West Nile Virus: An Expanding Threat

By Ana Espino | Published on June 25, 2026 | 4 min read

West Nile virus (WNV) is an arbovirus transmitted primarily by mosquitoes of the Culex genus. First identified in Uganda in 1937, it is now present across multiple continents and has become one of the leading causes of mosquito-borne viral encephalitis. Once considered a sporadic infection, WNV has evolved over recent decades into a growing public health threat in Europe, North America, and parts of Asia and the Middle East.

In a recent review examining the epidemiology, surveillance, and prevention strategies related to West Nile virus, the authors analyze the mechanisms driving its global spread, as well as recent advances in understanding its biology and control. Their synthesis highlights, in particular, the increasing influence of climate change on the virus’s transmission dynamics.


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A Transmission Cycle Facilitated by Environmental Changes

The virus naturally circulates between wild birds, which serve as its primary reservoir, and Culex mosquitoes, the main vectors responsible for transmission. Humans and horses are considered incidental or “dead-end” hosts, as they generally do not develop sufficient levels of virus in their bloodstream to sustain further transmission.

Authors emphasize that rising temperatures, changing precipitation patterns, and the geographic expansion of mosquito populations are increasingly facilitating viral circulation in regions that were previously only minimally affected. Several recent studies have demonstrated a correlation between favorable climatic conditions and the emergence of epidemic outbreaks in Europe.


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An Infection That Is Often Silent but Sometimes Severe

Most human infections remain asymptomatic. However, approximately 20% of infected individuals develop a febrile illness characterized by fatigue, headache, muscle pain, and skin rash.

In fewer than 1% of cases, the infection progresses to a severe neuroinvasive disease, leading to encephalitis, meningitis, or acute flaccid paralysis.

These complications occur particularly among older adults and immunocompromised individuals. Some neurological sequelae may persist long after the acute phase of infection, highlighting the importance of early diagnosis and careful clinical monitoring.


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A Concerning Increase in Europe

The review highlights the recent rise in human cases across several European countries. Italy has emerged as one of the main hotspots of viral circulation on the continent. Recent studies have documented the rapid spread of new viral lineages associated with an increased risk of neuroinvasive disease during outbreaks observed in recent years.

Authors also stress that integrated surveillance of human, animal, and entomological populations is becoming essential for the early detection of viral circulation and the anticipation of epidemic outbreaks.


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Promising Vaccines but Limited Availability for Humans

Although several vaccines are already used successfully in horses, no widely available vaccine currently exists for the general human population. Research is ongoing using a variety of vaccine platforms, including inactivated vaccines, recombinant vaccines, and viral vector-based vaccines. Several recent candidates have demonstrated encouraging results in preclinical studies.

At the same time, multiple therapeutic strategies targeting viral proteins involved in replication are under development, although no specific antiviral treatment has yet demonstrated sufficient clinical efficacy.

A “One Health” Approach Has Become Essential

Given the expanding geographic range of West Nile virus, the authors conclude that controlling this arboviral disease requires an integrated One Health approach combining human, veterinary, and environmental surveillance.

Strengthening mosquito and bird monitoring programs, improving early warning systems, and accelerating the development of human vaccines are considered major priorities for reducing the future impact of this emerging disease.

In a context marked by climate change and increasing interactions between humans, animals, and disease vectors, West Nile virus is now regarded as one of the most emblematic examples of the public health challenges posed by emerging vector-borne diseases.


About the author – Ana Espino
PhD in Immunology, specialized in Virology  
As a scientific writer, Ana is passionate about bridging the gap between research and real-world impact. With expertise in immunology, virology, oncology, and clinical studies, she makes complex science clear and accessible. Her mission: to accelerate knowledge sharing and empower evidence-based decisions.