Emulated in MAME ! [Console] NES Game
Alien Syndrome © 1989 Tengen.
North American release. Game developed in Japan. For more information about the game itself, please see the original Japanese release entry; "Alien Syndrome [Model SAN-AZ]
Game description from the Tengen manual:
The year is 2089 of the Galactic Calendar. In this far-flung future, humans have colonized the outer planets. Without warning, the glory of this achievement turned into disaster: A horrible race of aliens has imprisoned an entire colony aboard its space ships! Each of these vessels houses countless numbers of slimy monsters led by a vicious alien boss. Having miraculously escaped capture, you must go from ship to ship in a valiant effort to save your fellow humans.