Rattus norvegicus is one of best known and most common rats, also called the brown rat. With rare exceptions, the brown rat lives wherever humans live, particularly in urban areas. Although brown rats may carry a number of pathogens which can result in disease, they are sometimes mistakenly thought to be a major reservoir of bubonic plague, a possible cause of The Black Death. However, the bacterium responsible is commonly endemic in only a few rodent species and is usually transmitted by rat fleas - common rodents include ground squirrels and wood rats. However, brown rats may suffer from plague, as can many non-rodent species including dogs, cats, and humans.