West Nile Virus

Klamath County Department of Public Health 

West Nile Virus  

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Information from:
1. Centers for Disease Control and Prevention
2. Oregon Acute and Communicable Disease Prevention
3. MayoClinic.com

West Nile virus is a mosquito-borne virus that can cause symptoms of varying severity in humans. The virus is closely related to viruses that cause St. Louis encephalitis, the most common mosquito-borne encephalitis in the United States, and Japanese encephalitis.

Most people with WNV may not have symptoms or have only a mild illness. However, the illness caused by West Nile virus may be serious and may include encephalitis, inflammation of the brain, or meningitis.

West Nile virus is relatively new to the United States, making its first known appearance in August 1999 during an outbreak in New York City. Since then, it has spread rapidly to more than 40 states, infecting birds, humans and horses. In 2005 the Centers for Disease Control (CDC) reported 3,000 human infections in the United States.

Most people who become infected with West Nile virus don't become seriously ill and recover fully. You can reduce your risk of contracting West Nile virus by avoiding exposure to mosquitoes.

How is West Nile virus transmitted?

The principal transmission cycle of West Nile virus involves several species of mosquitoes and various species of birds. Mosquitoes become infected with West Nile virus when they feed on a bird carrying the virus in its blood. After 10 to 14 days, the virus can be transmitted to another bird, person, or other animal that the mosquito bites. During blood feeding the mosquito injects the virus, contained in its saliva, into the bird, animal, or person - where the virus replicates and may cause illness.

Although humans and some other animals may get sick when infected with West Nile virus, it is thought that they usually do not develop enough virus in the bloodstream to infect mosquitoes. For this reason, humans and animals such as horses are referred to as incidental hosts. West Nile virus is generally not spread from person to person.  However, in a very small number of cases, it has been transmitted through blood transfusions, organ transplants, breastfeeding, and even during pregnancy from mother to baby.  It is not transmitted by casual contact such as kissing or touching.

The main role that people play in contributing to the continuing cycle of West Nile virus is by maintaining environments (especially standing water) in which mosquitoes can lay eggs.

What are the symptoms of West Nile virus infection?

Most people who are infected with West Nile virus will not develop symptoms. Some people may become ill 3 to 15 days after the bite of an infected mosquito.

Common signs and symptoms of West Nile virus infection include:

West Nile virus infection infrequently results in a severe illness, however, known as West Nile encephalitis. Encephalitis is an inflammation of the brain that may be marked by:

A small number of cases have been fatal.

Photo courtesy Centers for Disease Control & Prevention, photographer Jim Gathany
 

Who is at risk for West Nile virus infection?

People are only at risk for becoming infected with West Nile virus when in areas where the virus is circulating in nature. The risk of West Nile virus is seasonal and begins in spring, with the peak time for infection in mid to late August.

The risk of developing a serious West Nile virus-related illness after being bitten by an infected mosquito is less than 1 percent. In most cases people who become infected with the virus recover fully.

Anyone bitten by an infected mosquito is at risk of acquiring the virus, although the risk of severe infection is greatest for people who are over age 50 or who have a weakened immune system.

There is no documented evidence that a pregnancy is at risk due to a mother's infection with West Nile virus.

When to seek medical advice

See your doctor as soon as possible after you experience signs and symptoms that might suggest West Nile encephalitis. Although most people infected with the virus recover fully, the virus can result in serious, life-threatening illness.

Screening and Diagnosis

Your doctor can confirm the presence of West Nile virus in your body by drawing a sample of your blood to be analyzed in the laboratory. If you have West Nile virus, an analysis of your blood sample may show:

If your doctor suspects that West Nile virus has caused you to have meningitis or encephalitis, he/she may conduct the following diagnostic test:

How is West Nile virus infection treated?

There is no vaccine or specific treatment available for infection with West Nile virus. In the case of West Nile encephalitis, intensive support therapy may be required - such as hospitalization, intravenous fluids, respiratory support (ventilator), prevention of secondary infections (such as pneumonia, urinary tract infections, etc.) and good nursing care.

What can we do to prevent West Nile infection?

Avoid mosquito bites

Apply an insect repellent that contains 20 percent to 30 percent DEET to exposed skin when you go outdoors. The more DEET a repellent contains, the longer time it gives protection from mosquito bites.  Other effective repellents include Picaradin, and EPA-registered oil of lemon eucalyptus preparations.

Whenever possible, wear protective clothing such as long sleeves, long pants and socks when outdoors.

Spray clothing with repellents containing DEET, because mosquitoes may bite through thin clothing.

Consider staying indoors between dusk and dawn, which is peak mosquito biting time. Avoid activities in areas where mosquitoes are plentiful.

Fix or install window and door screens to keep mosquitoes out of buildings.

Always read and follow the product directions when using any insect repellent or insecticide!

Avoid breeding mosquitoes

Mosquitoes lay their eggs in standing water. To avoid helping mosquitoes breed in your environment, drain standing water. Routinely empty water from flower pots, pet bowls, clogged rain gutters, swimming pool covers, discarded tires, buckets, barrels, cans and other items that collect water in which mosquitoes can lay eggs.

Do animals get sick from this virus?

In 2005, 1075 cases of West Nile virus in horses were reported from 36 states.  Small numbers of other animal species such as squirrels, alligators, dogs, sheep, and llamas have tested positive for WNV in past years.

Do birds get sick from this virus?

Yes, several hundred dead birds tested positive in 1999 and several thousand in 2000.

Who do I call about a sick bird or other animal in Oregon?

If you find a single dead or ill bird from the corrid family, i.e. a blue jay, magpie, crow, or raven, please call Klamath Vector Control at (541) 882-2715 or Klamath County Health Department at (541) 882-8846.  DO NOT HAND THE BIRD DIRECTLY.  In case of a large or continuous die-off, and you are concerned about West Nile virus, please contact your local county health department or the local Fish and Wildlife Office for information.

Where can I get more information?

For additional information, you can call the Oregon Health Services at 1-866-703-4636 or log on at http://oregon.gov/DHS/ph/acd/diseases/wnile/survey.shtml.