Around 4 in 5 people infected with West Nile virus never develop symptoms at all. Around 1 in 5 get a mild, flu-like illness with fever, headache, body aches, and sometimes a rash. Fewer than 1 in 100 develop a serious neurological illness that requires medical care.
West Nile virus can be a serious illness, and it’s reasonable to fear it to some extent. Most of the time, however, it’s either asymptomatic or mild. Here’s what you need to know.
Most people who catch West Nile virus never know. As many as 80% of people who are infected never feel sick and never know they had it. Their immune system quietly handles it.
About 20% of people who are infected with West Nile virus develop West Nile fever. Symptoms show up a few days to two weeks after the bite and can include fever, headache, body and muscle aches, joint pain, nausea or vomiting, and occasionally a skin rash. Most people recover on their own, though the fatigue and weakness can linger for weeks.
There is a small group of people, fewer than 1 in 100, who develop serious West Nile virus disease. In rare cases, people can develop neuroinvasive disease, where the virus affects the brain and nervous system, causing encephalitis or meningitis. Warning signs include high fever, a stiff neck, severe headache, confusion or disorientation, tremors, muscle weakness, seizures, and in some cases paralysis. This form requires immediate medical care and hospitalization. The most likely groups of people to face the most serious version of West Nile virus are adults over 60 and those with weakened immune systems or certain chronic conditions.
There's no specific antiviral treatment or vaccine for West Nile virus. When care is provided, it’s focused on managing symptoms. This, along with the fact that the virus has turned up in local mosquito populations in recent years, is why health departments monitor for it through the summer. Anyone experiencing high fever with confusion, stiff neck, or weakness after mosquito exposure should seek medical care immediately.
