WEST NILE VIRUS
Questions and Answers
WNV was first reported in the United States in the summer of 1999. In 1999, nearly all cases of the disease in humans and animals were detected within a 75-mile radius of New York City. By 2004 the virus was reported throughout the continental United States.
For updated geographic and case information, visit the CDC West Nile Virus Home Page.
Anyone who lives or works in an area where there are WNV-infected mosquitoes is at risk of WNV infection. People of all ages are at risk of the flu-like symptoms of this infection. Although people usually recover, the symptoms may be severe enough to result in lost workdays for extended periods.
People above age 50 and those who have had organ transplants are known to have the highest risk of severe illness from WNV infection. However, people of all ages and conditions can become severely ill. Therefore, all workers should be careful to reduce their potential for exposure to WNV.
An infection with WNV is most often spread to humans from the bite of an infected mosquito. Workers at risk of WNV exposure include those working outdoors when mosquitoes are biting. Outdoor workers at risk include:
- groundskeepers and gardeners
- construction workers
- laborers, mechanics
- entomologists and other field workers
- other outdoor workers
Although WNV is most often transmitted by the bite of infected mosquitoes, the virus can also be transmitted through contact with infected animals, their blood, or other tissues. Thus laboratory, field, and clinical workers who handle tissues or fluids infected with WNV or who perform necropsies are at risk of WNV exposure. These workers include:
- laboratory diagnosticians and technicians
- veterinarians and their staff
- wildlife rehabilitators
- wildlife biologists
- zoo and aviary curators
- health care workers
- emergency response and public safety personnel
- public health workers
- others in related occupations
The West Nile virus (WNV) is most often spread to humans from the bite of an infected mosquito. Outdoor workers are at risk of WNV exposure whenever mosquitoes are biting. The virus can also be transmitted through contact with infected animals, their blood, or other tissues. Thus laboratory, field, and clinical workers who handle tissues or fluids infected with WNV or who perform necropsies are at risk of WNV exposure.
Mosquitoes may develop in any puddle or water that stands for more than four days. Workers at sites near stagnant pools, ponds, watering troughs, irrigation ditches, rain barrels, manure lagoons, or any other stagnant bodies of water are at risk of mosquito exposure. Equipment such as tires, tarps, buckets, barrels, and wheel barrows may allow mosquito larvae to develop if water accumulates in them. Even water-filled ruts on the ground attract mosquitoes.
Work sites with standing water allow mosquitoes to breed.
Many mosquitoes bite people most actively from dusk to dawn. When possible, avoid working outdoors when mosquitoes are biting. Some mosquitoes are active during the day—particularly in weedy, bushy, and wooded or shaded areas. When possible, avoid working in these habitats. See below for recommendations about using personal protection when such habitats cannot be avoided.
Avoid handling dead animals when possible. Avoid direct contact with them by using tools such as shovels. If you must handle them, wear medical examination gloves that provide a protective barrier between your skin and blood or other body fluids. Make sure that any latex gloves used are reduced-protein, powder-free gloves to reduce workers’ exposure to allergy-causing proteins. When heavy work gloves are needed, they may be worn as the outer pair with medical examination gloves as the inner pair. Cotton, leather, and other absorbent gloves are not protective when worn alone. If gloves are not available, use a plastic bag, which may act as a protective barrier between the animal and your skin.
Most human infections with WNV (about 80%) cause no symptoms, and about 20% cause flu-like symptoms, including fever, fatigue, headache, and muscle or joint pain. Fewer than 1% of humans infected with WNV become severely ill. Severe symptoms include high fever, stiff neck, disorientation, tremors, muscle weakness, and paralysis. Severely affected persons may develop encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes of the brain or spinal cord). Severe cases may be fatal. People of all ages and conditions may be affected. However, those who are above age 50 or who have had an organ transplant are at increased risk of severe illness.
The Centers for Disease Control and Prevention (CDC) has followed a number of women who became ill with WNV during pregnancy. Most of these women delivered apparently healthy babies with no evidence of WNV infection. Although some of the babies born to WNV-infected mothers did have health problems, it is unknown whether the WNV infection caused these problems. Because of the limited number of cases studied so far, it is not yet possible to determine what percentage of WNV infections during pregnancy result in infection of the fetus or medical problems in newborns. More research is needed to understand the possible effects of WNV on pregnancy.
When pregnant workers are outside, they should follow recommendations to reduce their risk for WNV infection. These recommendations include avoiding mosquitoes; wearing protective clothing; using repellents containing DEET (N,N-diethyl-m-toluamide), picaridin, or oil of lemon eucalyptus on the skin; and spraying clothes with one of these repellents or permethrin. Always follow label instructions for repellents. Pregnant women who become ill should see their health care providers.
Any worker who has health concerns should contact his or her health care provider. Testing for WNV infection is available. No specific treatment exists for WNV infection. Treatment consists of supportive care for the individual. Currently, no approved vaccine exists to prevent WNV infection in humans.
- National Institute for Occupational Safety and Health (NIOSH)
- Centers for Disease Control and Prevention
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