What is West Nile Virus?

Kristen Healy, Morgan, Alan L.

West Nile virus is a mosquito-borne disease that can cause encephalitis, or a brain infection. Mosquitoes acquire the virus from birds and pass it on to other birds, animals and people.

Mosquitoes spread this virus after they feed on infected birds and then bite people, other birds and animals. It is not spread by person-to-person contact and there is no evidence that people can get the virus by handling infected animals

Surveillance for WNV was initiated in Louisiana in the Spring of 2000 and currently involves the reporting and testing of dead birds, and the testing of sick horses, mosquito pools and sentinel chicken flocks.

Louisiana has four kinds of Encephalitis: West Nile Encephalitis, Saint Louis Encephalitis (SLE), Eastern Equine Encephalitis (EEE) and LaCrosse-California Encephalitis.

West Nile virus cases occur primarily in the late summer or early Fall, although the mosquito season is April through October.

What is an Arboviral Encephalitis?

An Arboviral Encephalitis is an infectious disease that affects the brain. The disease is caused by a virus which attacks the brain, destroys some nerve cells and causes brain inflammation and swelling. Encephalitis arboviruses belong to several families of viruses that usually infect birds and are transmitted from bird to bird by mosquitoes. The name "ar-bo-virus" comes from the fact that they are transmitted by arthopods (insects and other "bugs").

What is West Nile encephalitis?

West Nile encephalitis (WNE) is caused by West Nile virus (WNV), a flavivirus previously only found in Africa, Eastern Europe, and West Asia. WNV is closely related to St. Louis encephalitis virus (SLEV) which is found in the United States and to the Japanese Encephalitis virus in South East Asia, the Murray Valley fever virus in Australia and New Guinea.

The majority of the people who get infected with the virus have no illness or at most, have an infection similar to a mild flu with fever, headache and fatigue. Rarely, will the virus multiply in the central nervous system and cause the brain disease called encephalitis.

How can I get it?

The principle route of human infection is through the bite of an infected mosquito. 

In 2002, additional routes have become apparent, however this represents a very small proportion of cases.  These routes include receiving transplanted organs and blood transfusions, transplacental and possibly breastfeeding transmission, and laboratory workers working with WN-infected products.

Who is most at risk?

People over 50 years of age have the highest risk of developing a severe illness because as we age, our bodies have a harder time fighting off disease. People with compromised immune systems are also at increased risk. However, anyone can get the virus.

What are the symptoms?

People with mild infections may experience fever, headache, body aches, skin rash and swollen lymph glands, this is called West Nile Fever. People with more severe infections may experience high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions and paralysis, this is called West Nile Encephalitis. If you have any of these symptoms, contact your doctor.

Are there long-term consequences?

While most infections are usually mild, West Nile Encephalitis can result in death or serious brain damage. Some improvements may be seen after some time.

Is there treatment or a vaccine?

There is no specific treatment for West Nile virus infection, nor a vaccine. While most people fully recover from the viral infection, in some severe cases hospitalization may be needed.

How can I protect myself?

It is not necessary to limit any outdoor activities, unless local officials advise you otherwise.

However, you can and should try to reduce your risk of being bitten by mosquitoes. In addition to reducing standing water in your yard, make sure all windows and doors have screens, and that all screens are in good repair.

If West Nile virus is found in your area:

  • When outdoors, wear a mosquito repellent containing 20 -30% DEET for adults and no more than 10% for children. Do not use repellent containing DEET on children under 3 years of age. Follow the label's instructions carefully, especially when applying to children. Wash all skin and clothing when returning indoors to remove insect repellent. Do not spray repellant in enclosed areas.
  • Only adults should apply repellent on a child.
  • Spray repellent on your hands and then apply to your face.
  • Only apply repellent to exposed skin and clothing.
  • After returning indoors, wash treated skin with soap and water.
  • Do not use repellent under clothing.
  • Wash treated clothing before wearing it again.
  • Do not apply repellent over cuts, wounds, sunburn or irritated skin.
  • Wear long-sleeved shirts and pants when outdoors for long periods of time.
  • Avoid perfumes and colognes when outdoors for extended periods of time.
Remember, electromagnetic and ultrasound devices and Vitamin B are not effective in preventing mosquito bites.

Where do I call/go if I need more information about West Nile virus?

You can call the Office of Public Health, Infectious Disease Epidemiology at 1-800-256-2748 and speak to the epidemiologist on call, he or she will be able to answer general questions about the virus but will NOT be able to make a medical diagnosis.  You can also contact your physician or local Parish Health Unit.  Your physician is the best person to discuss your health and to decide if a test is necessary.

Is my pregnancy at risk if I get infected?

There has been one documented case of transplacental (mother-to-child) transmission.  This newborn was also born with severe medical problems and it is unknown whether the West Nile infection contributed to these problems or was coincidental.

Pregnant women, like everyone else, should focus on reducing their exposure by avoiding mosquitoes, wearing long sleeves and pants when outside and wearing repellants containing DEET.

What about breastfeeding?

Because the health benefits of breastfeeding are well established, and the risk for WNV transmission through breastfeeding is unknown, no change in breastfeeding habits is recommended.  Lactating women who are ill or are having difficulty breastfeeding for any reason, as always, are advised to consult their physicians.

Can women who are pregnant or breast-feeding use insect repellent with DEET?

