Hantaviruses (family Bunyaviridae) are enveloped viruses that contain a tripartite, negative-stranded RNA genome encoding an RNA-dependent RNA polymerase (L), two integral membrane glycoproteins (G1 and G2), and a nucleocapsid (N) protein. The N protein is the most abundant viral component and the major antigen in early serological response in humans and mice. It has essential functions in viral RNA replication, encapsidation, and also in virus assembly. PUUV is a causative agent of a mild form of hemorrhagic fever with renal syndrome (nephropathia epidemica) mainly in Europe and it is transmitted by the red bank vole Clethrionomys glareolus. Puumala virus is a species of hantavirus. Humans infected with the virus may develop a haemorrhagic fever with renal syndrome (HFRS) known as nephropathia epidemica. Puumala virus HFRS is lethal in a small percentage of cases. Puumala virus is named after a municipality in Finland. The virus is found predominantly in Scandinavia and Finland, although it has also been reported elsewhere in Northern Europe and Russia. Because the bank vole (Myodes glareolus) acts as a reservoir for the virus, nephropathia epidemica cases track with the vole population in a three- to four-year cycle. Humans are infected through inhalation of dust from vole droppings.