Puumala virus

Puumala virus
Virus classification
(unranked):	Virus
Realm:	Riboviria
Kingdom:	Orthornavirae
Phylum:	Negarnaviricota
Class:	Ellioviricetes
Order:	Bunyavirales
Family:	Hantaviridae
Genus:	Orthohantavirus
Species:	Orthohantavirus puumalaense
Virus:	Puumala virus
Synonyms[1]
Puumala hantavirus Puumala orthohantavirus

Puumala virus (PUUV) is the main cause of hemorrhagic fever with renal syndrome (HFRS) in Europe and Russia. Puumala virus is transmitted by the bank vole (Clethrionomys glareolus). In its natural reservoir, PUUV causes a persistent infection with few symptoms and is spread through excretions, fighting, and grooming. Humans can become infected by inhaling aerosols that contain rodent saliva, urine, or feces, as well as through bites and scratches. In humans, infection is usually asymptomatic but can lead to a mild form of HFRS often called nephropathia epidemica (NE). Symptoms include fever and headache, impaired vision, as well as the appearance of spots on the skin and renal symptoms such as kidney swelling, excess protein in urine, blood in urine, decreased urine production, and kidney failure. The case fatality rate from infection is less than 1%.

The genome of PUUV is about 12 kilobases (kb) in length and segmented into three negative-sense, single-stranded RNA (-ssRNA) strands. The small strand encodes the viral nucleoprotein, the medium strand encodes the viral spike protein, which attaches to cell receptors for entry into cells, and a non-structural protein that interferes with interferon production, and the long strand encodes the viral RNA-dependent RNA polymerase (RdRp), which replicates and transcribes the genome. Genome segments are encased in nucleoproteins to form ribonucleoprotein (RNP) complexes that are surrounded by a viral envelope that contains spikes emanating from its surface.

Puumala virus replicates first by binding to the surface of cells with its envelope spikes. Virus particles, called virions, are then taken into the cell by endosomes, where a drop in pH causes the viral envelope to fuse with the endosome, which releases viral RNA into the host cell. RdRp then transcribes the genome for translation by host cell ribosomes and produces copies of the genome for progeny viruses. New virions are assembled at the endoplasmic reticulum and bud from its surface to obtain their viral envelope. Progeny viruses are then transported by a cellular vesicle to the cell membrane, where they leave the cell by exocytosis.

PUUV was discovered in 1980 after being extracted from bank voles. The virus was subsequently linked to a past outbreak among soldiers in Finland during World War Two, when the disease received the name nephropathia epidemica. A similar outbreak occurred among soldiers in Croatia during the Balkan Wars. PUUV is found throughout Europe and Russia where the vole bank lives. Finland is the country most affected by PUUV and experiences thousands of infections each year. While infection is typically associated with HFRS, Puumala virus can cause hantavirus pulmonary syndrome on rare occasions.