West Nile Virus Fact Sheet

(Program on Communicable Diseases, 13 September 2000)

Old World
First discovery	Western Nile, Uganda, Africa, 1937
Other endemic areas	Uganda Central African Republic Madagascar South Africa Egypt	France Rumania Israel Italy Russia India
New World
First Discovery	New York, 1999	1999, 62 cases in 4 states 2000, 21 cases in 5 states 2001, 66 cases in 11 states 2002, 673 cases in 41 states*
Virus isolation in other countries	Cayman Islands (2001), Canada (2002)
CFR* in clinical cases *CFR = Case Fatality Rate	(1999) 7 in 62 = 11.29% (2000) 2 in 21 = 9.52% (2001) 9 in 64 = 14.06% (2002) 32 in 673 = 4.75%*	In US outbreaks, about 1 infected person in 150 has become seriously ill with central nervous system infection (encephalitis and/or meningitis).
FLU-like symptoms have been reported by about 30% of infected people, but most of those infected do not get sick.
Reservoirs
Birds (virus amplifiers)	English sparrows Crows (Corvidae) Pigeons	Birds are far more likely than people to become infected and sickened by West Nile Virus.
Birds are the most probable route of dissemination of the disease to other countries in the Region.
Mammals (dead end hosts)	Horses Humans Pets (dogs, cats, rabbits, etc.) Other animals	The United States the USDA-APHIS has granted a provisional license for the use of a vaccine composed of killed virus for horses.
Vectors
Mosquitoes	Culex pipiens Culex tarsalis Culex quinquefasciatus Other Culex spp. Other Aedes spp. Other Ochlerotatus spp.	Most mosquito bites will not lead to a WNV infection.
As a health risk to humans
Symptoms of serious illness	Fever, disorientation, muscle weakness, neck stiffness, headache, nausea
Risk of serious illness	Greater for older people and the immuno-compromised.
Children are not particularly vulnerable.	Few if any cases of serious illness have involved children.
Incubation period	3-14 days after being bitten by an infected mosquito.
What to do	Persons who develop symptoms of serious illness should seek attention from a health-care professional immediately.
Treatment	Treat the symptoms. There is no vaccine or medication specific to WNV.
Transfusion (transplantation)	Recent evidence suggests that there may be transmission via transfusion or organ transplantation.
Prevention & Control
The most effective way to prevent transmission of WNV is to reduce exposure to the vector.
A critical component of any WNV control program is public education about the disease, how it is transmitted, and how to prevent or reduce the risk of exposure. Public education efforts should make use of behavioral science and social marketing methods to communicate the information effectively to the target populations.
Individuals can take certain precautions to reduce their exposure to the virus in the home, by the following:	Put screens on windows and block any holes in the house where mosquitoes can enter. Wear long pants and long-sleeved shirts, particularly when remaining outdoors for extended periods, especially at times when mosquitoes are active. Minimize outdoor activities at dawn and dusk, when mosquitoes are most likely to bite. Use insect repellents with up to 35% of the active ingredient DEET for adults and up to 20% for children.
The most effective way of controlling mosquitoes is by larval source reduction. This is best done through programs that reduce breeding sites, monitor mosquito populations, and initiate control measures before the disease is transmitted. Such programs can also be used as the first-line emergency response in the event that viral activity is detected or the disease is reported in humans. Larvicides are useful in breeding sites that cannot be eliminated, but the control of adult mosquito populations through aerial spraying of insecticides is usually a last resort.
* To 4 September 2002.

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Guidelines for the Prevention and Control of West Nile Virus

Related Sites: West Nile Virus

	The Pan American Health Organization Promoting Health in the Americas