West Nile Virus: The Mosquito Bite That Mostly Isn't, and the Rare One That Is
Last updated September 4, 2026.
West Nile virus is spread by mosquitoes that have fed on infected birds, and it is the commonest mosquito-borne illness in the continental United States, arriving each summer and fall. Here is the statistical spine: about eighty percent of infected people feel nothing at all. Most of the rest get West Nile fever: a few days to two weeks of fever, headache, body aches, sometimes a rash and swollen glands, and then recovery, though fatigue can trail for weeks. Fewer than one percent develop the neuroinvasive disease: meningitis, encephalitis, or a polio-like paralysis, and that small minority is the reason for the rest of this page.
The mild majority
West Nile fever begins two to fourteen days after the bite: fever, headache, body aches, tiredness, sometimes a rash on the trunk and swollen glands. There is no specific medicine and none is needed: rest, fluids, and ordinary fever relief, and the illness passes, though the tiredness and fog can linger for weeks, which is documented and fades. Once you have had West Nile, you are generally immune going forward.
West Nile is silent in most, a fever week in many, and dangerous in under one percent. The emergency line is stiff neck, confusion, tremors, or sudden weakness; the prevention is repellent, sleeves, and no standing water.
Start a free AI doctor consult →The dangerous minority
The neuroinvasive disease announces differently: high fever with severe headache, neck stiffness, confusion, tremors, seizures, or sudden weakness, sometimes a flaccid paralysis that looks like a stroke. Anyone over sixty, and anyone with immunity weakened by transplant medicines, cancer treatment, or similar, carries the higher risk for this form. There is no antiviral; treatment is hospital support while the inflammation runs its course, and recovery from the severe form is slow and can be incomplete, with lasting weakness or fatigue. New confusion, stiff neck, or sudden weakness during a summer fever is an emergency, not a wait-and-see.
Prevention is the whole strategy
No vaccine exists for people, so the defense is the bite itself: repellent with DEET or picaridin on exposed skin, long sleeves and trousers at dawn and dusk when the mosquitoes work, window screens intact, and standing water emptied weekly, because birdbaths, clogged gutters, and flowerpot saucers are mosquito nurseries. Community spraying happens where surveillance warrants. The summer the headlines arrive, the rules are boring and they work: the people who avoid the bites avoid the disease, and for everyone bitten anyway, the odds remain overwhelmingly on the mild side.
- Summer fever with stiff neck, confusion, or sudden weakness is an emergency. Especially over sixty or on immunity-suppressing medicine. That combination skips the waiting room and goes to the emergency department.
- The lingering tiredness is real. After the mild form, weeks of fatigue and fog are the documented course, not imagination. They fade; plan for a slower return, not a broken body.
- Repellent, sleeves, and empty water. DEET or picaridin, cover up at dawn and dusk, and dump standing water weekly. No vaccine exists, so the bite is the battlefield, and it is a winnable one.
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Common questions
What are the chances a bite gives me West Nile?
Low, and lower still that you would know: about eighty percent of infected people have no symptoms at all. Most of the rest get a self-limited fever illness. Fewer than one percent develop the neurologic form, and age over sixty plus weakened immunity are the main risk factors for that.
What does the mild form feel like?
Fever, headache, body aches, and tiredness starting two to fourteen days after the bite, sometimes with a trunk rash and swollen glands, lasting days to two weeks. Fatigue and fog can trail for weeks afterward, which is documented and fades.
When is it an emergency?
High fever with severe headache and a stiff neck you cannot bend, confusion or unusual drowsiness, tremors, a seizure, or sudden weakness, especially one-sided. Any of those, especially over sixty or on immunity-suppressing medicine, means the emergency department immediately.
Is there a treatment or vaccine?
No specific antiviral and no human vaccine: the mild form is managed with rest, fluids, and fever relief, and the severe form with hospital support while the inflammation runs its course. Prevention, repellent and covering up, is the whole strategy.
Can I get it again?
Once you have had West Nile, you are generally immune going forward. The immunity is one of the few bright sides of a miserable fortnight.
How do I protect myself for the rest of the season?
Repellent with DEET or picaridin on exposed skin, long sleeves and trousers at dawn and dusk, intact window screens, and standing water emptied weekly, birdbaths, gutters, flowerpot saucers. The rules are boring and they are the entire defense, and they work.