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The Florida Department of Health works to protect, promote & improve the health of all people in Florida through integrated state, county, & community efforts.

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Dr. Carina Blackmore
State Public Health Veterinarian,
Deputy State Epidemiologist

Dr. German Gonzalez
Director Médico Ejecutivo,
Bureau de Epidemiologia

Disclaimer: These video's are free for the use of the public and media.

West Nile Virus (WNV)

Contact the Florida Department of Health

West Nile virus (WNV) is a mosquito-borne flavivirus that causes mild to severe illness. It was first identified in Uganda in 1937. WNV was first introduced to the United States in 1999 in New York and reached Florida in 2001.  Since its initial detection, human cases of WNV have been reported in all U.S. states with the exception of Alaska and Hawaii. The virus is now considered endemic in the U.S., with annual epidemics in some parts of the country, peaking in the late summer months.

  • Frequently Asked Questions

Most West Nile virus infections (approximately 80%) are asymptomatic.  In those people that do develop symptoms, most experience a mild illness termed West Nile Fever (WNF) that is characterized by headache, fever, pain, and fatigue.  Less than 1% of infected people develop the most severe form of disease, neuroinvasive WNV, which may involve meningitis and encephalitis and can cause irreversible neurological damage, paralysis, coma or death.   Symptoms typically appear between 2 and 14 days after the bite of an infected mosquito.  People over the age of 50 and individuals with weakened immune systems (especially transplant recipients and HIV infected individuals) seem to be at increased risk for severe disease.

There is no specific treatment for WNV, and most mild infections are typically overcome with little or no medical intervention within a matter of weeks. An effective vaccine has been developed for horses, however research for a human vaccine continues.

The peak period of transmission in Florida is July through September. Since its introduction, WNV activity has been identified in all 67 of Florida's counties. After the 2003 peak, the number of human cases gradually decreased over the years from 2004 to 2009 until it started showing an increase in the number of cases in 2010. Dry environmental conditions and herd immunity in bird populations may have contributed to the low number of cases during 2006-2009.

The natural cycle of WNV involves several species of Culex mosquitoes and wild birds. It can cause high rates of mortality in certain families of birds, especially crows and jays.  Occasionally, an infected mosquito will bite a human or animal (particularly horses) and cause disease. The virus can also be transmitted to humans via contaminated blood transfusions and a few cases have also been reported involving intrauterine transmission.  Since 2003, all blood donations are screened for the presence of WNV prior to transfusion.

Florida Acquired Human Cases of WNV Illness, 2001-2012 Graph

Enlarge graph of Florida Aquired Human Cases of WNV, 2001-2012

2012 represents the second highest year of record for WNV illness in Florida focused in Duval County and the Panhandle. 2012 also saw a national outbreak of WNV illness with the highest number of cases reported since the 2003 peak. The state of Texas reported 33 percent of all WNV illness cases with all lower 48 states reporting activity. The 2012 outbreak likely resulted from many factors, including higher-than-normal temperatures that influenced mosquito and bird abundance, viral replication in host mosquitoes, and interactions of birds and mosquitoes.

What Is West Nile Virus?

West Nile virus (WNV) is a potentially serious illness. Experts believe WNV is established as a seasonal epidemic in North America that flares up in the summer and continues into the fall. This fact sheet contains important information that can help you recognize and prevent West Nile virus.

What Can I Do to Prevent WNV?

The easiest and best way to avoid WNV is to prevent mosquito bites. The best preventive measure for residents living in areas infested with mosquitoes is to eliminate the places where the mosquito lays her eggs, primarily artificial containers that hold water.

To prevent mosquitoes from living and multiplying around your home or business:

DRAIN standing water:

  • Drain water from garbage cans, buckets, pool covers, coolers, toys, flowerpots or any other containers where sprinkler or rainwater has collected.
  • Discarded old tires, drums, bottles, cans, pots and pans, broken appliances and other items that aren't being used.
  • Empty and clean birdbaths and pet's water bowls at least once or twice a week.
  • Protect boats and vehicles from rain with tarps that don’t accumulate water.
  • Maintain swimming pools in good condition and appropriately chlorinated. Empty plastic swimming pools when not in use.

