West Nile virus

The West Nile virus is a mosquito-borne virus that can cause mild to severe illness.


Causes/associated factors
Birds are the major carrier of the West Nile virus. Mosquitoes that bite and feed on these birds may become infected and, in turn, transmit the virus to other birds, animals and people. Viruses that spread through the bite of a mosquito or other arthropod are known as arboviruses.
The West Nile virus was first identified in the United States in New York in 1999. Since then, it's been found in mosquitoes, birds, animals or people in all states except Hawaii, Alaska and Oregon.

Even if you live in an infected area, the risk of becoming ill with a West Nile infection is small. Less than 1 percent of mosquitoes are infected with the virus. About 20 percent of people infected with the virus develop a mild illness. An estimated one in 150 people who become infected become seriously ill. West Nile infections are most common in people older than age 50, who are also at greater risk of severe or even fatal complications.


Transmission
The West Nile virus has been found in more than 130 species of birds in the United States. The virus is most deadly for crows and blue jays. Mosquitoes become infected when they bite an infected bird. The virus may then spread to people and other animals -- including birds, horses, cats, bats, chipmunks, skunks, squirrels and domestic rabbits -- through the bite of an infected mosquito.
The West Nile virus doesn't appear to spread through contact with an infected animal. It doesn't spread from person to person, except rarely from mother to baby during pregnancy or breastfeeding.

Transmission to recent organ transplant and blood transfusion recipients has been reported. New screening methods are now in place to reduce the risk of spreading the virus through transfusions. Screening methods for organ donation are being evaluated.

The incubation period (time from the mosquito bite to the appearance of symptoms) ranges from three to 14 days.

In the temperate climate of the United States, West Nile infections are most common in late summer and early fall, when mosquitoes are more active. In tropical climates, the virus can spread at any time.


Signs/symptoms
About 80 percent of people who are infected with the West Nile virus develop no symptoms. When symptoms do appear, they're often mild and flu-like, including fever, headache, body aches, nausea and vomiting. Occasionally there are swollen glands or a rash on the trunk of the body. This infection, referred to as West Nile fever, generally lasts three to six days.
In more severe cases -- affecting less than 1 percent of infected people -- the virus may cause:

West Nile encephalitis (inflammation of the brain)
meningitis (inflammation of the membrane surrounding the brain and spinal cord)
meningoencephalitis (inflammation of the brain and the surrounding membrane)
Symptoms of more severe disease may include high fever, severe headache, stiff neck, confusion, tremors, seizures, muscle weakness, paralysis or coma. In some cases, West Nile encephalitis may be fatal.


Diagnosis
Diagnosis is initially based on your medical history, current symptoms and a physical exam. If you live in an area with West Nile virus activity and have symptoms of possible infection, your doctor may test your blood for virus antibodies (compounds that help neutralize or destroy foreign substances in the blood).

Treatment
There's no specific treatment for a West Nile virus infection. The U.S. Food and Drug Administration (FDA) has approved a clinical trial to test alpha interferon as a possible treatment, however. In addition, the National Institute of Allergy and Infectious Diseases (NIAID) is currently enrolling patients in a clinical trial to test the effectiveness of an intravenous immunoglobulin that contains antibodies to the West Nile virus in preventing death or disability from West Nile encephalitis.
Meanwhile, treatment focuses on supportive care and easing the symptoms. If the infection is severe, hospitalization may be needed. In the hospital, treatment may include intravenous fluids, breathing support and medication to control symptoms such as pain, fever, brain swelling and seizures. Medication to treat or prevent associated infections, such as pneumonia, may also be needed.


Complications
Complications of West Nile encephalitis may include mental deterioration, seizures and coma. Permanent neurological damage can occur, and a few cases of polio-type paralysis have been reported. In some cases, encephalitis is fatal.

Pregnancy-specific information
To protect yourself from the West Nile virus, do your best to avoid mosquitoes. When you must be outdoors, wear protective clothing and use insect repellent as directed by your doctor. Follow the product instructions carefully.
Rarely, West Nile virus may spread from mother to baby during pregnancy or breastfeeding. The potential effect on the baby is being studied. If you develop a West Nile infection during pregnancy, your doctor will report it to the state or local health department or the Centers for Disease Control and Prevention.


Senior-specific information
Adults older than age 50 have the highest risk of developing serious and sometimes fatal illness from the West Nile virus. People who have diabetes or weak immune systems also have an increased risk of serious illness.

Prevention
A vaccine to prevent West Nile infections is being developed. In the meantime, consider these tips to prevent the spread of the virus:
Decrease the number of mosquitoes around your home by keeping plants trimmed and removing all plant debris from the area.

