The diversity of the more than 200 Bunyavirus species is reflected in their clinical importance. For example, human infections caused by Nairovirus, the causative agent of Crimean-Congo hemorrhagic fever, are associated with high morbidity and mortality. Therefore, handling of these viruses is done in biosafety level laboratories.
Hantaviruses represent a medically important member of the order Bunyavirales. They occur worldwide, being relatively common in Korea, Scandinavia (including Finland), Russia, western North America, and parts of South America. Hantavirus infections are associated with high fever, pulmonary edema, and respiratory failure. The mortality rate varies widely depending on the form, being as high as 50% for New World hantaviruses (the Americas), up to 15% for Old World hantaviruses (Asia and Europe), and about 0.1% for Puumala virus (primarily in Scandinavia). Antibody response plays an important role in reduction.
Bunyavirales form enveloped, spherical virions with diameters of 80-120 nm. The viruses do not contain matrix proteins. Bunyaviruses have two- or three-part genomes consisting of a large (L) and small (S) or large (L), medium (M), and small (S) RNA segments. The total genome size ranges from 10.5 to 22.7 kbp. The RNA segments are single-stranded and present in a helical formation within the virion. They also have a pseudo-circular structure due to the complementary ends of the individual segments. The L segment encodes RNA-dependent RNA polymerase, which is required for viral RNA replication and mRNA synthesis. The M segment encodes the viral glycoproteins that protrude from the viral surface and help the virus attach to and invade the host cell. The S segment encodes the nucleocapsid protein (N). Integrins have been described as possible attachment receptors for the humapathogenetically important hantavirus.