Lassa virus is a RNA virus belonging to the family of Arenaviridae. It was discovered as the causative agent of a hemorrhagic fever called Lassa fever which is an acute viral illness that occurs in west Africa and is estimated to affect some 100,000 people annually. The reservoir, or host, of Lassa virus is a rodent known as the “multimammate rat” (Mastomys natalensis). Once infected, this rodent is able to excrete virus in urine for an extended time period. Mild symptoms include slight fever, general malaise and weakness, and headache. In 20% of infected individuals, however, disease may progress to more serious symptoms including hemorrhaging, respiratory distress, repeated vomiting, facial swelling, pain in the chest, back, and abdomen, and shock.