Eliminate mosquito breeding grounds by emptying any standing water from containers such as pots, cans and tires.

Keep wading pools and other containers turned over when not in use.

Change the water in birdbaths at least every three to four days.

Keep your roof gutters cleaned and draining properly.

Keep mosquitoes out of your home with intact screens on all doors and windows.
To avoid contact with mosquitoes, keep the following considerations in mind:

Stay indoors or in screened-in areas as much as possible when mosquitoes may be present, especially at dawn, dusk and in the early evening.

When outdoors during periods of mosquito activity, use insect repellent and wear long-sleeved shirts, long pants, shoes and socks. Avoid bright colors and scented products such as perfume, soap, lotion and aftershave. Avoid scented hair spray and deodorant.

When applying any insect repellent, carefully follow the directions on the product label. Diethyltoluamide (DEET) is a common ingredient in insect repellents that deter mosquitoes. If you're using a topical prescription medication, check with your doctor before using DEET.
Depending on the product, concentrations of DEET range from 4 to 100 percent. Products containing higher concentrations of DEET generally provide longer-lasting protection. This protection seems to peak at concentrations of about 30 to 50 percent. Higher concentrations are sometimes used in special situations, such as in areas where there's a high risk of infection spread through biting insects. Extended-release formulas reduce the concentration while extending the duration of protection. Most of the commercial products available contain 40 percent or less DEET.

Although there haven't been any adverse effects to insect repellent reported from women who are pregnant or breastfeeding, check with your doctor before using any medications or products such as insect repellent while you're pregnant or breastfeeding.

The best approach is to use the lowest concentration of DEET effective for the amount of time spent outside:


30-percent DEET protects for six hours
24-percent protects for five hours
20-percent protects for four hours
6.65-percent protects for two hours
4.75-percent protects for an hour and a half

Even for children, products containing DEET are the most effective insect repellents. The safety of DEET doesn't appear to be related to the concentration in the repellent. There are no studies on skin absorption of DEET in children, but studies of similar substances suggest that absorption through the skin wouldn't differ after age 2 months. Currently, 30-percent DEET is the maximum concentration recommended for infants and children older than age 2 months. Again, the concentration of DEET used is based on the time the child is expected to be outside. Keep insect repellent out of reach of children at all times.
Don't let your child touch the repellent or apply it himself or herself. Discourage children from licking areas of their skin treated with DEET. Kids often have a tendency to put their hands in their eyes and mouths, so discourage them from touching any skin treated with DEET as much as possible.


Only apply the repellent to exposed areas of the skin, using as little as possible. Heavy applications don't provide increased protection. Apply sparingly to exposed skin folds, and don't apply under clothing. Don't use products containing DEET under diapers or in areas of skin-to-skin contact, such as the groin area, the front of the elbows or the backs of the knees. Using DEET in these areas may cause the skin to become red, painful or blistered.

Don't inhale or ingest DEET products. Don't spray it in enclosed areas or apply it near food. Wash your hands before eating.

Use caution when applying the repellent to your face. Keep the product out of your eyes, nose and mouth area. Don't spray aerosol products directly onto your face. Instead, spray the repellent on your hands and apply it gently to your face. Don't apply repellent to the hands or faces of children of any age.

Don't apply products containing DEET to injured, irritated or sunburned skin. This increases the risk of absorption through the skin.

Generally, DEET shouldn't be applied more than once a day. If you're outside for longer than expected and are being bitten, however, you can reapply repellent. Also, sweating, perspiration or getting wet may require reapplying repellent, but do so only if you're being bitten.

Read product labels before applying anything containing DEET to surfaces such as fabrics or upholstery. DEET doesn't typically damage natural fibers, but it may harm leather, synthetics, plastics, eyeglass frames, watch crystals, and painted or varnished surfaces (including automobiles).

Follow fire safety measures if the product contains alcohol, which is flammable.

When protection is no longer needed, remove the product from your skin with soap and water. Do the same for your children. Wash any clothing that's been sprayed with DEET before wearing again.

You can also apply Permethrin, an EPA-approved insecticide that works to kill insects rather than repel them. Permethrin isn't applied to your skin. Instead, it's applied to your clothing and shoes to kill ticks. The product retains its effectiveness for up to two weeks, despite as many as five launderings. The risk of adverse effects is low because Permethrin isn't readily absorbed by the skin. Check with your doctor before using any insecticides if you're pregnant or breastfeeding.

If you live in an area where the West Nile virus has been documented, report any dead birds to the local health department.

Consider contacting your local mosquito control program for assistance or questions regarding control of mosquito populations, especially if treatment of ponds and other wetlands may be needed.