For most people who get sick from West Nile virus, symptoms last 3 to 6 days, though they can stretch to a month in some cases. The timeline varies dramatically depending on severity: the majority of infected people never feel sick at all, a smaller group gets a short-lived fever, and a rare but serious subset develops brain or spinal cord complications that can take months or years to recover from, if they recover fully.
When Symptoms First Appear
After being bitten by an infected mosquito, symptoms typically show up within 2 to 6 days. People with weakened immune systems may take longer to develop signs of illness. About 80% of people infected with West Nile virus never develop symptoms at all, meaning they carry and clear the virus without knowing it.
Duration of Mild Illness
Roughly 1 in 5 infected people develop what’s known as West Nile fever: a flu-like illness with fever, headache, body aches, fatigue, and sometimes nausea or diarrhea. These symptoms usually resolve within 3 to 6 days but can persist for up to a month in some cases.
About half of people with an acute infection develop a rash, typically on the trunk, back, or arms. The rash usually lasts less than seven days and may be itchy. Even after the fever breaks and the rash fades, lingering fatigue, general weakness, and a washed-out feeling can hang around for weeks or months. This post-viral fatigue is one of the most common complaints and often outlasts every other symptom.
How Long the Virus Stays in Your Blood
The virus itself circulates in the bloodstream for a relatively short window. It’s typically detectable in blood plasma from 2 to 18 days after infection and up to 5 days after symptoms begin, though prolonged circulation lasting up to 35 days after symptom onset has been documented in some patients. Your immune system produces antibodies that are usually detectable 3 to 8 days after you start feeling sick, and these antibodies typically persist for 30 to 90 days, sometimes longer.
Recovery From Severe Cases
About 1 in 150 infected people develop neuroinvasive disease, meaning the virus crosses into the brain or spinal cord, causing meningitis (inflammation of the membranes around the brain), encephalitis (inflammation of the brain itself), or acute flaccid myelitis (a type of paralysis affecting the limbs). These are the cases where the timeline stretches from weeks into months or longer.
People who develop meningitis generally recover completely, but the acute illness itself can be intense, requiring hospitalization. Those who develop encephalitis or paralysis often face a much longer road. Recovery from severe illness takes several weeks to months, and some effects can be permanent. Between 30% and 40% of hospitalized patients are discharged to long-term care or rehabilitation facilities rather than going home. More than half of hospitalized patients still report ongoing symptoms over a year after their illness, including muscle weakness, difficulty concentrating, memory problems, and persistent fatigue.
The fatality rate for neuroinvasive cases is about 9% overall, but age matters enormously. For patients under 50, the fatality rate is around 2%. It rises to 6% for those aged 50 to 69 and jumps to 21% for people 70 and older.
Long-Term Effects After Recovery
Even people who had only moderate illness sometimes report a slow return to normal. The most commonly reported lingering problems are fatigue, muscle weakness, and cognitive difficulties like trouble with memory or concentration. For mild cases, these typically fade within a few weeks to a couple of months.
For severe cases, the picture is different. Patients who had encephalitis or paralysis often have residual neurological deficits that persist indefinitely. Physical rehabilitation can improve function, but some degree of weakness or cognitive change may be permanent. The physical, cognitive, and functional challenges after severe West Nile infection resemble the long recovery arc seen with other forms of viral brain inflammation, where the initial illness resolves but the damage it caused takes much longer to heal, or doesn’t fully resolve.
What Determines How Long It Lasts
Your age and immune function are the two biggest factors. Older adults, particularly those over 60, are far more likely to develop severe illness and face longer recovery times. People with conditions that suppress the immune system, such as organ transplant recipients or those on certain medications, also tend to have more prolonged and serious courses of illness.
There’s no antiviral treatment that shortens the duration of West Nile virus. Care is supportive: rest, fluids, and over-the-counter pain relief for mild cases, and hospital-based care including respiratory support and rehabilitation for severe ones. Your body clears the virus on its own. The variable is how much inflammation and damage occurs before it does.