How serious is West Nile Virus?

About 80% have no symptoms. 20% develop West Nile fever (flu-like illness). About 1 in 150 infected people develop severe neurological disease (encephalitis/meningitis) which is fatal in 10% of cases. Survivors of severe disease often have permanent neurological damage including muscle weakness, memory problems, and fatigue that can last months to years.

What are symptoms of severe West Nile infection?

Severe symptoms include high fever, severe headache, stiff neck, disorientation/confusion, vision loss, tremors, seizures, muscle weakness, paralysis (especially acute flaccid paralysis resembling polio), or coma. These require immediate medical attention. Symptoms typically appear 3-14 days after bite from infected mosquito.

Who is at highest risk for severe West Nile?

People over 60 are at greatest risk for severe disease. Other high-risk groups: those with cancer, diabetes, hypertension, kidney disease, organ transplant recipients, and immunocompromised individuals. Pregnancy doesn't increase severity risk, but infection can rarely transmit to fetus.

Is there a vaccine or treatment for West Nile?

No vaccine or specific antiviral treatment exists for humans (equine vaccine available for horses). Treatment is supportive care: hospitalization for severe cases, IV fluids, respiratory support, prevention of secondary infections. This makes mosquito bite prevention the only defense. Early recognition and supportive care improve outcomes.

When and where is West Nile most common?

In the U.S., peak season is July through September when mosquitoes are most active. All 48 contiguous states have reported cases, but highest activity occurs in warm, dry climates with stagnant water (California, Texas, Arizona, Louisiana). Climate change is expanding mosquito seasons and geographic range.

Can you get West Nile more than once?

Rare but possible. After infection, most people develop lifelong immunity. However, immunocompromised individuals may not develop full immunity. There are no documented cases of reinfection in immunocompetent people, but researchers continue to study long-term immunity duration.

West Nile Virus

10 Active Outbreaks

West Nile Virus is a mosquito-borne disease that can cause serious neurological illness. Most infections are mild or asymptomatic, but about 1 in 150 infected people develop severe, potentially fatal brain inflammation.

Countries Affected

919

Recent Cases (30d)

Active Outbreaks

18d ago

Last Updated

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What is West Nile Virus?

West Nile Virus arrived in the U.S. in 1999 and has since become the leading mosquito-borne disease in the country. It's transmitted by Culex mosquitoes that bite infected birds. While 80% of infected people have no symptoms, severe cases can cause encephalitis or meningitis with long-term neurological effects. Age over 60 significantly increases risk of severe disease.

Symptoms

Mild (West Nile fever): Fever, headache, body aches, joint pain, vomiting, diarrhea, rash
Severe: High fever, severe headache, stiff neck, disorientation, tremors, seizures
Neurological: Muscle weakness, vision loss, paralysis, coma
Long-term effects: Fatigue, memory problems, muscle weakness (can persist months/years)

Transmission

Transmitted through bites of infected Culex mosquitoes. Rarely through blood transfusion, organ transplant, mother to fetus, or breastfeeding. NOT spread person-to-person through casual contact.

Contagious Period: Not contagious person-to-person; can be in blood of infected person during illness

Prevention

Use EPA-registered insect repellents (DEET, picaridin, IR3535, oil of lemon eucalyptus)
Wear long sleeves and pants at dawn/dusk when mosquitoes most active
Install/repair window and door screens
Use air conditioning when possible
Eliminate standing water (buckets, flower pots, bird baths, gutters)
Change water in pet bowls, birdbaths weekly
Treat or drain swimming pools, fountains
Community mosquito control programs (spraying, larvicides)
Avoid outdoor activities at dawn/dusk during peak season

Active Outbreaks & Recent Cases

Real-time intelligence from global health monitoring and AI-powered surveillance

Data sources: BEACON, ProMED, WHO, CDC, and 50+ national health agencies

✓ Live data updated in real-time from global health sources

West Nile Virus Hits Anguilla First Local Case

Anguilla 2026-03-13

Active

Anguilla confirmed its first autochthonous (locally acquired) human case of West Nile virus in March 2026, while evidence of viral circulation in birds, horses, and mosquitoes has existed across Caribbean territories since the early 2000s.

