Bunyavirus - Morphology, Classification, Antigen

Classification of Bunyavirus

Classification of Bunyavirus is done by:

Realm: Riboviria

Kingdom: Orthornavirae

Phylum: Negarnaviricota

Subphylum: Polyploviricotina

Class: Ellioviricetes

Order: Bunyavirales

This order Bunyavirales contains 477 virus species which are grouped into 12 families.

• Cruliviridae - includes crustacean infecting bunyaviruses

• Fimoviridae - infect plants

• Leishbunyaviridae - infects protozoans

• Mypoviridae

• Phasmaviridae

• Tospoviridae - infects insects of Thysanoptera order

• Wupedeviridae

Medically important families in this order include:

• Arenaviridae - Lassa fever, Argentine hemorrhagic fever

• Hantaviridae - Hantavirus

• Nairoviridae - Crimean–Congo hemorrhagic fever

• Peribunyaviridae - California encephalitis virus, Jamestown Canyon virus, La Crosse encephalitis virus, Oropouche orthobunyavirus, Bwamba Fever

• Phenuiviridae - Rift Valley fever

Introduction of Bunyavirus

Bunyaviruses are vector-borne viruses. With the exception of Arenaviruses and Hantaviruses, all viruses in the Bunyaviridae family are transmitted by arthropods (mosquitoes, ticks, or sandflies). Meanwhile, Hantaviruses are transmitted through contact with clear mice feces.

Incidence of infection is closely linked to vector activity for example. Mosquito-borne viruses are more common in the summer.

Human infections with certain Bunyavirus, such as the Crimean-Congo Hemorrhagic fever virus are associated with high levels of morbidity and mortality, consequently handling of these viruses must occur with a Biosafety 4 laboratory.

They are also the cause of severe fever with thrombocytopenia syndrome. Hantavirus or Hantavirus hemorrhagic fever, common in Korea, Scandinavia, Russia, and Western North America is associated with high fever, lung edema, and pulmonary failure.

Morphology of Bunyavirus

Morphologically, bunyaviruses are spherical, enveloped particles 90-100 nm in diameter. They contain single-stranded RNA, which, with the nucleoprotein, forms three nucleocapsid segments. The segments are large, medium, and small helical, circular structures.

The RNA has a total molecular weight of 5x10⁶. The nucleocapsid is surrounded by a lipid-containing envelope. Surface spikes are composed of two glycoproteins that confer properties of neutralization of infectivity and hemagglutination of RBC

Bunyaviridae have a tripartite genome consisting of a large (L), medium (M), and small (s) RNA segment. These RNA segments are -ve ss and exist in a helical formation within the virion

• The L segment encodes the RNA-dependent RNA polymerase, necessary for viral RNA replication and mRNA synthesis

• The M segment encodes the viral glycoproteins, which project from the viral surface and aid the virus in attaching to and entering the host cell

• The S segment encodes the nucleocapsid protein (N)

The L and M segment is a negative sense. For the Genera of Phlebovirus, the S segment is ambisense. Ambisense means that some of the genes on the RNS strand are negative sense and others are positive sense.

The S segment codes for the viral nucleoprotein (N) in the negative sense and a nonstructural (Nss) protein in ambisense.

Classification and Antigen types of family Bunyaviridae

The family Bunyaviridae includes 4 genera containing 35 serogroups with at least 304 viruses of which 51 in the four genera are known to cause human disease

• Genus: Hantavirus; type species: Hantaan virus

• Genus: Nairovirus; type species: Crimean-Congo hemorrhagic fever virus

• Genus: Bunyavirus; type species: Bunyanwera virus

• Genus: Phlebavirus; type species: Rift Valley Fever virus