West Nile Virus

West Nile virus is spread by mosquitoes and can cause illness in people and animals.  A majority of people infected with West Nile virus have no symptoms or have very mild illnesses.  About 20% of cases develop a flu-like illness, with symptoms such as fever, headache, body aches, vomiting, diarrhea, or rash.  Severe cases can develop into neuroinvasive disease, which can be fatal.

West Nile virus was found in the United States in New York City in 1999. Since then, it has spread across the continental United States. Cases have been detected in Louisiana every year since 2001, and have been identified in residents throughout the state. During West Nile Season (typically July – November), LDH issues weekly reports on current virus transmission trends here.

Infected Mosquitoes

Humans primarily become infected with West Nile virus through mosquito bites.  Mosquitoes pick up the virus by biting infected reservoir hosts, most commonly birds.  Humans are considered “dead-end hosts,” since mosquitoes cannot pick up the virus from an infected human and spread it to another human.

 

Transfusions, Transplants, Mother-to-Child

Rarely, the virus has been spread by blood transfusion, organ transplant, and from mother to child during pregnancy. Donated blood is tested for West Nile virus before being given to other patients.

West Nile virus is NOT spread by casual contact such as touching, kissing, or caring for someone who is infected.

Symptoms generally occur 2-14 days following the bite of an infected mosquito, but this incubation period can be longer for immunocompromised people.

 

Asymptomatic West Nile
About 80% of people who are infected with West Nile virus have no symptoms or experience mild illness and recover fully.  These infections are occasionally detected during blood donation testing or other routine bloodwork.

 

West Nile Fever
Up to 20% of people who are infected with West Nile virus develop West Nile Fever, a flu-like illness that causes symptoms such as fever, headache, body aches, and nausea.  Less frequently, people can also experience rashes, swollen lymph glands, or eye pain.

 

West Nile Neuroinvasive Disease
Less than 1% of individuals infected with West Nile virus develop West Nile neuroinvasive disease, a serious form of the infection that affects the nervous system. Symptoms include severe headache, high fever, stiff neck, disorientation, muscle weakness, numbness, tremors, vision loss, coma, encephalitis, meningitis, or paralysis. These symptoms can last several weeks, and can cause death or permanent damage. Older individuals are most at risk for this form of West Nile, but anyone who contracts West Nile virus has a chance of developing this most severe form.

If you are bitten by disease-carrying mosquitoes, you are at risk for West Nile virus infection. People older than 50 are more likely to become ill and develop serious symptoms.  Being outside increases your risk of being bitten by a mosquito, which increases your risk for being infected with West Nile virus. The best way to avoid West Nile is to take precautions against mosquito bites by using EPA-registered insect repellants, avoiding mosquito exposure, and reducing mosquito breeding grounds around the home.

The risk of West Nile transmission during medical procedures is extremely low, since donated blood is routinely tested before being used.

West Nile virus infection can only be diagnosed by a medical provider. If you think you have West Nile virus, you can make an appointment to see your healthcare provider. If your provider suspects that you may have West Nile virus infection, he or she will take a blood sample or draw spinal cord fluid for testing.  The most common tests for West Nile virus infection detect antibodies (IgM) that demonstrate an immune response to the virus.

 

There is no specific treatment, medication, or cure for West Nile virus. Most people who get this illness recover from it on their own. In more severe cases, people may need to go to the hospital where they can receive supportive care to treat their symptoms.

There is no vaccine for West Nile virus currently available for humans. People should protect themselves from West Nile by avoiding mosquito bites.

Research indicates that most people are not able to become infected with West Nile virus more than once. Medical tests indicate that once a person has been infected with West Nile virus, he or she develops a natural immunity to future infection for life. 

Some people who have weakened immune systems from certain conditions or medications might not have a strong immune response to the initial infection or their immunity may wane over time.  Some people with weakened immune systems may also have delayed or persistent infections.

The following are measures that can help reduce mosquitoes in and around your home:

• Install or repair window screens
• Eliminate standing water, which mosquitoes require for breeding. Dispose of water-holding containers, such as tin cans, plastic containers, ceramic pots, used tires, and tire swings.
• Pay special attention to discarded tires that may have collected on your property. Stagnant water in tires is a common place for mosquitoes to breed.
• Drill holes in the bottom of containers such as those used for recycling.
• Clean clogged roof gutters.
• Turn over objects that may trap water when not in use, such as wading pools and wheelbarrows.
• Change water in bird baths on a weekly basis. Do not allow water to stagnate in birdbaths; aerate ornamental ponds or stock them with fish.
• Clean and chlorinate swimming pools. When pools are not in use, use pool covers and drain when necessary. Be aware that mosquitoes may even breed in the water that collects on swimming pool covers.
• Use landscaping to eliminate standing water or puddles that collect on your property.

Mosquitoes feed on blood from humans and other animals, which is why they bite.

The following are measures that can help reduce bites from mosquitoes that feed on people and can cause West Nile:

• Be particularly careful at dusk and dawn, when mosquitoes are most active.
• Wear shoes, socks, long pants and long-sleeved shirts. Clothing material should be tightly woven.
• Use mosquito netting when sleeping outdoors or for baby strollers.
• Use mosquito repellent when you will be outdoors. Always use according to label instructions. The most effective repellents contain DEET, Picaridin, oil of lemon eucalyptus or IR3535.
• Always wash treated skin when returning indoors.  Do not apply repellant under clothing, to wounds or irritated skin, the hands of children, or to infants younger than two months old.
• Be sure your home's door and window screens are tight fitting and in good repair to avoid mosquitoes entering indoors.

Pets are exposed to West Nile virus through mosquito bites the same way humans are, but animals rarely get sick or show symptoms of West Nile virus infection. Concerned pet owners should consult with a veterinarian about mosquito prevention for animals. Most West Nile animal infections have been identified in birds, but West Nile virus infections have been identified in many animals, such as dogs, cats, and horses.

There is no West Nile virus vaccine currently available for dogs or cats.  There is an effective vaccine against encephalitis in horses. Horse owners should consult their veterinarians for vaccine information.

LDH does not direct mosquito spraying in the state. Local mosquito abatement districts handle mosquito spraying at the local, parish, and community levels. LDH works closely with the mosquito abatement districts and partner organizations statewide to assess West Nile virus activity.