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.

New Hampshire

West Nile Virus in New Hampshire

West Nile Virus is showing early 2026 season activity across multiple states before the typical transmission season begins. Positive mosquito pools have been confirmed in Texas (San Antonio, Frisco), Louisiana (New Orleans), and six California counties. Human cases have already been confirmed in Colorado. Peak transmission season runs July through September — and an above-average season is projected for 2026. Most infections are mild or asymptomatic, but about 1 in 150 infected people develop severe, potentially fatal brain inflammation.

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¿Qué es 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.

Síntomas

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)

Transmisión

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.

Período de Contagio: Not contagious person-to-person; can be in blood of infected person during illness

Prevención

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

New Hampshire Recursos de Salud

Información del departamento de salud local y orientación de prevención específica del estado

Estamos Monitoreando New Hampshire

Nuestra vigilancia impulsada por IA monitorea continuamente la actividad de West Nile Virus en todo New Hampshire. Rastreamos datos de departamentos de salud estatales, hospitales locales, informes del CDC y más de 50 fuentes de salud globales para proporcionar advertencia temprana de amenazas emergentes.

Reciba notificaciones instantáneas cuando la actividad de West Nile Virus aumenta en New Hampshire o en su condado específico.

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New Hampshire Departamento de Salud

Para alertas oficiales de salud del estado, ubicaciones de vacunación y orientación de salud pública específica de New Hampshire, visite el sitio web del departamento de salud de su estado.

→ New Hampshire Departamento de Salud → CDC West Nile Virus Information → CDC Health Topics

Understanding West Nile Virus: Key Questions

Ya sea que viva en New Hampshire or are traveling there, knowing the symptoms, timeline, and when to seek care helps you act quickly if exposure occurs.

Cuándo Buscar Atención Médica

Seek care if you experience severe dehydration, bloody stools, high fever, or symptoms lasting more than 3 days. Children under 5, adults over 65, and immunocompromised individuals should seek care earlier.

Síntomas de emergencia: Severe dehydration, inability to keep fluids down for 12 or more hours, or neurological symptoms require emergency care.

Recursos Expertos y Referencias

Información confiable de las principales organizaciones de salud

CDC

Orientación oficial de los Centros para el Control y la Prevención de Enfermedades de EE. UU.

Ver Recursos del CDC →

WHO

Vigilancia global de enfermedades y directrices de la Organización Mundial de la Salud

Ver Recursos de la OMS →

Investigación

Últimas investigaciones revisadas por pares y estudios clínicos

Ver Investigación →

Contenido Revisado Médicamente

La información sobre enfermedades en Virus Watcher es revisada por nuestro Epidemiólogo Jefe, ex analista principal del CDC para el pronóstico FluSight. Los datos de brotes se agregan de fuentes verificadas incluyendo BEACON, ProMED, OMS, CDC y más de 50 agencias nacionales de salud. Esta información es con fines educativos y no debe reemplazar el asesoramiento médico profesional.

Última revisión: 2026-08-13

Recent West Nile Virus Reports

No confirmed cases reported in New Hampshire yet. Here are the latest West Nile Virus reports from our global surveillance network.

Greece and Italy are reporting the highest West Nile virus activity in Europe this season. The spread of West Nile virus -- a mosquito-borne disease transmitted primarily by infected mosquitoes -- in Greece is showing an upward trend, according to the National Public Health Orga…

Greece · 2026-08-12

West Nile virus is most commonly spread through mosquitoes and symptoms can range from non-existent to severe.Getty Summer isn't over yet -- and neither is mosquito season, which means you still have a very real chance of catching West Nile virus. In fact, every year, cases of t…

United States · Alaska · 2026-08-12

Holidaymakers heading to Spain have been warned to take precautions after the country's first death this year from a virus - with experts fearing the disease could spread to more hotspots. An 82-year-old man from Dos Hermanas, near Seville, has become Spain's first confirmed fat…

United States · Alaska · 2026-08-10

More than 240 cases of West Nile virus infection have been reported in Europe since the start of the season. Italy has been particularly hard hit. The WHO has called for increased vigilance. As of last Wednesday, a total of 241 cases had been reported in seven European countries…

United States · Alaska · 2026-08-08

Mosquitoes carrying deadly West Nile virus have been detected in the Spanish regions of Fuengirola and Mijas - both of which are visited by thousands of Brits each year Two popular Spanish holiday hotspots are on red alert after several people were struck down by the potentially…

Spain · 2026-07-27

The World Health Organisation has issued a warning over a fast-growing outbreak Brits heading to some of Europe's most popular sunshine hotspots this summer are being urged to take extra care, after health chiefs warned a fast-growing West Nile virus outbreak is spreading across…

World · World · 2026-07-28

California has recorded its first West Nile virus death of 2026 after a Kings County resident died from the mosquito-borne illness, health officials announced Monday. The death comes weeks after Kings County confirmed its first human case of the 2026 season, according to KGPW. …

United States · Alaska · 2026-08-04

AUSTIN (KXAN) -- A mosquito trap in Buda has tested positive for West Nile virus, according to the Hays County Development Services Mosquito Surveillance Program. The positive sample was collected in the 78610 ZIP code and marks the fifth West Nile virus-positive mosquito pool i…

United States · Alaska · 2026-08-05

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Preguntas Frecuentes

Preguntas frecuentes sobre West Nile Virus respondidas por nuestro equipo de epidemiología

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Obtenga West Nile Virus Alertas para New Hampshire

Reciba notificaciones instantáneas cuando la actividad de West Nile Virus aumenta en New Hampshire o sus destinos de viaje. Rastree más de 200 enfermedades con alertas basadas en ubicación. Utilizado por sistemas de salud, servicios de emergencias médicas, escuelas y viajeros de todo el mundo.