Nile Grass Rat, Arvicanthis niloticus, are medium-sized rats with stoutish bodies, widely distributed in sub Saharan Africa, but traditionally held to extend to the mouth of the Nile River. The genus rattus to which it belongs was introduced to Africa by Arab and European ships in sometimes well-documented progression. It is an important reservoir for Yersinia pestis, a bacterium that can infect humans with pneumonia. This rat species is also a valuable, spontaneous model for exploring the etiology and pathophysiology of Metabolic Syndrome as well as its various complications.