Ad

West Nile virus (WNV)

West Nile virus (WNV) is most commonly transmitted to humans by mosquitoes. You can reduce your risk of being infected with WNV by using insect repellent and wearing protective clothing to prevent mosquito bites. There are no medications to treat or vaccines to prevent WNV infection. Fortunately, most people infected with WNV will have no symptoms. About 1 in 5 people who are infected will develop a fever with other symptoms. Less than 1% of infected people develop a serious, sometimes fatal, neurologic illness.

What is West Nile virus?

West Nile virus is an arthropod-borne virus (arbovirus) most commonly spread by infected mosquitoes. West Nile virus can cause febrile illness, encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord).

West Nile virus transmission has been documented in Europe and the Middle East, Africa, India, parts of Asia, and Australia. It was first detected in North America in 1999, and has since spread across the continental United States and Canada.

Symptoms

No symptoms in most people. Most people (70-80%) who become infected with West Nile virus do not develop any symptoms.

Febrile illness in some people. About 1 in 5 people who are infected will develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with this type of West Nile virus disease recover completely, but fatigue and weakness can last for weeks or months.

Severe symptoms in a few people. Less than 1% of people who are infected will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues).

  • The symptoms of neurologic illness can include headache, high fever, neck stiffness, disorientation, coma, tremors, seizures, or paralysis.
  • Serious illness can occur in people of any age. However, people over 60 years of age are at the greatest risk for severe disease. People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk for serious illness.
  • Recovery from severe disease may take several weeks or months. Some of the neurologic effects may be permanent.
  • About 10 percent of people who develop neurologic infection due to West Nile virus will die.

Treatment

  • No vaccine or specific antiviral treatments for West Nile virus infection are available.
  • Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms
  • In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.

More detailed information can be found on our page for health care providers.

How do people get infected with West Nile virus?

Most people get infected with West Nile virus by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans and other animals.

In a very small number of cases, West Nile virus has been spread through blood transfusions, organ transplants, and from mother to baby during pregnancy, delivery, or breastfeeding.

Who is at risk for infection with West Nile virus?

Anyone living in an area where West Nile virus is present in mosquitoes can get infected. West Nile virus has been detected in all lower 48 states (not in Hawaii or Alaska). Outbreaks have been occurring every summer since 1999. The risk of infection is highest for people who work outside or participate in outdoor activities because of greater exposure to mosquitoes.

Is there a vaccine available to protect people from West Nile virus?

No. Currently there is no West Nile virus vaccine available for people. Many scientists are working on this issue, and there is hope that a vaccine will become available in the future.

How soon do people get sick after getting bitten by an infected mosquito?

The incubation period is usually 2 to 6 days but ranges from 2 to 14 days. This period can be longer in people with certain medical conditions that affect the immune system.

What are the symptoms of West Nile virus disease?

No symptoms in most people. Most people (70-80%) who become infected with West Nile virus do not develop any symptoms.

Febrile illness in some people. About 1 in 5 people who are infected will develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with this type of West Nile virus disease recover completely, but fatigue and weakness can last for weeks or months.

Severe symptoms in a few people. Less than 1% of people who are infected will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues). The symptoms of neurologic illness can include headache, high fever, neck stiffness, disorientation, coma, tremors, seizures, or paralysis.

Recovery from severe disease may take several weeks or months. Some of the neurologic effects may be permanent. About 10 percent of people who develop neurologic infection due to West Nile virus will die.

Who is at risk for serious illness if infected with West Nile virus?

Serious illness can occur in people of any age. However, people over 60 years of age are at the greatest risk for severe disease. People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk for serious illness.

What should I do if I think a family member might have West Nile virus disease?

Consult a healthcare provider for evaluation and diagnosis.

How is West Nile virus disease diagnosed?

Diagnosis is based on a combination of clinical signs and symptoms and specialized laboratory tests of blood or spinal fluid. These tests typically detect antibodies that the immune system makes against the viral infection.

What is the treatment for West Nile virus disease?

There are no medications to treat or vaccines to prevent West Nile virus infection. Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms.

People with milder symptoms typically recover on their own, although some symptoms may last for several weeks.

In more severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.

When do most cases of West Nile virus disease occur?

Most people are infected from June through September.

