Table of ContentsView AllTable of ContentsSymptomsCausesDiagnosisTreatmentPrevention
Table of ContentsView All
View All
Table of Contents
Symptoms
Causes
Diagnosis
Treatment
Prevention
This article discusses the symptoms, causes, and diagnosis of West Nile virus, as well as treatment and ways to prevent it.
Verywell / Emily Roberts
West Nile Virus Symptoms
It is estimated that 60% to 80% of people who get infected with the West Nile virus have no signs or symptoms of any disease. Roughly 20% will develop what is called West Nile fever.
Symptoms of West Nile fever may include:
These typical viral symptoms usually improve after a few days and are usually considered to be just a “summer cold.” Most people and their healthcare providers never knew they had a West Nile virus infection.
West Nile fever is a self-limited illness that is indistinguishable from many other viral infections.
Meningitis/Encephalitis
In a small number of infected people—thought to be well under 1%—a serious neurological infection can occur.
People who develop West Nile meningitis or encephalitis may experience:
West Nile meningitis or encephalitis can be fatal, even with comprehensive medical care. Many who recover have lingering neurological symptoms for a year or longer, and some may be left with permanent neurological deficits.
The neurological complications from West Nile virus are more likely in:
What Causes West Nile Virus?
West Nile virus is anRNA virusthat is found all over the world, including Europe, Africa, Asia, Australia, and North and South America. While the virus itself is not new, it was far more localized to Africa and the Middle East until a few decades ago. Scientists first associated it with severe neurological illness only during the 1990s.
The primary hosts for the West Nile virus are birds. Mosquitoes pass the virus from bird to bird, allowing the virus to multiply and spread. When a mosquito carrying the virus bites a person, the virus can enter the bloodstream and cause an infection.
In the United States, West Nile virus was first detected in 1999, with a major outbreak of illness in New York City. It has now been identified in every one of the 48 contiguous states. Up to 3000 cases of neurological infections from West Nile virus have been seen annually in the United States in recent years.
In the northern hemisphere, infections with the West Nile virus are seen from late May or early June through September, when mosquitoes are active. The risk of infection tends to peak in late summer.
How Is West Nile Virus Diagnosed?
Two tests may be used to identify West Nile virus infection:
The PCR and ELISA tests are costly. These tests are usually only performed if a doctor feels it’s imperative to formally diagnose West Nile infection, such as in cases when an individual is seriously ill.
Most people with the infection don’t experience symptoms or only have mild flu-like symptoms that resolve on their own. While those with mild cases might want to officially know if it’s West Nile that is affecting them, a test-confirmed diagnosis won’t affect treatment recommendations.
Symptoms of West Nile Virus
West Nile Virus Treatment
There is no specific therapy for West Nile virus, so treatment is primarily focused on reducing symptoms.Those with typical West Nile fever (the vast majority of whom never learn they are infected with the West Nile virus) generally treat themselves with usual comfort measures—rest, fluid, and pain relievers—and their illnesses resolve in a few days.
West Nile Virus Doctor Discussion GuideGet our printable guide for your next doctor’s appointment to help you ask the right questions.Download PDFEmail AddressSign UpThank you, {{form.email}}, for signing up.There was an error. Please try again.
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People who are hospitalized with a serious illness from West Nile virus are treated to manage the fever and to keep vital signs (pulse, temperature, breathing rate, and blood pressure) stable.
Whileantiviral medicationandintravenous immunoglobulinare often used to treat West Nile infection in hospitalized patients, real evidence that these treatments help with recovery is lacking.
Mortality with serious neurological West Nile infection, even with optimal medical care, has been reported as 4.6% in the United States between 1999 to 2019.
How to Prevent West Nile Virus
Because there are no good treatments for this infection, prevention is very important. Ways to prevent or reduce the risk of infection, include:
Vaccinesagainst West Nile virus are being developed. While vaccines for horses have been licensed for use in the United States, no vaccines for human use have yet entered clinical trials.
Summary
West Nile virus is a mosquito-borne infection that is widespread across the United States and the world. While most people infected with West Nile virus have relatively mild illnesses and recover completely, those who develop neurological infections can become seriously ill and may have a prolonged recovery, as well as a risk of death.
8 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.New York State. Department of Health.West Nile virus - frequently asked questions.Centers for Disease Control and Prevention.Symptoms, diagnosis, & treatment.Sejvar JJ.West Nile virus infection. Scheld WM, Hughes JM, Whitley RJ, eds.Microbiol Spectr. 2016;4(3):4.3.20. doi:10.1128/microbiolspec.ei10-0021-2016Centers for Disease Control and Prevention.Transmission of West Nile virus.World Health Organization.West Nile virus.Centers for Disease Control and Prevention.Treatment and prevention of West Nile virus disease.Ronca SE, Ruff JC, Murray KO.A 20-year historical review of West Nile virus since its initial emergence in North America: Has West Nile virus become a neglected tropical disease?PLoS Negl Trop Dis. 2021 May 6;15(5):e0009190. doi: 10.1371/journal.pntd.0009190National Institute of Allergy and Infectious Diseases.West Nile virus vaccines.Additional ReadingLoeb M, Hanna S, Nicolle L, et al.Prognosis after West Nile virus infection.Ann Intern Med. 2008; 149:232.Murray KO, Garcia MN, Rahbar MH, et al.Survival analysis, long-term outcomes, and percentage of recovery up to 8 years post-infection among the Houston West Nile virus cohort.PLoS One. 2014; 9:E102953.O’Leary DR, Marfin AA, Montgomery SP, et al.The epidemic of West Nile virus in the United States, 2002.Vector Borne Zoonotic Dis.2004; 4:61.
