West Nile virus

Medical Specialties: Allergy/immunology, Internal medicine

Clinical Definition

West Nile virus is an arthropod-borne flavivirus transmitted by mosquitos. Most infected individuals are asymptomatic, but some develop a mild febrile illness. Though rare, certain West Nile virus may evolve into more serious illnesses, such as West Nile meningoencephalitis.

In Our Own Words

The West Nile virus is an infection spread by mosquitos. Due to relatively mild symptoms, the virus is often undetected and thus, untreated in patients.


Some cases of the virus will cause West Nile fever, producing fever and body aches. In rare instances, the virus will infect the lining of the brain and spinal cord (i.e., meninges) or create inflammation in the brain itself (i.e., viral meningoencephalitis) to produce symptoms such as stiff neck, decreased mental abilities, reduced alertness and tremors.


Less than 1 percent of people who are infected become seriously ill from West Nile virus. Elderly people and those with weak immune systems are more likely to experience severe symptoms. There is currently no vaccine available for West Nile virus; however, the mainstay of prevention involves using insect repellent and subsequently, reducing the risk of mosquito bites.

Relevant Conditions
  • Viral meningoencephalitis
  • West Nile fever
  • West Nile encephalitis
Side Effects
  • Rash
  • Headache
  • Fever
  • Body aches
  • Swollen glands
Share this article
  • Cleveland Clinic. “Understanding the West Nile Virus.” http://my.clevelandclinic.org/disorders/west_nile_virus/hic_understanding_the_west_nile_virus.aspx. Accessed July 2013.
  • University of Maryland Medical Center. “West Nile virus.“ Updated May 2013. http://umm.edu/health/medical/ency/articles/west-nile-virus. Accessed July 2013.
  • Lindsey N., MS, Lehman J., Staples E., MD, et al. “West Nile Virus and Other Arboviral Diseases — United States, 2012.” Morbidity and Mortality Weekly Report (MMWR), Centers for Disease Control and Prevention. 2013; 62(25); pages 513 – 517. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6225a1.htm?s_cid=mm6225a1_w. Accessed July 2013.
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