Where do most cases of West Nile virus disease occur?

West Nile virus disease cases have been reported from all 48 lower states. The only states that have not reported cases are Alaska and Hawaii. Seasonal outbreaks often occur in local areas that can vary from year to year. The weather, numbers of birds that maintain the virus, numbers of mosquitoes that spread the virus, and human behavior are all factors that can influence when and where outbreaks occur.

How can people reduce the chance of getting infected?

The most effective way to avoid West Nile virus disease is to prevent mosquito bites:

  • Use insect repellents when you go outdoors. Repellents containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus and para-menthane-diol products provide longer-lasting protection.
  • Wear long sleeves and pants from dusk through dawn when many mosquitoes are most active.
  • Install or repair screens on windows and doors. If you have it, use your air conditioning.
  • Help reduce the number of mosquitoes around your home. Empty standing water from containers such as flowerpots, gutters, buckets, pool covers, pet water dishes, discarded tires, and birdbaths.

Why do my state health department and CDC sometimes report different numbers of West Nile virus cases?

The CDC case count is based on the number of cases that have been reported by each state health department to CDC. The CDC case count is updated once a week during the transmission season. State health departments might update their counts more often.

Which mosquito repellents work best?

CDC recommends the use of products containing active ingredients which have been registered with the U.S. Environmental Protection Agency (EPA) for use as repellents applied to skin and clothing.

Of the products registered with the EPA, those containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus and para-menthane-diol products provide longer-lasting protection.

EPA registration means that EPA does not expect the product to cause adverse effects to human health or the environment when used according to the label.

How often should repellent be reapplied?

Repellents containing a higher percentage of the active ingredient typically provide longer-lasting protection. Regardless of what product you use, if you start to get mosquito bites, reapply the repellent according to the label instructions.

What precautions should I follow when using repellents?

Always follow the recommendations appearing on the product label. EPA recommends the following when using insect repellents:

  • Apply repellents only to exposed skin and/or clothing (as directed on the product label). Do not apply repellents under your clothing.
  • Never use repellents over cuts, wounds or irritated skin.
  • Do not apply to eyes or mouth, and apply sparingly around ears. When using repellent sprays, do not spray directly on your face—spray on your hands first and then apply to your face.
  • Do not allow children to handle or spray the product. When using on children, apply to your own hands first and then put it on the child. Avoid applying repellent to children’s hands because children frequently put their hands in their eyes and mouths.
  • Use just enough repellent to cover exposed skin and/or clothing. Heavy application does not give you better or longer lasting protection.
  • After returning indoors, wash treated skin with soap and water or bathe. This is particularly important when repellents are used repeatedly in a day or on consecutive days.
  • If you (or your child) get a rash or other reaction from a repellent, stop using the repellent, wash the repellent off with mild soap and water, and call a local poison control center for further guidance. If you go to a doctor, it might be helpful to take the repellent with you.

Can insect repellents be used on children?

Yes. Most products can be used on children. Products containing oil of lemon eucalyptus should not to be used on children under the age of three years. EPA does not recommend any additional precautions for using registered repellents on children other than those listed above.

Can insect repellents be used by pregnant or nursing women?

Yes. EPA does not recommend any additional precautions for repellent use by pregnant or nursing women.

Can I use an insect repellent and a product containing sunscreen at the same time?

Yes. People can, and should, use both a sunscreen and an insect repellent when they are outdoors. Follow the instructions on the package for proper application of each product. In general, the recommendation is to apply sunscreen first, followed by repellent.

Should I use combination sunscreen/insect repellent products?

It is not recommended to use a single product that combines insect repellent containing DEET and sunscreen. Repellent usually does not need to be reapplied as often as sunscreen. There are not specific recommendations for products that combine other active ingredients and sunscreen. Always follow the instructions on the label of whatever product you are using.

What is permethrin?

Permethrin is a repellent and insecticide. Certain products containing permethrin are recommended for use on clothing, shoes, bed nets, and camping gear. Permethrin-treated products repel and kill ticks, mosquitoes, and other arthropods. These products continue to repel and kill insects after several washings. Permethrin should be reapplied following the label instructions.

FacebooktwitterpinterestyoutubetumblrFacebooktwitterpinterestyoutubetumblr
Ad