8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.New York State. Department of Health.West Nile virus - frequently asked questions.Centers for Disease Control and Prevention.Symptoms, diagnosis, & treatment.Sejvar JJ.West Nile virus infection. Scheld WM, Hughes JM, Whitley RJ, eds.Microbiol Spectr. 2016;4(3):4.3.20. doi:10.1128/microbiolspec.ei10-0021-2016Centers for Disease Control and Prevention.Transmission of West Nile virus.World Health Organization.West Nile virus.Centers for Disease Control and Prevention.Treatment and prevention of West Nile virus disease.Ronca SE, Ruff JC, Murray KO.A 20-year historical review of West Nile virus since its initial emergence in North America: Has West Nile virus become a neglected tropical disease?PLoS Negl Trop Dis. 2021 May 6;15(5):e0009190. doi: 10.1371/journal.pntd.0009190National Institute of Allergy and Infectious Diseases.West Nile virus vaccines.Additional ReadingLoeb M, Hanna S, Nicolle L, et al.Prognosis after West Nile virus infection.Ann Intern Med. 2008; 149:232.Murray KO, Garcia MN, Rahbar MH, et al.Survival analysis, long-term outcomes, and percentage of recovery up to 8 years post-infection among the Houston West Nile virus cohort.PLoS One. 2014; 9:E102953.O’Leary DR, Marfin AA, Montgomery SP, et al.The epidemic of West Nile virus in the United States, 2002.Vector Borne Zoonotic Dis.2004; 4:61.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
New York State. Department of Health.West Nile virus - frequently asked questions.Centers for Disease Control and Prevention.Symptoms, diagnosis, & treatment.Sejvar JJ.West Nile virus infection. Scheld WM, Hughes JM, Whitley RJ, eds.Microbiol Spectr. 2016;4(3):4.3.20. doi:10.1128/microbiolspec.ei10-0021-2016Centers for Disease Control and Prevention.Transmission of West Nile virus.World Health Organization.West Nile virus.Centers for Disease Control and Prevention.Treatment and prevention of West Nile virus disease.Ronca SE, Ruff JC, Murray KO.A 20-year historical review of West Nile virus since its initial emergence in North America: Has West Nile virus become a neglected tropical disease?PLoS Negl Trop Dis. 2021 May 6;15(5):e0009190. doi: 10.1371/journal.pntd.0009190National Institute of Allergy and Infectious Diseases.West Nile virus vaccines.
New York State. Department of Health.West Nile virus - frequently asked questions.
Centers for Disease Control and Prevention.Symptoms, diagnosis, & treatment.
Sejvar JJ.West Nile virus infection. Scheld WM, Hughes JM, Whitley RJ, eds.Microbiol Spectr. 2016;4(3):4.3.20. doi:10.1128/microbiolspec.ei10-0021-2016
Centers for Disease Control and Prevention.Transmission of West Nile virus.
World Health Organization.West Nile virus.
Centers for Disease Control and Prevention.Treatment and prevention of West Nile virus disease.
Ronca SE, Ruff JC, Murray KO.A 20-year historical review of West Nile virus since its initial emergence in North America: Has West Nile virus become a neglected tropical disease?PLoS Negl Trop Dis. 2021 May 6;15(5):e0009190. doi: 10.1371/journal.pntd.0009190
National Institute of Allergy and Infectious Diseases.West Nile virus vaccines.
Loeb M, Hanna S, Nicolle L, et al.Prognosis after West Nile virus infection.Ann Intern Med. 2008; 149:232.Murray KO, Garcia MN, Rahbar MH, et al.Survival analysis, long-term outcomes, and percentage of recovery up to 8 years post-infection among the Houston West Nile virus cohort.PLoS One. 2014; 9:E102953.O’Leary DR, Marfin AA, Montgomery SP, et al.The epidemic of West Nile virus in the United States, 2002.Vector Borne Zoonotic Dis.2004; 4:61.
Loeb M, Hanna S, Nicolle L, et al.Prognosis after West Nile virus infection.Ann Intern Med. 2008; 149:232.
Murray KO, Garcia MN, Rahbar MH, et al.Survival analysis, long-term outcomes, and percentage of recovery up to 8 years post-infection among the Houston West Nile virus cohort.PLoS One. 2014; 9:E102953.
O’Leary DR, Marfin AA, Montgomery SP, et al.The epidemic of West Nile virus in the United States, 2002.Vector Borne Zoonotic Dis.2004; 4:61.
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