquito activity (2)(65). Coinfections can result from overlapping geographic distributions and shared vectors. Researchers documented coinfections of WNV with malaria in birds and humans (65). While some studies suggest an inverse association between WNV and avian malaria, others report a direct positive correlation between WNV and human Plasmodium falciparum cases (65).  

Natural coinfections of WNV with other arboviruses, including dengue virus (DENV), chikungunya virus (CHIKV), and Japanese encephalitis virus (JEV), occurred (2)(66). Reports confirm WNV and JEV coinfections in encephalitis patients, and WNV and Toscana virus (TOSV) coinfections occur in febrile patients in Türkiye (2)(67). Researchers have noted a coinfection of poxviruses in American crows and Halicephalobus gingivalis in humans (2)(68).  

Vector and Host Interactions 

Interactions between WNV and endosymbionts, such as Wolbachia, can influence vector competence. While Wolbachia reduces the transmission of DENV and CHIKV in Aedes aegypti, its impact on WNV varies. Studies have shown that Wolbachia can enhance WNV infection in Culex tarsalis mosquitoes but impair transmission in Culex quinquefasciatus (69). Insect-specific flaviviruses (ISFs), such as Palm Creek and Bamaga viruses, suppress WNV replication and provide potential options for biologically controlling pathogenic flaviviruses (70).  

Public Health Implications 

The persistence, immunity, and coinfection dynamics of WNV raise significant public health concerns. Understanding these phenomena and their interactions with other pathogens and vectors could inform strategies for controlling WNV and other flaviviruses. Further research into the long-term impacts of WNV infection, including its potential link to chronic neurological conditions, remains a critical public health priority. 

Conclusion

West Nile Virus (WNV) represents a complex and growing public health concern characterized by diverse transmission pathways, clinical presentations, and global distribution. The virus’s ability to spread through mosquito vectors, blood transfusions, organ transplants, and rare non-vectorial modes underscores the multifaceted nature of its transmission.

Clinical manifestations range from asymptomatic infections to severe neuroinvasive diseases, which can lead to long-term neurological deficits and significant morbidity (2). The emergence of new genetic variants and environmental changes further complicates the epidemiological landscape, necessitating an integrated approach to surveillance, prevention, and management (2)(10)(38).

Despite advancements in understanding WNV pathogenesis, significant gaps remain in diagnostic capabilities, treatment options, and vaccine development. Preventive measures like vector control and personal protection remain the cornerstone of public health efforts. Collaboration among healthcare professionals, researchers, and policymakers is essential to address these challenges.

Future efforts should focus on enhancing diagnostic tools, exploring therapeutic interventions, and investigating the virus’s long-term health impacts to mitigate the burden of this re-emerging zoonotic threat.

Teaching Points:

• Neuroinvasive WNV is a rare but severe complication of WNV infection, requiring prompt diagnosis and supportive care.
• Early recognition of symptoms such as fever, headache, and neurologic changes is crucial for initiating appropriate management.
• Prevention strategies, including insect repellents and protective clothing, are critical, particularly for individuals in endemic regions.

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