 Domesticated rats have a longer lifespan than that of wild rats . Because domesticated rats are protected from predators and have ready access to food , water , shelter , and medical care , their average lifespan is around two to three years , in contrast to wild R. norvegicus which average a lifespan of less than one year . However , wild rats generally have larger brains , hearts , livers , kidneys , and adrenal glands than laboratory rats . The fancy rat and wild rat also both face a multitude of differing health concerns ; the former is at risk of developing a pneumococcal infection from exposure to humans , while the latter may harbor tapeworms after coming in contact with carriers like cockroaches and fleas . 
