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1. Where did West Nile virus come from?

West Nile virus is commonly found in humans and birds and other vertebrates in Africa, Eastern Europe, West Asia, and the Middle East. West Nile virus was first isolated in the West Nile province of Uganda in 1937 (3, 4). The first recorded large epidemics occurred in Israel from 1951 to 1954, and the largest recorded epidemic to date occurred in South Africa during 1974. Large human outbreaks of WN Encephalitis occurred in Israel in 2000 and have occurred in Southern France (1962), in southeastern Romania (1996), and in south-central Russia (1999) (5,6). Until 1999, West Nile encephalitis had not been documented in the Western Hemisphere. It is not known where the U.S. West Nile virus originated, but it is most closely related genetically to strains found in the Middle East.

2. How long has West Nile virus been in the U.S.?

It is not known how long it has been in the U.S., but Center for Disease Control and prevention (CDC) scientists believe the virus has probably been in the eastern U.S. since the early summer of 1999, possibly longer.

3. I understand West Nile virus was found in "overwintering" mosquitoes. What does this mean?

One of the species of mosquitoes found to carry West Nile virus is the Culex species, which can survive through the winter, or "overwinter," in the adult stage. An infected mosquito can likely harbor the virus during the winter months and can transmit the virus in the following year.

4. How do people get West Nile encephalitis?

People become infected by the bite of a mosquitoes infected with West Nile virus.

5. If I live in an area where birds or mosquitoes with West Nile virus have been reported and a mosquito bites me, am I likely to get sick?

No. Even in areas where mosquitoes do carry the virus, very few mosquitoes are likely infected. Only a small percentage of people who become infected will get severely ill. The Maine Environmental Policy Institute (MEPI) estimates that in areas where West Nile Virus is endemic, approximately one in 1,000 mosquitoes actually carry the virus. The MEPI also estimates that only one in 300 people bitten by a West Nile Virus infected mosquito will show any signs of sickness. Even if you contract the WNV and become ill, most people will only exhibit mild flu-like symptoms. The chances you will become severely ill from any one mosquito bite are therefore small.

6. How does West Nile virus actually cause severe illness and death in humans?

Following transmission by an infected mosquito, West Nile virus multiplies in the person's blood system and crosses the blood-brain barrier to reach the brain. The virus interferes with normal central nervous system functioning and causes inflammation of brain tissue.

7. What proportion of people with severe illness due to West Nile virus die?

Among those that have the neuro-invasive form of the disease, case-fatality rates range from three to 15% and are highest among the elderly.

8. Is there a vaccine against West Nile encephalitis?

Not currently.

9. Is adulticide an effective means of controlling mosquitos?

Adulticiding, or the killing of adult mosquitoes by ground or aerial applications of chemicals, is considered by the Center for Disease Control and Prevention to be the least efficient mosquito control method. There are several reasons adulticiding is not highly effective. For example, mosquito species have different preferences for flight times and habitats, which makes timing spray events difficult. In areas where there are many houses, trees, and other obstructions, the chance of actually hitting a mosquito with the spray cloud is greatly diminished. Although it is very difficult to measure the efficacy of a large spray event, the results of trap experiments conducted in Houston and Florida suggest that a large spray event will typically reduce the adult population of mosquitoes by only about 30%.

10. ¿Se puede tratar el virus del Nilo occidental?

No existe un tratamiento específico para la infección por VNO. En casos más leves, las personas experimentan síntomas como fiebre y dolores que pasan eventualmente; aunque, la enfermedad puede durar semanas o meses. En casos graves, una persona puede ser hospitalizada y recibir tratamiento de apoyo (por ejemplo, líquidos intravenosos (sueros), ayuda con la respiración), junto con la atención de enfermería. Actualmente no hay vacuna para el VNO, pero el CDC está trabajando con socios para desarrollar una.

11. ¿Cuál es el riesgo de enfermarse del Virus del Nilo Occidental?

Personas mayores de 50 años corren mayor riesgo de contraer una enfermedad grave; aunque, a cualquier edad podría enfermar gravemente. Estar afuera sin tomar precauciones significa que usted está en riesgo; cuanto más tiempo pase al aire libre (trabajando o jugando) más tiempo usted está expuesto a las picaduras de un mosquito infectado. El riesgo de transmisión del virus a través de procedimientos médicos es muy bajo. El embarazo y la lactancia NO aumentan el riesgo de infectarse con el VNO.

12. ¿Pueden infectarse los animales con el virus del Nilo Occidental?

Sí. El VNO puede infectar a casi cualquier animal, incluyendo perros y gatos - sin embargo, la buena noticia es que rara vez, si es que alguna vez, se enferman por el virus. Los caballos parecen ser el único animal doméstico afectado negativamente por el VNO, y hay una vacuna disponible.

13. ¿Todos los mosquitos portan el Virus del Nilo Occidental?

Number En esta área, es transmitida principalmente por miembros de la especie Culex, y sólo los mosquitos hembras pican a los seres humanos. Normalmente, este mosquito vuela distancias cortas (a menudo mucho menos de una milla) para alimentarse. Los mosquitos adultos tienen una vida de unas pocas semanas durante los meses de verano.