Hemorrhagic fevers of the family Bunyaviridae

The Bunyaviridae family includes more than 250 serotypes of viruses, which are part of five genera: Bunyavirus, Phlebovirus, Nairovirus, Hantavirus, Tospovirus. The typical viruses of these genera are: Bunyamwera virus, Sicily mosquito fever virus, Nairobi sheep disease virus and Hantaan virus, respectively. Tospoviruses are nonpathogenic to humans and affect plants.

The prototype of the viruses of this family is the Bunyamwera virus, first isolated in Central Africa and transmitted by mosquitoes (the virus is named after the Bunyamwera region in Uganda).

Characteristics of hemorrhagic fevers of the Bunyaviridae family

Name	Genus of virus	Carrier	Spreading
Rift Valley GL (Rift Valley GL)	Phlebovirus	Aedes mcintoshi, Aedes vexans and others	Tropical Africa
Crimea-Congo GL	Nairovirus	Ixodid ticks of the genus Hyalomma	Africa, southern Russia, the Middle East, Central Asia, the Balkans, China
Hemorrhagic fever with renal syndrome	Phlebovirus	Aedes mcintoshi, Aedes vexans and others	Tropical Africa
Crimea-Congo GL	Hantavirus	Mouse-like rodents	Europe, Asia.
Hemorrhagic fever with renal syndrome	Hantavirus	Mouse-like rodents	Europe, Asia.
Hantavirus pulmonary syndrome	Hantavirus	Rats and mice of various genera	South and North America

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ], [ 8 ], [ 9 ], [ 10 ]

Resistance of viruses to physical and chemical factors

Bunyaviruses are sensitive to ether and detergents, are inactivated by heating to 56 °C for 30 minutes and almost instantly by boiling, but retain infectious activity for a long time when frozen. Bunyaviruses are stable in a very limited range of pH values - 6.0-9.0, and are inactivated by commonly used disinfectants.

Morphology

Virions are oval or spherical in shape, 80-120 nm in diameter, and resemble a donut under electron microscopy. These are complex RNA genomic viruses containing three internal nucleocapsids with a helical symmetry type. Each nucleocapsid consists of a nucleocapsid protein N, a unique single-stranded minus RNA, and a transcriptase enzyme (RNA-dependent RNA polymerase). The three RNA segments associated with the nucleocapsid are designated by size: L (long), M (medium), and S (short). RNA does not have infectious activity. Unlike other viruses with a minus RNA genome (Orthomixoviridae, Paramixoviridae, and Rhabdoviridae), bunyaviruses do not contain an M protein, so they are more flexible. The core of the virion, containing ribonucleoprotein (RNP), is surrounded by a lipoprotein membrane, on the surface of which are spikes - glycoproteins G1 and G2, which are encoded by the M-segment of RNA.

Antigens

Protein N is a carrier of group-specific properties and is detected in the CSC. Glycoproteins (G1 and G2) are type-specific antigens detected in the RN and RTGA. These are protective antigens that determine hemagglutinating properties, which are not as pronounced in bunyaviruses as in orthomyxo- and paramyxoviruses. They induce the formation of virus-neutralizing antibodies. Glycoproteins are the main determinants of pathogenicity, determining the cellular organotropy of viruses and the efficiency of their transmission by arthropods.

Based on the cross-linking analysis in the RSC, bunyaviruses are grouped into genera, within which they are distributed into serogroups based on the cross-linking RN and RTGA.

[ 11 ], [ 12 ], [ 13 ], [ 14 ], [ 15 ], [ 16 ], [ 17 ], [ 18 ], [ 19 ]

Reproduction of bunyaviruses

Bunyaviruses reproduce in the cytoplasm of the cell, where RNPs are first formed. Three types of mRNA are formed, each of which codes for a corresponding polypeptide - L, N, and precursors of proteins G1 and G2. Viral proteins are synthesized quickly in an infected cell. Thus, protein N can be detected after 2 hours, and G1 and G2 - after 4 and 6-8 hours, respectively. Viral maturation (acquisition of an external lipid-containing membrane) as a result of RNP budding, unlike other viruses, does not occur on the plasma membranes of the cell, but when passing through the walls of vesicles in the Golgi apparatus. Subsequently, viral particles are transported to the plasma membrane (cell membrane). The release of viral particles occurs by exocytosis, and sometimes by cell lysis. Bunyaviruses, like other representatives of arboviruses, have the ability to reproduce in two temperature conditions: 36-40 and 22-25 °C, which allows them to reproduce not only in the body of vertebrates, but also in the body of carriers - blood-sucking arthropod insects.

Features of bunyavirus cultivation and susceptibility of laboratory animals to them

Newborn white mice, white rats and hamsters are susceptible to bunyaviruses when they infect the brain. To cultivate viruses, cell cultures from carriers, human embryonic kidneys, BHK-21, chicken embryo fibroblasts are used, where they do not exert a pronounced CPE. Viruses can be cultivated in chicken embryos. A universal model for isolating arboviruses is the infection of newborn white mice, in which they cause the development of encephalitis, which ends fatally.

[ 20 ], [ 21 ], [ 22 ], [ 23 ], [ 24 ], [ 25 ], [ 26 ]