West Nile Virus – July 2012 Update

West Nile virus (WNV) is a potentially serious illness. Experts believe WNV is established as a seasonal epidemic in North America that flares up in the summer and continues into the fall.

Top Five Tips for Camps

  1. Encourage body cover: Long pants, shirts, socks, and hats should be worn as appropriate for the weather and activity. Shirts should be tucked in at the waist; socks should be pulled over pant legs.
  2. Apply an insect repellent: Repellent containing 10 percent to 30 percent (recommended for children) to 50 percent DEET is best. Reapply per package directions throughout the duration of the activity. Wash repellent off skin when returning indoors, especially if repeated applications are used.
  3. Be on the lookout for mosquitoes: Educate staff, especially those who live with campers or who accompany groups of campers from activity to activity, to notice children who are getting bitten by mosquitoes. Assess those campers for appropriate use of their repellent.
  4. Avoid mosquito-borne habitats: Mosquitoes especially like wooded areas and marshes during the dusk and dawn periods —  peak biting time. Avoid campouts near marshes and other wet areas.
  5. Monitor and maintain activity areas: Are campers or staff commenting that mosquitoes are typically bad in certain areas?  Are puddles or standing water located near activity areas where mosquitoes might live/breed?

Background

West Nile virus was first identified in 1937 in Uganda, and then was discovered in the United States in the summer of 1999 in New York State. Since then, the virus has spread throughout the United States. It has been known to cause asymptomatic infection and fevers in humans — and sometimes death. In 2011, the Centers for Disease Control and Prevention (CDC) recorded 712 cases of WNV in the United States, with 43 of those cases resulting in death.

Transmission of West Nile Virus

WNV is most often transmitted to humans through mosquito bites; however, the virus can also be transmitted through contact with other infected animals, their blood, or other tissues. Mosquitoes become infected when they feed on infected birds that have high levels of WNV in their blood. Infected mosquitoes can then transmit WNV when they feed on humans or other animals. According to the National Institute of Allergy and Infectious Diseases, scientists have identified at least 40 mosquito species that can transmit West Nile virus. In a very small number of cases, WNV also has been spread through blood transfusions and organ transplants.

WNV is not transmitted from person to person and there is no concrete evidence that a person can get infected by handling live or dead infected birds. But, to add a further level of safety, if birds or other potentially infected animals must be handled, a protective barrier (e.g., gloves, inverted plastic bags) should be used.

Symptoms of West Nile Virus

Most WNV infected humans have no symptoms. A small proportion develops mild symptoms that include fever, headache, body aches, skin rash, and swollen lymph glands. People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito. Less than 1 percent of infected people develop more severe illness that includes meningitis (inflammation of the spinal cord) or encephalitis. The symptoms of these illnesses can include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Of the few people that develop encephalitis, a small proportion die but, overall, this is estimated to occur in less than 1 out of 1,000 infections.

In 2011, there were 712 recorded cases of West Nile Virus in the United States, with 43 of those cases resulting in death.  — Centers for Disease Control and Prevention

Treatment of West Nile Virus Infection

There is no specific treatment for WNV infection or vaccine to prevent it. Treatment of severe illnesses includes hospitalization, use of intravenous fluids and nutrition, respiratory support, prevention of secondary infections, and good nursing care. Medical care should be sought as soon as possible for persons who have symptoms suggesting severe illness.

Prevention of West Nile Virus Infection

The best way to prevent West Nile virus infection is to avoid mosquito bites. Consider the following recommendations to avoid infection:

  • When outdoors:
    • Wear clothing that covers the skin such as long-sleeve shirts and pants.
    • Apply effective (see below for details) insect repellent to clothing and exposed skin.
    • Curb outside activity during the hours that mosquitoes are feeding, which often includes dawn and dusk.
  • Drain sources of standing water in places like buckets, barrels, tires, bird baths, and such to reduce the amount of mosquitoes that breed around your area.
  • If birds or other potentially infected animals must be handled, a protective barrier (e.g., gloves, inverted plastic bags) should be used.
  • Screens should be applied to doors and windows and regularly maintained to keep mosquitoes from entering buildings.

Insect Repellents

Female mosquitoes bite people and animals because they need the protein found in blood to help develop their eggs. Mosquitoes are attracted to people by skin odors and carbon dioxide from breath. The active ingredients in repellents make the person unattractive for feeding. Repellents do not kill mosquitoes. Repellents are effective only at short distances from the treated surface, so you may still see mosquitoes flying nearby. The CDC recommends using products that have been shown to work in scientific trials and that contain active ingredients which have been registered with the U.S. Environmental Protection Agency (EPA) for use as insect repellents on skin or clothing. Of the active ingredients registered with the EPA, the CDC believes that two have demonstrated a higher degree of efficacy in the peer-reviewed, scientific literature. Products containing these active ingredients typically provide longer-lasting protection than others:

  • DEET (N,N-diethyl-m-toluamide)
  • Picaridin (KBR 3023)

Oil of lemon eucalyptus [active ingredient: p-menthane 3,8-diol (PMD)], a plant- based repellent, is also registered with EPA. In two recent scientific publications, when oil of lemon eucalyptus was tested against mosquitoes found in the U.S., it provided protection similar to repellents with low concentrations of DEET.

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