City officials insist the insecticides are safe, but many New Yorkers say they're more afraid of the chemicals than of the threat of encephalitis. This Central Park biker is one. Central Park is one of the few places we come to exercise on weekends, and spraying the park doesn't leave New Yorkers with much other alternative to exercise and stuff. So we're very strongly against it. It is caused by a virus thought to occur naturally in birds.
Mosquitoes come into contact with the virus when they feed on the birds' blood.
When they move on to human targets, the mosquitoes then transmit the virus to people. The virus enters the body's cells and spreads to the brain, where it causes swelling and interrupted blood flow. Most infected people never show any of the flu-like symptoms and recover on their own, but cases of severe infection can result in death. The signs and symptoms in the next five to 15 days is what you want to watch for, okay. Since 1964, just under 4,500 cases of St. Louis Encephalitis have been reported to the Federal Centers for Disease Control, that's an average of 128 cases annually.