What can employers do to reduce 

the risk to workers?

Employers should keep in mind that elimination of mosquito breeding grounds is a highly effective way of reducing mosquito populations and reducing the number of mosquito bites. Mosquitoes lay eggs in standing

water. Employers with employees working in

and around areas of stagnant water should:

• Be aware of working conditions, i.e., the

presence of equipment or areas where

water accumulates.

• Advise employees to inspect work areas

and, where possible, get rid of sources of

stagnant or standing water to remove a

potential breeding ground of mosquitoes. 

• Reduce or eliminate mosquito populations

by disrupting mosquito breeding grounds

(i.e., whenever possible, drain ditches, gutters, etc., to get rid of sources of stagnant

or standing water). 

• Encourage workers to protect themselves

from skin contact with dead birds. CDC recommends using gloves or an inverted plastic bag when handling dead birds.

What can workers do to protect 

themselves?

It may not always be possible to eliminate all

potential mosquito breeding grounds.

Knowledge of some key steps that employees can take to minimize the risk of mosquito

bites is, therefore, important in reducing the

risk of WNV infection. Employees who work

What are the signs and symptoms 

of West Nile Virus?

In most cases, persons infected with WNV

either show no symptoms or have very mild

flu-like symptoms, called West Nile fever.

These mild cases of West Nile fever normally

last only a few days and are not believed to

cause any long-term effects. The typical time

from infection to the onset of signs and

symptoms is 3 to 14 days. Signs and symptoms of the milder illness, West Nile fever,

include headache, fever, body aches, swollen

lymph nodes, and/or a skin rash on the body. 

According to the Centers for Disease Control

and Prevention (CDC), severe illness is reported to occur in about 1 in every 150 persons

infected with WNV. Symptoms of severe disease may last several weeks and may have

permanent neurological effects. The signs

and symptoms of more severe infection

(West Nile encephalitis or meningitis) include

headache, high fever, stiffness in the neck,

disorientation (in very severe cases, coma),

tremors and convulsions and muscle weakness (in very severe cases, paralysis).

Persons who develop symptoms of severe

WNV illness should seek medical attention

immediately, as this disease can be fatal.

How can workers become exposed?

Flooded areas, particularly in warm climates,

provide the opportunity for mosquitoes to

breed in stagnant water. Bites from infected

mosquitoes may result in WNV.

FactSheet

West Nile Virus

West Nile Virus (WNV) infection is an illness transmitted to humans primarily by

mosquitoes. The pathogen that causes WNV infection is a virus that is known to

infect birds and other animals as well as humans. Employees working outside

are at risk, particularly in warmer weather (when mosquitoes are more likely to

be present). The following information below is designed to educate employers

and workers on the virus and also offer ways to reduce the risks of infection.
outdoors should be aware that the use of

personal protective equipment and techniques is essential to preventing mosquito

bites. Employees should:

• Cover as much of the skin as possible by

wearing shirts with long sleeves, long

pants and socks whenever possible. Use

light weight clothing to minimize the potential for heat-induced illnesses. 

• Use insect repellents containing DEET on

skin that is not covered by clothing.

According to the CDC, the most effective

repellents contain DEET (N, N-diethyl-mtoluamide or N, N-diethyl-3-methylbenzamide).

• Avoid the use of perfumes and colognes

when working outdoors during peak times

when mosquitoes may be active; mosquitoes may be more attracted to individuals

wearing perfumes and colognes.

• Choose a repellent that provides protection

for the amount of time that you will be outdoors/in areas of concern. The more DEET

a repellent contains, the longer time it can

protect one from mosquito bites, with protection times ranging from 1 hour (4.75%

DEET) to 5 hours (23.8% DEET).

• Spray insect repellent on the outside of

one’s clothing, as it is possible for mosquiThis is one in a series of informational fact sheets highlighting OSHA programs, policies or 

standards. It does not impose any new compliance requirements. For a comprehensive list of 

compliance requirements of OSHA standards or regulations, refer to Title 29 of the Code of Federal

Regulations. This information will be made available to sensory impaired individuals upon request.

The voice phone is (202) 693-1999; teletypewriter (TTY) number: (877) 889-5627.

toes to bite through thin clothing.

• Do NOT spray insect repellent on skin that

is under clothing.

• Never apply repellents over open wounds

or irritated skin. 

• Do NOT spray aerosol or pump products in

enclosed areas. Do NOT spray a pump or

aerosol product directly on one’s face. First

spray on hands and carefully rub on face

(do not allow insect repellent to contact

one’s eyes and mouth).

• After working in areas where mosquitoes

are a concern, use soap and water to wash

skin that has been treated with insect repellent. 

• Be extra vigilant at dusk and dawn when

mosquitoes are most active.

Additional Resources:

CDC West Nile Virus Home Page at:

www.cdc.gov/ncidod/dvbid/westnile/index.

htm

The U.S. EPA (information on the use of

insect repellents): www.epa.gov/pesticides/

factsheets/insectrp.htm

OSHA at www.osha.gov/dts/shib/

shib082903b.html

U.S. Department of Labor

www.osha.gov

(800) 321-OSHA

For more complete information:

DEP 9/2005