Over the weekend, helicopters sprayed a 20-square-mile area of northern New York City, after health officials confirmed five cases of Saint Louis encephalitis and investigated dozens more.
"The symptoms we're most concerned about -- the actual encephalitis -- are fever, headache, confusion, and then neurologic abnormalities like muscle weakness or seizures or tremors," said Marcelle Layton of the New York City Department of Health.
Health officials are surprised that it occurred in New York, which hasn't seen this strain in 25 years. More shocking, the death toll: so far two people here. That's the annual average for the entire nation. And there's no specific treatment.
"Most people will get better on their own just with time and supportive care," said Layton. "Unfortunately, others, about 10 per cent of cases, especially the elderly, may die."
There are several types of mosquitoes that carry St. Louis encephalitis. The female culex pipiens is believed to be the culprit. It contracts the disease from infected birds and transmits it to people.
Residents are being warned to cover their arms and legs -- and use insect repellant on exposed skin.
But with hot weather and the knowledge that the mosquito usually strikes after dusk, most dressed for the heat and seemed to ignore the threat.
Experts warn that the threat of encephalitis will continue until shorter days and cooler temperatures change the mosquitoes' dietary habits. They'll switch from feeding off humans to eating plant pollen in preparation for winter hibernation.