West Nile Virus: Threatening Global Health as a Sequelae of the Climate Crisis
- Aashika Dupati
- 2 days ago
- 8 min read
Abstract
West Nile Virus (WNV) is an extremely debilitating and life-threatening mosquito-borne viral infection in humans, emerging as a significant public health threat across the globe. Since its discovery in Uganda, WNV has spread rapidly throughout Africa, Europe, and the Americas. The ongoing climate crisis, consisting of excessive heat and rain, has paved the way for these vector-borne diseases to prosper and spread faster than ever before, exacerbating the risk of WNV transmission. WNV can cause long-term disability and death, more severely targeting the elderly population (60 years and above) and immunocompromised individuals. This review focuses on the epidemiology, clinical features, transmission, diagnosis, prevention, and treatment of WNV through a global health lens, largely focusing on the intersection of climate change and vector-borne diseases in limiting such outbreaks.
Introduction
Public health is continuously impacted by the fast-growing infectious threat posed by vector-borne diseases. One of these threats is the West Nile Virus. West Nile is a mosquito-borne virus of the genus Flavivirus, first noted in West Nile, Uganda, in 1937 (Colpitts, T. M., et al., 2012). Rising to its height in the past 2 decades, the virus quickly became a global health concern across the world, developing into an “emerging global pathogen” (L R Petersen & J T Roehrig, 2001), marking a turning point in epidemiological profile with reported cases in every state within the United States. In addition to the U.S., WNV is widely spread throughout Africa, the Middle East, parts of Europe and Russia, South Asia, and Australia. The most commonly involved mosquito is the Culex mosquito, a genus with the unique feature of being an effective vector that feeds on birds, the main hosts of WNV. This virus also largely infects horses in addition to humans and birds (CDC, 2022). As a result of the accelerating global climate crisis, warmer temperatures, excessive and more erratic rainfall, and extended mosquito breeding cycles have paved the ideal conditions for disease spread. Together, these climate shifts feed into the multiplication of mosquito populations, and as a result, they are dramatically increasing the viral transmission potential.
Figure 1: West Nile Virus Global Impact. Pink shows areas with human WNV cases, while blue shows mosquito cases carrying WNV (Caren Chancey et al., 2015).
Clinical Features
Symptoms of West Nile Virus are not always present. Around 80% of people infected with West Nile virus don’t develop any symptoms at all. But for about one in five people infected, they may experience minor symptoms including fever, chills, sweats, vomiting, and/or diarrhea. Many people without external conditions recover within a week, while others could take months for full recovery. Unfortunately, some patients have permanent or fatal disabilities (CDC, 2022). In fewer than 1% of cases, individuals may have serious conditions leading to encephalitis or meningitis, characterized by the inflammation of the membrane surrounding the brain (CDC, 2022). Symptoms are more exacerbated in the elderly population, where there exist more age-related changes to the immune system that greatly reduce their ability to fight such viruses. These complications can lead to lifelong implications, including severe headaches, seizures, muscle weakness, and even coma. As a result, they face higher rates of heightened symptoms and long-term damage. This situation highlights the health equity gap, where populations more vulnerable to West Nile Virus have difficulty accessing healthcare and resources to maintain their well-being. This underscores the fact that addressing WNV goes beyond targeted prevention and includes support for the elderly and immunocompromised communities, bridging the health equity gap in terms of global responses to WNV and lifting some of the burden of the effects of the disease.
Transmission
Since West Nile Virus is primarily transmitted through mosquito bites, the monsoon season and warm temperatures during summer facilitate the rapid multiplication of mosquitoes, specifically the Cx. spp. Population (Paz, S., & Semenza, J. C., 2013). These favorable conditions are directly related to climate change. More specifically, rising global temperatures are creating an extended warm environment for mosquito breeding to begin in early spring and last through the fall, expanding these periods as climate change worsens. Climate-driven changes like heavier rains, more floods, and still water provide the ideal habitat for Culex mosquitoes to reproduce and contribute to a larger threat of West Nile Virus. Warmer temperature also contributes to the acceleration of the infection that affects the mosquitoes sooner, allowing for more chances to spread to humans. Together, all of these conditions increase the risk of transmission of WNV.
The Culex mosquitoes are the primary vectors of WNV due to commonly feeding off dead infected birds, who serve as the main reservoir hosts for WNV (Molaei, G. et al., 2006). The mosquitoes and birds go through a cycle of infecting each other, while the infected mosquitoes then infect humans, horses, and other mammals. However, these mammals are considered “dead-end” hosts that don’t significantly contribute to WNV transmission (CDC, 2021). On rare occasions, West Nile could spread through blood transfusions, organ transplantations, transplacental transfer, and within a lab setting (CDC, 2021).
