St. Louis County Confirms 1st West Nile Detection in 2026 Mosquitoes

Q: Eighty percent of West Nile cases are asymptomatic, so what determines if a mosquito bite is harmless or fatal?

What makes a West Nile infection harmless or dangerous is less the bite itself than what happens after infection: whether the immune system clears the virus quickly or the virus reaches the brain and spinal cord. In about 80% of infections, people never feel sick because their immune response controls the virus early. About 20% develop West Nile fever, a usually self-limited illness with fever, headache, body aches, rash, vomiting or diarrhea. Fewer than 1% develop neuroinvasive disease, when the virus crosses into the central nervous system and causes meningitis, encephalitis or acute flaccid paralysis. That is the form linked to deaths; roughly 1 in 10 severe neuroinvasive cases is fatal. Who gets severely ill is strongly shaped by host risk factors. Age is one of the clearest: risk rises sharply after 50 and especially in older adults. People with weakened immune systems or chronic conditions such as cancer, diabetes, hypertension or kidney disease are also more vulnerable. Those conditions can make it harder to contain the virus before it spreads. Scientists do not fully predict, person by person, who will worsen, but the main drivers are clear: viral spread to the nervous system and the patient’s age and health status. Because there is no vaccine or specific antiviral treatment, public health officials stress prevention and early attention to warning signs such as high fever, stiff neck, confusion, seizures or sudden weakness.

3 articles · Updated · West Newsmagazine · Jul 20

July 9 samples from a Richmond Heights surveillance site produced St. Louis County’s first confirmed West Nile virus detection in mosquitoes this season.
West Nile spreads through mosquito bites, and while many infections cause no illness, about 1 in 5 people develop symptoms including fever, headache, body aches, vomiting, diarrhea or rash.
Rare cases can progress to potentially fatal neurological illness, with residents over 50, immunocompromised people and those with chronic conditions facing higher risk.
The county health department said there is no vaccine or antiviral treatment and urged residents to use EPA-registered repellent, wear protective clothing and remove standing water to curb mosquito breeding.