Symptoms of West Nile Virus

Mosquito-borne disease now endemic in the United States

Asian tiger mosquito (Aedes albopictus) feeding on human blood.

West Nile fever is a mosquito-borne infection of the West Nile virus. While the disease was long constrained in Africa, southeast Asia, the Middle East, and southern Europe, it has since made the leap to the Western hemisphere. It is now endemic in the United States and has been gradually spreading to Central and South America.

Unsurprisingly, West Nile fever is most commonly seen in temperate, tropical climates where mosquitoes thrive.

The people at greatest risk of severe disease are the elderly, the very young, and people with compromised immune systems (such as those with advanced HIV infection or recent organ donor recipients).

In 2012, the U.S. experienced one of its worst outbreaks in which 286 people died, mostly in Texas. There is currently no vaccine for the West Nile fever.

Common Symptoms of West Nile Fever

The incubation period for West Nile fever—the time between infection and symptoms— is usually between two and 14 days. Approximately 80 percent of people exposed to the virus will have no symptoms. Those who do will generally experience them between three and six days.

The most common symptoms include:

  • Fever
  • Headache
  • Muscle aches (myalgia)
  • Joint pain (arthralgia)
  • Excessive sweating
  • Nausea
  • Vomiting
  • Diarrhea
  • Swollen lymph glands (lymphadenopathy)
  • Skin rash, characterized by small red bumps

The symptoms are usually mild and tend to last for a few days or weeks.

Symptoms of West Nile Neuroinvasive Disease

In rare cases, people infected with the West Nile virus may experience severe disease neuroinvasive disease. These include encephalitis (inflammation of the brain) or meningitis (inflammation of the protective membrane around the brain and spinal cord called the meninges).

When it affects the spinal cord itself, it is referred to as West Nile poliomyelitis. Symptoms of West Nile neuroinvasive disease may include:

  • Severe headache
  • High fever
  • Neck stiffness
  • Stupor or disorientation
  • Muscle weakness
  • Tremors
  • Numbness
  • Seizures
  • Vision loss
  • Paralysis (most typically with poliomyelitis)

Preventing West Nile Fever

West Nile fever is transmitted through mosquito bites and cannot be spread through casual contact with others. As such, prevention efforts should be focused on avoiding bites and minimizing infestations, particularly from mid-August to October when the brunt of infections occur.

Prevention efforts should include the following:

  • Use an insect repellent containing a minimum of 30 percent DEET for adults and no more than 30 percent for children over two. Insect repellent is not recommended children younger than two.
  • In areas where mosquitoes are prevalent, consider using mosquito netting over your bed. While there are some netting products with built-in repellent, you should opt for plain netting for smaller children (if only to avoid the risk of them sucking on the fabric).
  • Empty any standing water around your home where mosquitoes can breed.
  • Wear protective clothing in areas where mosquitoes are prevalent. Tuck your pants into your socks, button your sleeves and cover your head with a hat. Apply insect repellent to your clothing. Do not apply insect repellent under your clothing.


    Centers for Disease Control and Prevention. "West Nile virus." Atlanta, Georgia; updated August 2, 2017.

    Murray, K.; Ruktanonchai, D.; Hesalroad, D. et al. "West Nile virus, Texas, USA, 2012." Emerging Infectious Diseases. 2013; 1(11):1836-8.