As WNV enters the human body, it replicates right after inoculation, spreading into the lymph nodes and bloodstream. WNV causes an inflammatory process and higher levels of tumor necrosis factor-α, a cytokine (specific protein) known for signaling events within a cell, such as apoptosis, and then crosses the blood-brain barrier. WNV attacks neurons connected to the brain in gray matter, brainstem, and spinal cord, causing paralysis by damaging tissue in the process (Hayes, E. B., 2005).
Figure 2: MRI image of human brain inflammation caused by West Nile Virus (Sejvar, 2014)
Diagnosis
In patients with clinical features of West Nile virus as described above, serological and radiological studies are performed to confirm the diagnosis. Serological tests for WNV include IgG antibodies and IgM antibodies, while RT-PCR is also occasionally utilized (WHO, 2017). The presence of WNV-specific IgG antibodies shows that the patient has had an infection of WNV in the past few years. Alternatively, WNV-specific IgM antibodies can be detected in the blood of patients with an active or recent WNV infection (Mayo Clinic, 2023). High levels of IgG and IgM antibodies in the cerebrospinal fluid (CSF) can indicate possible WNV meningitis (CDC, 2023). RT- PCR testing can be done on the serum and CSF early in the disease process. Positive RT-PCR testing confirms active WNV infection (CDC, 2023). In patients with Central Nervous System infections, CSF analysis reveals elevated protein and lymphocytes due to the inflammation caused by WNV. An MRI of the brain can show hyperintensity in the affected parts of the brain and spinal cord. However, cross-reactivity with other flaviviruses (e.g., Zika, Dengue, Yellow Fever) poses diagnostic challenges, especially in resource-limited settings where access to advanced diagnostics is limited. Expanding healthcare access and strengthening infrastructure in underserved areas is essential for timely outbreak detection.
Prevention
At the moment, there exists no licensed human vaccine for WNV, so prevention relies on personal protection, blood donor screening, and mosquito control measures (CDC, 2020). Strategies include implementing nets on windows and doors to restrict the entry of mosquitoes into living spaces, wearing long sleeves/pants, and using mosquito repellent in outdoor activities like camping to combat the transmission of WNV (Johns Hopkins Medicine, 2023). Blood donor screening for WNV antibodies is also a commonly used practice to prevent transmission through blood transfusions and organ transplantation (CDC, 2021). Along with these personal measures, many areas prone to high transmission employ community-wide interventions like larviciding and aerial spraying. However, even such community measures may not be sufficient for prevention. On a larger scale, government interventions, specifically mosquito control programs, have taken the initiative to reduce the breeding of mosquitoes by setting measures on pesticides used to kill mosquitoes and draining stagnant water to prevent breeding.
Accounting for the current state of global warming in the world, prevention has been made more difficult by facilitating more favorable environments for mosquito breeding and straining the public health infrastructure currently in use. Not only are we in need of stricter climate
regulations to protect our world, but also to minimize the spread of a multitude of viruses, with West Nile Virus listed among the many (Charles B. Beard et al., 2016). Emphasis on vector management, expanding surveillance systems, and bridging the healthcare inequities within vulnerable populations is necessary in this collective effort to limit the spread of WNV.
Treatment
There are no vaccines or medications approved for WNV, but there are many efforts that can be taken to minimize the symptoms and hospitalization for severe implications due to WNV, including pain medications, fluids, and rest, as is the case for the treatment of many other viruses. Further investment in translational research on WNV is needed, particularly considering the heightened risks of the climate crisis and the widening range of outbreaks. For comparison, the U.S. National Institutes of Health has allocated approximately $3.4 million a year to WNV, while the NIH allocated nearly $230 million a year to research for Zika Virus, a similar counterpart. Many experimental treatments for antiviral drugs and antibodies are being investigated, but the most effective solution as of now is prevention through both individual and extensive collective measures (CDC, 2022).
Conclusion
Ultimately, West Nile Virus continues to grow as a global health threat, exponentially driven by the climate crisis. Although many cases of WNV infections are mild, the existing cases of severe neuroinvasive disease and irreversible damage emphasize the need to take precautions in preventing and preparing for the transmission of WNV. Accelerated vaccine research is of utmost importance, followed by equitable healthcare access to vulnerable populations and mosquito control programs. This case of studying WNV in the context of climate change shows the extent to which the environment is connected to human health, calling for necessary public health action to mitigate these effects.
References
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