It was around 4 a.m. when the tumult began. “I’m falling out of bed!” my grandmother screamed. Half asleep, my grandfather tried to push her back in, but when he touched her, she shrieked and began sobbing. He rushed down the hallway, phoned the hospital, and was told to call 911. By the time that he could get back to the bedroom, my grandmother was slumped on the floor, her head against the bedside table, babbling incoherently. The paramedics arrived within 15 minutes.

“I wasn’t thinking of it being anything,” my grandfather says now. “I thought it was something she would get treated for and get better.”

My grandmother—or Oma, as we call her, the German word for grandmother—had always been a picture of perfect health, a trait that she and Opa, my grandfather, attributed to decades spent farming organic produce and tending to their land. But as Oma spent the next 32 days in the hospital and then three weeks in a rehabilitation facility, my family came to realize that the first night of terror was just the beginning. Despite the best efforts of her doctors, Oma did not get better.

* * *

On August 23, 1999, an infectious disease doctor in northern Queens reported two patients with encephalitis—swelling of the brain—to the New York City Department of Health, according to a Centers for Disease Control and prevention (CDC) report from October 1999. Upon investigation, the health department identified six patients with identical diagnoses who lived in the same vicinity.

In what appeared to be an unrelated development, crows were being found dead all over New York state that summer. It was as if they were dropping from the sky. In early September, a cormorant, two captive-bred Chilean flamingoes, and an Asian pheasant died at the Bronx Zoo. The unexplained deaths filled the papers with foreboding stories. It was thought that mosquitoes were spreading some kind of virus, but which one, and whether it could spread to humans, was unknown.

The local mosquito vector control agency jumped into action and began spraying pesticides. About 300,000 cans of DEET-based mosquito repellent and 750,000 pamphlets with information about personal protection against mosquito bites were distributed to NYC residents, according to the same CDC report.

On September 20, samples from the deceased birds at the Bronx Zoo were tested and sent to the CDC. DNA sequencing revealed a viral strain, closely related to West Nile virus found in other parts of the world, but never before found in the Western Hemisphere. Around the same time, the CDC, while performing tests on a human brain specimen from an encephalitis case, discovered a strain of West Nile virus identical to the one found in the bird. Over the course of the next few months, the same match between the viruses in the birds and those in humans was found dozens of times. A previously undetected strain of West Nile virus, it seemed, was now in the United States.