West Nile virus is primarily transmitted to humans via mosquito bites; it also affects birds and mammals like horses.e60dc2a1-f33c-4a05-9b50-8e3e8e597629a3e81172-4c73-478e-a067-5a23433ab771 The virus is the leading cause of mosquito-transmitted disease in the United States,e60dc2a1-f33c-4a05-9b50-8e3e8e597629ce42fc21-9333-42dc-9833-03b42243a262 and around 80 percent of people infected with the disease do not experience any symptoms.e60dc2a1-f33c-4a05-9b50-8e3e8e597629e1274cca-56bb-4cee-90f0-3f5a5acbaad0 In about 20 percent of infected people, West Nile virus evolves into a febrile illness (sometimes called West Nile fever), with symptoms including fever, headache, body aches, vomiting, diarrhea, and rash. In rarer cases (about 1 in 150 infected people), West Nile virus can lead to severe and potentially fatal neurological diseases like encephalitis or meningitis. Elderly and immunocompromised people are most at risk for severe disease.e60dc2a1-f33c-4a05-9b50-8e3e8e597629e1274cca-56bb-4cee-90f0-3f5a5acbaad0 There is no vaccine or medicine to treat West Nile virus in humans. The best way to prevent infection is to protect yourself against mosquito bites. Treatment for symptomatic West Nile virus typically involves hospital care.e60dc2a1-f33c-4a05-9b50-8e3e8e597629e1274cca-56bb-4cee-90f0-3f5a5acbaad0
Types of West Nile Virus Types The 1 in 5 people who develop symptoms from West Nile virus experience one of two types: febrile illness and, less commonly, severe neurological illness that can take multiple forms.e60dc2a1-f33c-4a05-9b50-8e3e8e59762906ce877a-1936-4701-8781-5dfc59426b9b
Signs and Symptoms of West Nile Virus Symptoms The symptoms of West Nile virus depend on the form the disease takes when it occurs. Those with febrile illness may experience the following symptoms in addition to fever: Headache Body aches Joint pain Vomiting Diarrhea Rash Additionally, people with febrile illness may experience fatigue or weakness for an extended period — up to weeks or even months — following recovery.
Those who develop neurological disease, which takes the form of brain inflammation (encephalitis) and inflammation of the membranes surrounding the brain and spinal cord ( meningitis ), among others — may experience the following symptoms: High fever Headache Stiffness in the neck Stupor Disorientation Convulsions Tremors Muscle weakness Loss of vision Numbness Paralysis Comae60dc2a1-f33c-4a05-9b50-8e3e8e597629b5ff2591-67ef-4f8a-b556-ddf5e5ae5a3f
Causes and Risk Factors of West Nile Virus Causes In the vast majority of cases, West Nile virus is caused by bites from mosquitos that picked up the virus by feeding on infected birds.e60dc2a1-f33c-4a05-9b50-8e3e8e59762928cc15b9-8ced-48b3-a333-5e319083a5fb In very rare instances, the virus is spread through exposure in a lab, blood transfusions, organ transplants, or from mother to infant via the placenta or breastfeeding. It is not spread through coughing, sneezing, or touching infected people or animals, and you can’t get it from eating infected animals.e60dc2a1-f33c-4a05-9b50-8e3e8e59762929be7ac0-66a4-4bea-bdb8-48d7fa2fe01f Anyone can be bitten by a mosquito and infected, but some people have factors that increase their risk of severe illness. These include: Age 60 or older Organ transplant recipient Cancer Diabetes High blood pressure Kidney disease e60dc2a1-f33c-4a05-9b50-8e3e8e5976295dceb398-6fe5-4227-8b69-00497e9c9fe1
How Is West Nile Virus Diagnosed? Diagnosis A healthcare provider may diagnose West Nile virus on the basis of a person’s signs, symptoms, and history of possible exposure to infected mosquitos.e60dc2a1-f33c-4a05-9b50-8e3e8e597629a89130d2-d05b-4af1-9bd9-a76c000a1a59 The provider will also perform a blood test and in some cases a lumbar puncture , sometimes called a spinal tap.e60dc2a1-f33c-4a05-9b50-8e3e8e597629d70e3bf2-a7bf-43b0-88a6-4f4a20c56fe7
Treatment and Medication Options for West Nile Virus Treatment There are no vaccines, medicines, or other specific treatments for West Nile virus in humans. In generally healthy people with mild febrile illness, rest, fluids, and over-the-counter medications may be enough to relieve symptoms until the infection runs its course.e60dc2a1-f33c-4a05-9b50-8e3e8e597629cdc61d1a-95b6-485b-b89e-89cb078dee0c Treatment in more severe cases typically involves a hospital stay and supportive therapies, such as: Intravenous fluids Breathing support such as a ventilator Monitoring and prevention of secondary infections, such as pneumonia Nursing caree60dc2a1-f33c-4a05-9b50-8e3e8e59762915531053-a21f-498d-b064-ea450612883e
Prevention of West Nile Virus Prevention There are no medical options to prevent infection, but you can protect yourself by taking precautions against mosquito bites . Recommendations include: Insect repellent Long-sleeved, loose-fitting clothing Treat clothing and outdoor gear with permethrin, an insecticide that kills or repels mosquitos Screens and other devices for preventing exposure to mosquitoes in indoor and outdoor spacese60dc2a1-f33c-4a05-9b50-8e3e8e597629b26668da-ccc7-4a9d-9247-c37fe7b41ae7
How Long Does West Nile Virus Last? Prognosis and Outlook Febrile illness from West Nile virus typically lasts a few weeks, though weakness and fatigue can continue for weeks or months afterward. Symptoms such as paralysis, motor impairments, hearing loss, and other neurological conditions may last permanently in more serious cases. West Nile virus is fatal in about 1 in 1,500 people who experience neurological symptoms.e60dc2a1-f33c-4a05-9b50-8e3e8e59762965786aad-ed7b-4c11-9fad-a6c2b838fb11
Complications of West Nile Virus Complications People with febrile illness may experience fatigue or weakness for weeks or months after initial onset. Possible long-term effects of a neurological infection include: Memory loss Hearing loss Gait disorders or difficulty walking Weakness Abnormal reflexes Depressione60dc2a1-f33c-4a05-9b50-8e3e8e59762945edd154-7ddf-4b63-9a78-345b905ee85e
Research and Statistics: How Many People Get West Nile Virus? Research and Statistics There were 1,466 total human cases of West Nile virus illness in the United States in 2024.e60dc2a1-f33c-4a05-9b50-8e3e8e597629e4e21423-1d0a-4393-aeff-8e1783d38b39 In the past 10 years, the number of cases in the country has varied from as low as 731 in 2020 to as high as 2,911 in 2021. The states with the highest number of reported cases between 1999 and 2023 are California, Colorado, Texas, Nebraska, and Arizona.e60dc2a1-f33c-4a05-9b50-8e3e8e59762944a247a8-554c-44a9-8dd4-7c705e27d93d
The Takeaway Four out of five people infected with West Nile virus never experience any symptoms. The best way to prevent infection is to protect yourself against mosquito bites. Most cases of the virus are febrile, with flu-like symptoms. Neurological illness from the West Nile virus is rare but may cause permanent side effects or be fatal in extremely rare cases.
Resources We Trust Cleveland Clinic: West Nile Virus Mayo Clinic Health System: West Nile virus: What you need to know Centers for Disease Control and Prevention: Preventing West Nile Johns Hopkins Medicine: West Nile Virus MedlinePlus: West Nile Virus
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