COVER your skin with:

  • CLOTHING - If you must be outside when mosquitoes are active, cover up. Wear shoes, socks, long pants and long sleeves.
  • REPELLENT - Apply mosquito repellent to bare skin and clothing. Always use repellents according to the label. Repellents with 10-30 percent DEET, picaridin, oil of lemon eucalyptus and IR3535 are effective.
  • Use mosquito netting to protect children younger than 2 months old.

COVER doors and windows with screens:

  • Keep mosquitoes out of your house. Repair broken screening on windows, doors, porches, and patios.

What Are the Symptoms of WNV?

  • Serious Symptoms in a Few People. About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent.
  • Milder Symptoms in Some People. Up to 20 percent of the people who become infected have symptoms such as fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks.
  • No Symptoms in Most People. Approximately 80 percent of people who are infected with WNV will not show any symptoms at all.

How Does West Nile Virus Spread?

  • Most often, WNV is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite.
  • WNV is not spread through casual contact such as touching or kissing a person with the virus.

How Soon Do Infected People Get Sick?

  • People typically develop symptoms between 2 and 14 days after they are bitten by the infected mosquito.

How Is WNV Infection Treated?

  • There is no specific treatment for WNV infection.
  • In cases with milder symptoms, people experience symptoms such as fever and aches that pass on their own, although even healthy people have become sick for several weeks.
  • In more severe cases, people usually need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing and nursing care.

What Should I Do if I Think I Have WNV?

  • Milder WNV illness improves on its own, and people do not necessarily need to seek medical attention for this infection though they may choose to do so.
  • If you develop symptoms of severe WNV illness, seek medical attention immediately.
  • Severe WNV illness usually requires hospitalization. Pregnant women and nursing mothers are encouraged to talk to their doctor if they develop symptoms that could be WNV.

What Is the Risk of Getting Sick from WNV?

  • People over the age of 50 are more likely to develop serious symptoms of WNV if they do get sick and should take special care to avoid mosquito bites.
  • Being outside means you're at risk. The more time you're outdoors, the more time you could be bitten by an infected mosquito. Pay attention to avoiding mosquito bites if you spend a lot of time outside, either working or playing.

¿Qué es el virus del Nilo occidental?

El virus del Nilo occidental (“WNV,” por sus siglas en inglés) es una enfermedad potencialmente grave. Los expertos creen que WNV está establecida como una epidemia estacional en Norte América que recrudece en el verano y continúa hasta el otoño. Esta hoja informativa contiene información importante que le puede ayudar a reconocer y prevenir el virus del Nilo occidental.

¿Qué puedo hacer para prevenir el WNV?

La mejor manera y la más fácil de evitar el WNV es prevenir las picaduras de mosquitos. La mejor medida preventiva para los residentes de áreas infestadas de mosquitos es eliminar los lugares donde el mosquito deposita sus huevos, principalmente en recipientes artificiales que contienen agua.

Para evitar que los mosquitos vivan y se multipliquen cerca de su hogar y negocio:

DRENE el agua estancada:

  • Drene el agua de los basureros, baldes, cubiertas para piscinas, neveras portátiles, juguetes, macetas o cualquier otro recipiente donde se acumula agua de lluvia o de riego.
  • Llantas viejas desechadas, barriles, botellas, latas, ollas y sartenes, electrodomésticos rotos y otros objetos que no se están utilizando.
  • Vacíe y limpie las bañeras para aves y los tazones de agua para mascotas por lo menos una o dos veces por semana.
  • Proteja de la lluvia los botes y vehículos con lonas que no acumulan agua.
  • Mantenga las piscinas en buenas condiciones y adecuadamente cloradas. Vacíe las piscinas plásticas cuando no las use.

