Bunyaviruses
Last reviewed: 23.04.2024
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The family Bunyaviridae (from the name of the Bunyamvera area in Africa) is the largest by the number of its included viruses (over 250). This is a typical ecological group of arboviruses. It is divided into five genera:
- Bunyavirus (over 140 viruses combined into 16 antigenic groups, and several ungrouped) - are transmitted mainly by mosquitoes, less often by slugs and ticks;
- Phlebovirus (about 60 representatives) - are transmitted mainly by mosquitoes;
- Nairobivirus (about 35 viruses) - transmitted by ixodid mites;
- Uukuvirus (22 antigenically related viruses) - also transmitted by ixodid mites;
- Hantavirus (more than 25 serovariants). In addition, there are several dozen Bunyaviruses not assigned to any of the genera.
Viruses contain single-stranded negative fragmented (3 fragments) RNA with a molecular weight of 6.8 MD. Nucleocapsid helical symmetry. Mature virions have a spherical shape and a diameter of 90-100 nm. The shell consists of a membrane 5 nm thick, covered with surface protrusions 8-10 nm in length. Surface protrusions consist of two glycopeptides that combine to form cylindrical morphological units 10-12 nm in diameter with a central cavity 5 nm in diameter. They are arranged in such a way that they form a surface grating. The membrane on which the surface subunits are fixed consists of bilayer lipids. A heavy nucleoprotein is located directly below the membrane. Bunyaviruses have three basic proteins: one protein bound to nucleocapsid (N), and two glycoproteins (G1 and G2) bound to the envelope. They reproduce in the cytoplasm of the cell, similarly to flaviviruses; maturation occurs by budding into intracellular vesicles, then the viruses are transported to the cellular surface. Have hemagglutination properties.
Bunyaviruses are sensitive to the effects of elevated temperature, fat solvents and temperature fluctuations. Very well preserved at low temperatures.
Bunyaviruses are cultured in chick embryos and in cell cultures. They form plaques in cell monolayers under agar. Can be isolated by infecting 1-2-day-old white suckling mice.
Among the diseases caused by bunyaviruses, mosquito fever (pappataci fever), California encephalitis, Crimean (Congo) hemorrhagic fever (KGL-Congo) are more common.
[Pathogenesis and symptoms of bunyavirus infections
The pathogenesis of many human bunyavirus infections has been studied relatively little, and the clinical picture has no characteristic symptoms. Even with diseases that occur with symptoms of CNS damage and hemorrhagic syndrome, the clinic varies from extremely rare severe cases with a lethal outcome to the latent forms that predominate.
The mosquito Phlebotomuspapatasi is the bearer of mosquito fever. The incubation period is 3-6 days, the onset of the disease is acute (fever, headache, nausea, conjunctivitis, photophobia, abdominal pain, and leukopenia). 24 hours before and 24 hours after the onset of the disease, the virus circulates in the blood. All the patients recover. Specific treatment is not. Prevention nonspecific (mosquito nets, the use of repellents and insecticides).
California encephalitis (a carrier of the genus Aedes) begins suddenly with a severe headache in the frontal region, an increase in temperature to 38-40 ° C, sometimes with vomiting, inhibited state and seizures.
Crimean (Congo) hemorrhagic fever occurs in the south of our country and in many other countries. Infection occurs when bites of mites of the genera Hyalomma, Rhipicephalus, Dermacentor, as well as by contact. The virus was isolated by MP Chumakov in 1944 in the Crimea. The incubation period is 3-5 days. The onset is acute (chills, fever). At the heart of the disease is an increase in the permeability of the vascular wall. The growing virusemia causes the development of hemorrhages, severe toxemia, up to infectious-toxic shock with disseminated intravascular coagulation. Mortality - 8-12%.
Immunity
As a result of the transferred bunyavirus infection, long-term immunity is formed due to the accumulation of virus neutralizing antibodies.
Laboratory diagnostics of bunyavirus infections
Bunyaviruses can be isolated from pathological material (blood, sectional material) with intracerebral infection of suckling mice, in which paralysis and death occur. Viruses are typified in the neutralization reaction, RSK, RPGA and RTGA. In the serological method, paired sera in the RN, RAC or RTGA are examined (note that hemagglutinin is absent in the Crimean hemorrhagic fever virus).