Keystone Infectious Disease’s Medical Director, Dr. Raghavendra Tirupathi, and medical students studying under him, Drs. Hema Manvi Koneru, Divya Joshi and Sumanth Gundraju, explain the dangers of West Nile Virus in today’s Take Care article.
What is West Nile Virus, and how does it affect people?
West Nile Virus is an infection that is spread to humans by the bite of infected mosquitoes. The virus lives in nature through a cycle between birds and mosquitoes, and humans typically become infected when a mosquito feeds on an infected bird and then bites a person. The illness does not spread through contact such as touching, hugging or being close to someone who has it. However, a pregnant woman can pass it to their baby before birth, and it can also be passed through breast milk. In very rare situations, it can spread through blood transfusions or organ transplants. To keep people safe, all donated blood in the United States is tested for the virus, and anyone who has had the illness should not donate blood or bone marrow for 120 days following infection.
This virus is the most common disease spread by mosquitoes in the continental United States. According to the CDC, as of August 2025, 219 cases in 29 states had been reported in the US, including 119 severe cases that have affected the brain or nervous system.
What are the symptoms?
Most people do not develop symptoms from West Nile Virus. About one in five experience fever along with other symptoms such as headache, body or joint pain, vomiting, diarrhea or skin rash. These symptoms can last from a few days to several weeks, and in some cases, persistent fatigue and weakness may linger for much longer. A small number of people, roughly one in 150, develop a serious illness that affects the brain and nervous system. This can include high fever, severe headache, stiff neck, confusion, shaking, seizures, muscle weakness, vision problems, numbness, paralysis, coma and, in rare cases, death.
How is it diagnosed?
If you think you or a loved one might have West Nile Virus, contact your healthcare provider. Diagnosis is usually based on symptoms and laboratory tests, which your provider may order to confirm West Nile Virus or to rule out other infections with similar symptoms. Labs may include bloodwork or cerebrospinal fluid antibody tests to look for specific proteins your body makes in response to the virus. These proteins are typically detectable a few days after symptoms start.
In some cases, like when people have weakened immune systems, other testing methods may be used. Most people experience mild illnesses, but those with weakened immune systems or severe symptoms may need closer monitoring.
How is it treated?
There is no specific medicine to cure West Nile virus. Antibiotics do not work because it is a viral infection. Treatment focuses on symptom relief and supportive care such as rest and fluids to help your body recover and over-the-counter pain relievers for fever, headache or body aches. Hospital care may be needed for severe cases affecting the brain or nervous system. In a hospital setting patients can be monitored for complications such as seizures or breathing difficulty and given necessary support.
Some treatments, such as immune therapies, interferon, ribavirin or corticosteroids have been studied, but none has been proven to reliably improve outcomes.
Do you have immunity after infection?
Most people who recover from West Nile Virus develop long-lasting immunity, which makes it unlikely to get infected again. People with weakened immune systems may have less protection and should continue taking precautions.
How can you reduce risk?
Despite promising advancements in research and clinical trials for human vaccines, no FDA-approved options are currently available. Therefore, the best way to reduce risk is to prevent mosquito bites.
Mosquitoes are most active during the summer months, but they remain a threat well into the fall season, especially at dusk and dawn. Protect yourself when spending time outdoors by wearing long sleeves and loose-fitting pants and using insect repellents containing DEET or picaridin. The Environmental Protection Agency maintains lists of approved insect repellents that can be applied directly to the skin. Permethrin is a repellent that can be used to treat clothing and gear, including tents. Empty standing water at least once per week. On items such as rain barrels, apply a screen to the opening to restrict mosquito access. Screens should also be fitted to windows and doors that are left open.
Dead birds can transmit infection as well. If you find one, don’t handle it with your bare hands and consider reporting it to your state health department. This can help local programs detect West Nile virus in your area.
This article contains general information only and should not be used as a substitute for professional diagnosis, treatment or care by a qualified health care provider.