Source: BEACON - View Full Report

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🚨 Researchers say xAI has minimal air quality impact; Shelby County reports 9 West Nile cases

United States, Alaska 2025-10-01

Active

Shelby County has reported nine cases of West Nile virus, indicating an active, localized outbreak. Residents in the affected area need to take immediate preventative measures against mosquito bites.

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West Nile Virus Arrives Early in Italy

Italy 2026-05-18

Active

A single laboratory-confirmed West Nile virus case has been identified in Oristano, Sardinia, in mid-May 2026 — earlier in the season than historically typical — in an elderly individual who has since recovered. While the current situation is limited to one confirmed case with no fatalities or evidence of wider spread, the early detection is notable given Italy's sustained and geographically expanding WNV endemicity.

Source: BEACON - View Full Report

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🚨 State health officials confirm two more West Nile virus infections - The Boston Globe

United States, Alaska 2025-09-28

Active

State health officials have confirmed two additional West Nile virus infections. This indicates an active spread of the mosquito-borne disease, which can cause severe neurological illness.

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🚨 Arizona mom warns of mosquito dangers after son contracts West Nile

United States, Alaska 2025-10-01

Active

An Arizona mother is warning the public about mosquito dangers after her son contracted West Nile Virus. This highlights an active and ongoing public health threat requiring immediate preventative action from residents in the affected area.

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West Nile virus, India

India 2026-04-28

Active

This event envelope contains reports on WNV cases, clusters and outbreaks in India.

Source: BEACON - View Full Report

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West Nile Virus Neuroinvasive Case Hits Texas, Early Season

United States 2026-05-21

Active

This envelope collects reports on West Nile virus (WNV) disease in the US.

Source: BEACON - View Full Report

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Man issues warning after contracting dangerous disease while doing yard work: 'Make sure that people are aware'

World, World 2025-11-08

Active

In Canada's warmer-than-usual summer in 2025, some homeowners stayed busy with outdoor tasks. However, this also provided mosquitoes with an extended period to prey on unsuspecting humans. Ontario resident René van den Berg spent 11 days in the hospital after contracting the West Nile virus (WNV) i... Source: Yahoo - Read Full Article

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'Avoid mosquito bites': 9th human case of West Nile virus identified this season, health officials say - The Boston Globe

World, World 2025-10-25

Active

"This case is a reminder that WNV infections can occur even in the fall, and we should remain vigilant," said Public Health Commissioner Robbie Goldstein in a statement. "We are now past the peak season for West Nile virus in Massachusetts, but some risk will continue until the first hard frost." W... Source: The Boston Globe - Read Full Article

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Denton County reports third human case of West Nile virus this year, officials say

World, World 2025-11-06

Active

The Denton County Public Health department on Thursday reported the third human case of West Nile virus in the county, according to a news release. The person who contracted West Nile virus lives in Denton, but the county declined to release any information about the patient. To respect patient co... Source: The Dallas Morning News - Read Full Article

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Expert Resources & References

Trusted information from leading health organizations

CDC

Official guidance from the U.S. Centers for Disease Control and Prevention

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WHO

Global disease surveillance and guidelines from the World Health Organization

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Research

Latest peer-reviewed research and clinical studies

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Medically Reviewed Content

Disease information on Virus Watcher is reviewed by our Chief Epidemiologist, a former CDC lead analyst for FluSight forecasting. Outbreak data is aggregated from verified sources including BEACON, ProMED, WHO, CDC, and 50+ national health agencies. This information is for educational purposes and should not replace professional medical advice.

Last reviewed: 2026-06-08