A Bridgeport grandmother is receiving a rabies vaccine after being bitten by a bat on her 84th birthday, city officials said Wednesday. Elvin "Gus" Agosto said his grandmother, who lives on the Upper East Side, caught the bat using a curtain after the flying mammal had entered her apartment through an open window - but she got bitten in the process. "We're using the incident as a teaching moment for the public," said Mayor Joe Ganim at the Beardsley Zoo Wednesday, in front of a live bat display. "Bats perform a crucial function in our ecosystem, especially during the summer, by eating thousands of mosquitos -- but people should avoid touching bats to minimize the chances of getting rabies," Ganim said. Experts say to call for help and let Animal Control do the rest.