Yes.  Insect repellents help protect people from mosquito bites that may carry potentially serious viruses such as West Nile virus, while allowing them to continue to play and work outdoors. There are no reported side-effects from the use of repellents containing DEET in pregnant or breast-feeding women.   Other ways to limit exposure to mosquitoes include limiting time outside especially during dawn and dusk, and wearing long sleeves and pants.

Should I avoid donating blood or getting blood transfusions or organ transplants?

No.  Donating blood is safe, and we encourage blood donation now and in the future. Although persons needing blood transfusions or organ transplants should be aware of the risk for WNV infection, the benefits of receiving needed transfusions or transplants outweigh the potential risk for WNV infection.

Can I still donate blood if I have had West Nile virus?

A person who has had West Nile virus can still donate blood after they completely recover.  Blood centers take precautions to be sure that donors who have been diagnosed with West Nile virus have fully recovered before donating.

Where do mosquitoes breed?

There are about 60 different species of mosquitoes in Louisiana. While most do not transmit West Nile virus, several mosquito species have been found to transmit the virus.

Some mosquitoes lay their eggs in stagnant water around the home. Weeds, tall grass, shrubbery and discarded tires also provide an outdoor home for adult mosquitoes. By eliminating places for mosquitoes to breed, we can go a long way to prevent West Nile virus.

How can I reduce the number of mosquitoes around my home and neighborhood?

Mosquitoes breed in standing water. Even a small bucket that has stagnant water in it for seven days can become home to up to 1,000 mosquitoes. Here are some easy tips to eliminate standing water:

  1. Dispose of tin cans, plastic containers, ceramic pots or similar water holding containers that have accumulated on your property. Do not overlook containers that have become overgrown by aquatic vegetation.
  2. Pay special attention to discarded tires that may have accumulated on your property.
  3. Drill holes in the bottom of recycling containers that are left out of doors. Drainage holes that are located on the container sides collect enough water for mosquitoes to breed in.
  4. Clean clogged roof gutters on an annual basis, particularly if the leaves from surrounding trees have a tendency to plug up the drains. Roof gutters are easily overlooked but can produce millions of mosquitoes each season.
  5. Turn over plastic wading pools when not in use. A wading pool becomes a mosquito producer if it is not used on a regular basis.
  6. Turn over wheelbarrows and do not allow water to stagnate in birdbaths. Both provide breeding habitat for domestic mosquitoes.
  7. Aerate ornamental pools or stock them with fish. Water gardens are fashionable but become major mosquito producers if they are allowed to stagnate. Clean and chlorinate swimming pools that are not being used. A swimming pool that is left untended by a family that goes on vacation for a month can produce enough mosquitoes to result in neighborhood-wide complaints. Be aware that mosquitoes may even breed in the water that collects on swimming pool covers.
  8. Use landscaping to eliminate standing water that collects on your property. Mosquitoes will develop in any puddle that lasts for more than four days.

What about dead birds?

Dead birds can be an indication that West Nile virus is present in an area, particularly blue jays, crows, cardinals, grackles, house sparrows, birds of prey, and seagulls.

How do I report a dead bird?

For tracking purposes, we are asking the public to continue to report all dead birds to their local Parish Health Unit. After hours and on weekends, call the toll-free hotline at 800-256-2748, press 3 to report a dead bird (this may cause some delay in reporting). Dead birds provide an effective early warning system for the detection of West Nile Virus before it is transmitted to humans.

How do I collect a dead bird?

OPH is collecting blue jays, crows, cardinals, grackles, house sparrows, birds of prey, and seagulls. Due to limited funding the collection and testing of birds is targeted to the types that provide the most reliable information.

The CDC advises that there is no danger of contracting WNV from handling intact dead birds. The following procedure is suggested when collecting a specimen and when handling any dead animals:

  • Turn a plastic bag inside-out, and pick up the bird with the hands protected by the bag.
  • Turn the bag right-side-out. The bag should then be tied or sealed and placed inside another plastic bag.
  • Another method is to wear disposable gloves or small plastic bags over the hands, to protect the hands while placing the bird in a double plastic bag.

If submitting for testing, keep the bird in a freezer or cooler with ice. Otherwise, the bird can be disposed of in the regular hospital trash.

Where else has West Nile virus been found?

Prior to 1999, no West Nile virus cases had been reported in the United States but the virus had a wide distribution in Africa, Asia, the Middle East and Europe and caused occasional epidemics.  In 1999, the virus appeared in New York City, and was responsible for an encephalitis outbreak causing 62 cases and 7 deaths.

Between 2000 and 2002, the presence of West Nile expanded from the Northeastern US to the South Central states and westward, appearing in the Pacific coast for the first time in 2002.  In 2002, West Nile activity was reported in 44 states and the District of Columbia compared with 27 states and DC in 2001, 12 states and DC in 2000 and 4 states in 1999. (Maps are available on the CDC West Nile Virus page, “Statistics, Surveillance, and Control”)  

The number of reported cases was relatively small in 2000 and 2001 (21 in 2000, 66 in 2001) however in 2002, the number of cases increased dramatically and greatly expanded in geographic range (to date, 4071 reported cases with 275 deaths). The 2002 West Nile epidemic was the largest West Nile epidemic ever reported and the largest of any reported arboviral meningoencephalitis in the Western Hemisphere.

In Louisiana, 329 West Nile Fever and meningoencephalitis cases were reported from 41 parishes.

10/4/2004 4:27:41 AM
Rate This Article:

Have a question or comment about the information on this page?

Innovate . Educate . Improve Lives

The LSU AgCenter and the LSU College of Agriculture