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What Is West Nile Virus Infection (West Nile Fever)?

Overview

Highlights

  1. If you have West Nile virus, you will typically show the first virus symptoms within three to 14 days of being bitten by the infecting mosquito.
  2. Around 70 to 80 percent of people who are infected won’t show any symptoms.
  3. Mosquito bites are most common in late August to early September.

A mosquito bite can turn into something much more severe if it infects you with the West Nile virus (sometimes called WNV). Mosquitoes transmit this virus by biting an infected bird and then biting a person. Not all people with infected mosquito bites get the disease, however.

WNV can be severe for people older than 60 years and people with weakened immune systems. If diagnosed and treated quickly, the outlook for West Nile virus recovery is good.

Symptoms

Symptoms

If you have West Nile virus, you will typically show the first virus symptoms within three to 14 days of being bitten. West Nile virus symptoms vary in severity. Severe symptoms can include:

  • fever
  • confusion
  • convulsions
  • muscle weakness
  • vision loss
  • numbness
  • paralysis
  • coma

A severe infection can last for several weeks. In rare cases, a severe infection can cause permanent brain damage.

A mild infection doesn’t usually last as long. Mild forms of West Nile virus may be confused with the flu. Symptoms include:

  • fever
  • headache
  • body aches
  • nausea
  • vomiting
  • swollen lymph glands
  • rash on your chest, stomach, or back

Causes

Causes

Infected mosquitoes usually spread the West Nile virus. The mosquito first bites an infected bird and then bites a human or another animal. In rare cases, blood transfusions, organ transplants, breastfeeding, or pregnancy can transfer the virus and spread the illness. West Nile virus can’t be spread by kissing or touching another person.

Risk factors

Risk Factors

Anyone bitten by an infected mosquito can get West Nile virus. However, less than one percent of people who are bitten develop severe or life-threatening symptoms.

Age is one of the most significant risk factors for developing severe symptoms from a West Nile infection. The older you are (especially if you’re over 60), the more likely you are to face harsher symptoms.

Medical conditions that increase your risk of severe symptoms include:

  • kidney conditions
  • diabetes
  • hypertension
  • cancer
  • impaired immune system

Diagnosing the infection

Diagnosis

In most cases, your doctor can diagnose West Nile virus with a simple blood test. This can determine whether you have genetic material or antibodies in your blood associated with West Nile virus.

If your symptoms are severe and brain-related, your physician may order a lumbar puncture. Also known as a spinal tap, this test involves inserting a needle into your spine to extract fluid. West Nile virus can elevate the white blood cell count in the fluid, which indicates an infection. MRI and other imaging scans can also help detect inflammation and brain swelling.

Image of skin affected by West Nile virus

West Nile Virus

Treatment

Treatment

Because it’s a viral condition, West Nile virus doesn’t have a cure. But you can take over-the-counter pain relievers, such as ibuprofen or aspirin, to relieve symptoms of West Nile virus such as muscle aches and headaches.

If you experience brain swelling or other severe symptoms, your doctor may give you intravenous fluids and medications to lower the risk of infections.

Research is currently being done on interferon therapy for West Nile virus. Interferon therapy is aimed at using substances produced by your immune system to treat encephalitis in people infected by West Nile virus. The research isn’t conclusive about the use of these therapies for encephalitis, but studies are promising.

Other potential treatments being researched for West Nile-related encephalitis include:

  • polyclonal immunoglobulin intravenous (IGIV)
  • WNV recombinant humanized monoclonal antibody (MGAWN1)
  • corticosteroids

Your doctor may discuss one or more of these treatments with you if you have encephalitis and your symptoms are severe or life-threatening.

Facts and statistics

Results/Exams

West Nile virus is most commonly spread during the summer, especially between June and September. Around 70 to 80 percent of people who are infected won’t show any symptoms.

Around 20 percent of infected people will show some fever symptoms, such as headaches, vomiting, and diarrhea. These symptoms usually pass quickly. Some symptoms, such as fatigue, can continue for up to several months after the initial infection.

Fewer than one percent of people who get West Nile virus infections develop severe symptoms or neurological conditions such as meningitis or encephalitis. Of these cases, fewer than 10 percent are fatal.

Preventing infection

Prevention

Every mosquito bite increases your risk of infection. These steps can help you prevent West Nile virus each time you are outdoors:

  • Keep your skin covered with long-sleeve shirts, pants, and socks.
  • Wear an insect repellent.
  • Eliminate any standing water around your home (mosquitos are attracted to standing water).
  • Make sure your home’s windows and doors have screens to stop mosquitos from entering.
  • Use mosquito netting, especially around playpens or strollers, to protect you and your children from mosquito bites.

Mosquito bites are most common in late August to early September. Your risk is reduced during colder months because mosquitoes can’t survive in cold temperatures.

Report any dead birds you see to your local health agency. Don’t touch or handle these birds. Dead birds can easily pass the West Nile virus on to mosquitos, which can pass it to humans even with a single bite. If any signs of the virus are found in the area around the bird, the health agency will likely increase pest control activity or pesticide use. These actions can prevent the spread of the virus before it’s passed on to humans.

Outlook

Outlook

Though a vaccine exists to protect horses against West Nile virus, there is no vaccine for people.

Supportive care during a West Nile virus infection, especially a severe one, is important to survival. Seek treatment if you notice any of the symptoms described above, especially if you know you’ve recently been bitten by a mosquito or visited a place with many mosquitos.

You’re likely to get better quickly and make a full recovery from a West Nile virus infection. But immediate and consistent treatment is the best way to make sure that your symptoms remain mild. This is especially true if you have certain risk factors, such as old age or certain medical conditions.

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