The issue should be reported to the landlord so he can take care of it and have the place exterminated. If you are not actually a tenant in the house, there is not much more you can do. If you feel as though this poses a health issue in the surrounding area, you can get in touch with NYC information by dialing 311 from any phone, or you can go to the NYC.gov web site page pertaining to rat infestations here:
If I can be of further assistance please contact me direct. Good luck!
Mitchell S. Feldman
Associate Broker/ Director of Sales/ e-Pro Realtor
Fillmore Real Estate
Office: (718) 252-2000/ Cell: (917) 805-0783