First, crows began dying. ŠAMNH
 
A Medical Detective Story
As the summer of 1999 progressed, the people of New York City gradually became aware that something strange was afoot. First, crows began dying. Then some elderly Queens residents got very sick. Was there a connection? What could it be?

June 1999
Queens residents began reporting that crows with no visible wounds were hobbling around, disoriented and dying.

July
Dead crows were found in a neighboring borough, the Bronx.

August 23
Dr. Deborah Asnis, an infectious disease specialist at Flushing Hospital in Queens, called the city's health department with news that 3 elderly patients had symptoms of what looked like a neurological illness: fever, weakness, and confusion. Samples of blood and spinal fluid went to the state Department of Health and Atlanta's Center for Disease Control (CDC) with the warning that something was breaking out in New York City.

August 28
The cluster of sick people reaches four. Family members were interviewed to find out where the patients had traveled and what they'd been eating. The only constant was that many were older people who'd spent time outdoors in the evening. Meanwhile, a fifth patient showed up with symptoms typical of encephalitis, a viral inflammation of the brain. "If you see encephalitis in the late summer," commented Dr. John Roehrig of the CDC, "you have to think about viruses spread by mosquitoes."

August 31
The CDC sent epidemiologists to New York City to investigate an outbreak of what was then being called "encephalitis of unknown etiology [origin]." The field investigation found numerous mosquito-breeding sites and larvae in patients' yards and neighborhood.

September 3
The CDC completed tests on specimens from the sick people. They tested for antibodies against six common, insect-transmitted viruses. The tests came back positive for St. Louis encephalitis (SLE), and the CDC announced an outbreak. North America is home to several encephalitis viruses, of which SLE is the most common. It's transmitted to humans by mosquitoes which have bitten infected birds; the birds don't get sick. It hadn't been seen in the New York area since the 1970s, but outbreaks occur periodically in the Midwest and Southeast, primarily among the elderly. Scientists figured they'd solved the mystery, though an article in The New York Times described the outbreak as "freakish." The virus was thought to be the result of a bad drought followed by a downpour that created a perfect breeding environment for the mosquitoes that carry the virus. The mayor announced a $6 million campaign to wipe out the city's mosquitoes. Massive amounts of insect repellent were passed out free, along with brochures about the disease. Helicopters sprayed an insecticide called malathion across the city--alarming many people as much as the threat of St. Louis encephalitis.
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