CUBRA su piel con:

  • ROPA: si debe estar afuera cuando los mosquitos están activos, cúbrase. Use zapatos, calcetines, pantalones largos y manga larga.
  • REPELENTE: aplique repelente de mosquitos sobre la piel y la ropa. Siempre utilice los repelentes de acuerdo con la etiqueta. Los repelentes con 10 a 30% de DEET, picaridin, aceite de eucalipto limón e IR3535 son eficaces.
  • Use mosquiteros para proteger a los niños menores de 2 meses de edad.

CUBRA las puertas y ventanas con tela metálica:

  • Mantenga los mosquitos fuera de su casa. Repare la tela metálica rota en ventanas, puertas, porches y patios.

¿Cuáles son los síntomas de WNV?

  • Síntomas graves en pocas personas. Aproximadamente una de 150 personas infectadas con WNV va a desarrollar una enfermedad grave. Los síntomas graves pueden incluir fiebre alta, dolor de cabeza, cuello rígido, letargo, desorientación, coma, estremecimientos, convulsiones, debilidad muscular, pérdida de la visión, entumecimiento y parálisis. Estos síntomas pueden durar varias semanas y los efectos neurológicos pueden ser permanentes.
  • Síntomas más leves en algunas personas. Hasta el 20 por ciento de las personas que se infectan tienen síntomas como fiebre, dolor de cabeza, dolor de cuerpo, náuseas, vómitos y algunas veces glándulas linfáticas inflamadas o sarpullido en el pecho, estómago y espalda. Los síntomas pueden durar tan poco como unos días, aunque incluso las personas sanas se pueden enfermar durante varias semanas.
  • La mayoría de las personas no presenta síntomas. Aproximadamente el 80 por ciento de las personas (4 de cada 5) que se infectan con WNV no presenta ningún síntoma.

¿Cómo se propaga el virus del Nilo occidental?

  • Con más frecuencia, el WNV se propaga por el piquete de un mosquito infectado. Los mosquitos se infectan cuando se alimentan de aves infectadas. Los mosquitos entonces pueden propagar el WNV a los humanos y otros animales cuando los pican.
  • El VWN no se propaga a través del contacto casual como tocar o besar a una persona que tiene el virus.

¿Qué tan rápido se enferman las personas infectadas?

  • Por lo general, las personas desarrollan síntomas entre 2 a 14 días después de la picadura del mosquito infectado.

¿Cómo se trata la infección del WNV?

  • No hay un tratamiento específico para la infección por WNV.
  • En casos con síntomas más leves, las personas experimentan síntomas como fiebre y dolores que pasan por sí solos, aunque incluso las personas sanas se pueden enfermar durante varias semanas.
  • En los casos más graves, las personas usualmente tienen que ir al hospital donde pueden recibir tratamiento de apoyo, incluyendo líquidos intravenosos, ayuda para respirar y atención de enfermería.

¿Qué debo hacer si creo que tengo WNV?

  • La enfermedad WNV más leve mejora por sí sola y las personas no necesariamente tienen que buscar atención médica para esta infección, aunque pueden elegir hacerlo. Si desarrolla síntomas de la enfermedad WNV grave, como dolores fuertes inusuales o confusión, busque atención médica de inmediato.
  • La enfermedad grave WNV usualmente requiere hospitalización. Se recomienda a las mujeres embarazadas y madres lactantes que hablen con su médico si desarrollan síntomas que pueden ser WNV.

¿Cuál es el riesgo de enfermarse de WNV?

  • Es más probable que personas mayores de 50 años de edad desarrollen síntomas graves de WNV si se enferman y deben tener especial cuidado de evitar las picaduras de mosquitos.
  • Salir al exterior significa que usted está en riesgo. Mientras más tiempo pase al aire libre, más tiempo se expone a la picadura de un mosquito infectado. Preste atención para evitar las picaduras de mosquito si pasa mucho tiempo afuera, ya sea trabajando o jugando.