Biology and Diseases of Rats

The laboratory rat, Rattus norvegicus, is within the order Rodentia and family Muridae. The genus Rattus contains at least 56 species (retrieved January 28, 2014, from the Integrated Taxonomic Information System online database http://www.itis.gov); however, the Norway rat, R. norvegicus, and the black rat, R. rattus, are the two species most commonly associated with the genus. Rattus rattus preceded R. norvegicus in migration from Asia to Europe and the Americas by several hundred years. The former species reached Europe in the 12th century, and the Americas in the 16th century; whereas, R. norvegicus emerged in the 18th century in Europe and in the 19th century in the Western Hemisphere. Globally, the Norway rat has largely displaced the black rat, probably because of the Norway rat’s larger size and aggressiveness. The domestication and introduction of the albino R. norvegicus is rooted by its use in Europe and America in the 1800s as prey for a sport (rat baiting) in which individuals would wager on which terrier dog would most swiftly kill the largest number of rats confined to a pit. Because of the large numbers of rats needed for this sport, wild rats were purpose-bred, and albinos were selected out by some people as a hobby (Robinson, 1965; Mayhew, 1851).