INTRODUCTION
CLINICAL NOTE
The original habitat of the Norwegian or brown rat (Rattus Norvegicus) is Asia where they lived in burrows on the plains of north China and Mongolia. The black rat (Rattus rattus) comes from India and the Malaysian peninsula.
In the Middle Ages the black rat spread to the rest of the world when trade routes opened from the East. The brown rat followed later, arriving in Europe in the early 18th century, and rat baiting became a popular sport. Following the routes of human migration it reached America by the end of the century (Harkness & Wagner 1995).The brown rat became more successful due to its greater ability to withstand cold and live in close proximity to humans. Its omnivorous diet meant it could adapt to every environment from sewers to drains and buildings (Koolhaas 1999; Sharp & LaRegina 1998).
Rattus norvegicus was the first species to be domesticated purely for scientific purposes and is now the most widely studied experimental animal in biomedical research.
Longevity
The average life span of a rat is 2.5-3.5 years, with the females living longer, on average (Fallon 1996). Longevity can be increased by feeding a low fat and vegetable protein diet (Yu 1994).