West Nile Virus

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A Field Worker’s Guide to Reduce Exposure

In the coming months, West Nile Virus will be in the news. It is important for Field Workers to learn about any new information concerning this virus – the media can be a good source of information on the spread of WNV across Canada. There are many good web-sites to find information on WNV.

What is WEST NILE Virus?

West Nile Virus is one of a variety of mosquito-borne viruses that can cause infection in humans and animals. The following link offers more information on the West Nile Virus transmission cycle: http://www.cdc.gov/ncidod/dvbid/westnile/birds&mammals.htm

What are the symptoms associated with a West Nile Virus Infection?

The WNV normally cycles between mosquitoes and birds. However, if a person or animal is bitten by a WNV-infected mosquito, the virus may be transmitted to them. Most people who are infected with West Nile Virus will not have any type of illness. It is estimated that 20% of the people who become infected will develop West Nile Fever; mild symptoms include fever, headache, body aches, and occasionally skin rash and swollen lymph glands. More severe infection (West Nile encephalitis or meningitis) include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis and, in rare cases, death. . These severe cases are rare in humans.

How do you catch West Nile Virus?

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. Workers at risk of exposure to WNV include those working outdoors when mosquitoes are actively biting. Occupations at risk include farmers, foresters, landscapers, groundskeepers, painters, roofers, pavers, construction workers, and other outdoor workers. The following web-site offers more information on possible transmission vectors: http://www.cdc.gov/ncidod/dvbid/westnile/q&a.htm

Which Animals are infected by West Nile Virus?

Birds of the Corvid family (crows, magpies, ravens, blue jays and grey jays) are susceptible. Surveillance efforts will focus mainly on dead birds which belong to the family known as corvids. Although other bird species in the northeastern United States have become infected with WN virus, experience from the 1999, 2000 and 2001 outbreaks has shown that corvids are the most reliable indicators of WN virus activity and the potential for human infection in an area. The following web-site has more information on vertabrate ecology: http://www.cdc.gov/ncidod/dvbid/westnile/birds&mammals.htm Horses are also at risk of infection. The Canadian Food Inspection Agency, in cooperation with veterinarians and other members of the animal health community across the country, will take the lead in monitoring for WN virus infection in horses.

How can you protect yourself from getting West Nile Virus?

One of the best ways to protect yourself is to stay informed. Look up information regarding WNV and keep informed as to where the virus has spread. There are web-links listed at the end of this report.

Many mosquitoes bite people most actively at dusk and 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.

Most mosquitoes are not infected: less than 1% of the mosquito population will carry WNV. The chance that any one bite will be from an infected mosquito is very small. You can reduce your risk of disease by reducing mosquito bites. Precautions that you can follow to help reduce the risk of mosquito bites include:

  • As much as possible try to reduce mosquito-breeding areas by making sure that you have eliminated any pools of standing water in close proximity to the work area. Mosquitoes can reproduce in 4 days if there is standing water available.
  • Wear high top boots, double layers of long pants with the bottoms sealed or taped off or tucked into boots or socks, and a long-sleeved hooded top when outdoors for long periods of time, or when many mosquitoes are most active (between dusk and dawn). Wear gloves to protect the hands.
  • Hats with netting can protect the head and face area and eliminate the need of using mosquito repellent on the face and head areas.
  • Use mosquito repellent according to label directions when outdoors for long periods of time and when mosquitoes are most active.

Insect repellents can be effective at reducing bites from ticks and insects that can transmit disease. But their use is not without risk of health effects, especially if repellents are applied in large amounts or improperly. Most repellent products contain the active ingredients permethrin or DEET. Permethrin-containing products can be used only on clothing, not skin. Permethrin kills ticks and insects that come in contact with treated clothes. Permethrin repellents can cause eye irritation, particularly if label directions have not been followed. Animal studies indicate that permethrin may have some cancer-causing potential. DEET products have occasionally been associated with skin reactions (particularly at concentrations of 50 percent and above) and eye irritation. Under demanding conditions, a two-part approach has been used to protect people from ticks and other biting insects. The approach uses a repellent product containing about 33 percent DEET in a controlled-release formulation on exposed skin along with clothing treated with permethrin. This may meet the needs of individuals spending long periods of time in areas with high populations of active mosquitoes.

The following web site offers important information on the use of insect repellents: http://www.cdc.gov/westnile/faq/repellent.html

When using an insect repellent, use only what and how much you need for your situation; depending on your job, you may need more or less protection. Do not apply insect repellents in enclosed areas. Wash treated clothing separately and wash all treated skin after returning indoors. When using DEET, put it on your hands first, and then apply to your face. DEET can be applied to clothing, but it may damage some synthetic fabrics and plastics. You should wash clothes sprayed with mosquito repellent every day.

Permethrin-treated clothing is effective for two weeks or more; keep treated clothing in a plastic bag when not in use.

If you wear a long-sleeved shirt, long pants, shoes, and socks to reduce the risk of mosquito bites, you may be at greater risk for heat stress on hot, humid days. To avoid symptoms of heat stress, you should wear light-colored, breathable clothing that allows moisture to evaporate quickly and use extra caution if you are required to wear clothing on the job that limits evaporation–you could develop heat stress much more quickly. Also, drink plenty of non-alcoholic and non-caffeinated liquids to maintain body hydration.

DEET (N,N-diethyl-m-touamide or N,N-diethyl-3-methylbenzamide) is the most effective insect repellent available. However, because of health concerns, products containing DEET above 30% will no longer be available to the consumer after December 2004. Studies have shown that products with lower concentrations of DEET are just as effective as the high concentration products, but their effectiveness lasts for shorter periods of time. A product containing:

  • 30% DEET will provide approximately 6.5 hours of protection
  • 15% DEET will provide approximately 5 hours of protection
  • 10% DEET will provide approximately 3 hours of protection
  • 5% DEET will provide approximately 2 hours of protection

Choose the best product for your situation. There are extra precautions when using insect sprays on children and infants and pregnant women. Check the links list above for more information on insect repellents.

The following web sites have information on the West Nile Virus. You should stay informed and keep a close watch on where the virus is known to be present. If you are working in an area where WNV is active, take all precautions to reduce your chance of mosquito bites.