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NIOSH Safety and Health Topic:

West Nile Virus

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Overview

West Nile Virus

mosquito biting finger

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Overview
 
Questions and Answers
 
Recommendations for Outdoor Workers
 
Recommendations for Lab Workers
 
References
 

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WNV Infection in Humans
 
History of WNV in the U.S.
 
Occupational Risks of WNV
 

 

The West Nile virus (WNV) is transmitted by mosquitoes to birds and other animals through a mosquito bite. The WNV normally cycles between mosquitoes and birds. However, people may also be infected if they are bitten by a WNV-infected mosquito. Most cases of WNV are probably not acquired in the workplace but there are some workers at risk of WNV infection. Outdoor workers are at risk of WNV infection from the bite of an infected mosquito. Workers who perform necropsies of infected birds or handle WNV-infected tissues or fluids are also at risk of WNV infection if skin penetration or laceration occurs.

WNV Infection in Humans

The most likely route of WNV infection to humans is through the bite of an infected mosquito. WNV may also be transmitted by organ transplantation, blood transfusion, or possibly breast milk [CDC 2002a,b]. Transplacental (mother-to-fetus) infection has occurred [CDC 2002c]. Laboratory-acquired infection has also been documented [CDC 2002d]. Turkey breeder farm workers have been infected with WNV [CDC 2003]. The mode of transmission to these farm workers is uncertain.

Most human WNV infections cause either no symptoms or a mild flu-like illness. The most severely affected patients may develop an inflammation of the brain, or the membranes of the brain or spinal cord, or both, called encephalitis, meningitis, or meningoencephalitis, respectively. These severe cases may be fatal. Persons over age 50 are at higher risk of severe illness following infection.

History of WNV in the United States

WNV was first reported in the United States in New York State in the summer of 1999. From 1999 to 2001 in the United States, 149 cases of illness and 18 deaths caused by WNV were reported in humans. In 2002, State health departments reported more than 4100 cases and more than 280 deaths in humans to the electronic surveillance system of the Centers for Disease Control and Prevention (CDC)*. In 2003 more than 9800 cases and 264 deaths in humans were reported.

Occupational Risks of WNV


The most likely route of WNV infection to humans is through the bite of an infected mosquito. Workers at risk of exposure to WNV include those working outdoors when mosquitoes are actively biting. Occupations at risk include farmers, foresters, landscapers, groundskeepers and gardeners, painters, roofers, pavers, construction workers, laborers, mechanics, and other outdoor workers.

Workers are at risk of WNV infection if their skin is penetrated or cut while handling WNV-infected tissues [CDC 2002c]. Turkey breeder farm workers have been infected with WNV [CDC 2003]. The mode of transmission to these farm workers is uncertain. It is recommended that workers use standard infection control and droplet precautions when working with laboratory specimens or with humans or animals suspected or known to be infected with WNV.

Workers at risk should receive training that describes and reinforces the potential occupational hazards and risks of WNV exposure and infection. The importance of timely reporting of all injuries and illnesses of suspected occupational origin should be emphasized. A medical surveillance system should be in place which includes the reporting of symptoms consistent with WNV infection, laboratory incidents or accidents involving possible WNV exposures, and employee absenteeism.

This Web page presents information about WNV relevant to occupational safety and health. Links to Federal agencies and other organizations providing comprehensive WNV information are provided.

* For updates on the geographic range of WNV, the number of human cases, and other current information link to the CDC West Nile Virus Home Page:
http://www.cdc.gov/ncidod/dvbid/westnile/

 

Updated June 7, 2004

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