A rodent of the genus Rattus, found in and around human habitations. In addition to causing economic loss from crop destruction, rats are of primary importance in the spread of human and animal diseases. They are hosts of various protozoans, flukes, tapeworms, and threadworms, and reservoirs of amebiasis, murine and scrub typhus, and bubonic plague. Typhus and plague are transmitted to people mainly by the rat flea. Rats also transmit rat-bite fever.