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|Isolated male diagnosed with Crimean-Congo hemorrhagic fever|
|Group:||Group V ((−)ssRNA)|
Bunyavirales is an order of negative-sense single-stranded RNA viruses. It was formerly known as Bunyaviridae family of virus.
In 2017, the ICTV reclassified the family Bunyaviridae as Bunyvirales, a taxonomic shift from a family of viruses to an order of viruses. The body made these decisions in a 2016 convening in Budapest. Primary reasons for this alteration revolve around these observations: approximately half of viruses in the former Bunyaviridae were at the time unassigned to a genus; novel viruses discovered that were characteristic of and clustered around Bunyaviridae based on phylogenetic analyses had bi-segmented genomes (as opposed to Bunyaviridae's tri-segmentation); and plant viruses also lacking tri-segmentation were previously known to be "bunya-like" yet were not properly assigned to the family Bunyaviridae based upon the past taxonomic classifications. All five genera formerly in the family Bunyaviridae (Hantavirus, Nairovirus, Orthobunyavirus, Phlebovirus, Tospovirus) are now novel viral families, some of which have been combined. These new families include: Hantaviridae, Feraviridae, Fimoviridae, Jonviridae, Nairoviridae, Peribunyaviridae, Phasmaviridae, Phenuiviridae, and Tospoviridae.
This order of viruses belong to the fifth group of the Baltimore classification, the so called negative-sense single stranded ribonucleic acid (−)ssRNA. They are enveloped RNA viruses. Though generally found in arthropods or rodents, certain viruses in this order occasionally infect humans. Some of them also infect plants.
Bunyaviridae are vector-borne viruses. With the exception of Hantaviruses, all viruses in the Bunyavirales order are transmitted by arthropods (mosquitos, tick, or sandfly). Hantaviruses are transmitted through contact with deer 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 Bunyavirales, such as Crimean-Congo hemorrhagic fever virus, are associated with high levels of morbidity and mortality, consequently handling of these viruses must occur with a Biosafety level 4 laboratory. They are also the cause of severe fever with thrombocytopenia syndrome.
Hanta virus or Hantavirus Hemorrhagic fever, common in Korea, Scandinavia, Russia, and western North America, is associated with high fever, lung edema and pulmonary failure. Mortality is around 55%. The antibody reaction plays an important role in decreasing levels of viremia.
Yosemite Outbreak: The Yosemite outbreak lead to the restructuring of preventative measures for park employees. New policies emphasize extensive use of cleaning practices, use of personal protective equipment (PPE), and education of Hantavirus safety training and knowledge of HPS to Yosemite employees. During the time of the outbreak in 2012, the park was required to provide information regarding Hantavirus risks, signs, and symptoms to all tourists who were staying at the camp before September 17th, 2012. Information flyers regarding Hantavirus were posted through the park, and emergency call centers specifically for Hantavirus were required to be accessible and staffed from 9 am to 5 pm.
There are currently about 330 viruses recognised in this order.
The order Bunyavirales contains the families for example:
- Family Hantaviridae; type species: Hantaan virus
- Family Nairoviridae; type species: Dugbe virus
- Family Peribunyaviridae (which contains former genus Orthobunyavirus); type species: Bunyamwera virus
- Family Phenuiviridae (which contains former genus Phlebovirus; type species: Rift Valley fever virus
- Family Tospoviridae; type species: Tomato spotted wilt virus
- Family Feraviridae; type species: Ferak Virus
- Family Fimoviridae; type species: Fig mosaic emaravirus
- Family Jonviridae; type species: Jonchet orthojonvirus
- Family Phasmaviridae; type species: Phasmavirus, Wuhan mosquito virus
Plants can host Bunyaviruses from the Tospoviridae and Fimoviridae families (tomato, pigeonpea, melon, wheat, raspberry, redbud, rose).
Bunyaviridae have tripartite genomes consisting of a large (L), medium (M), and small (S) RNA segment. These RNA segments are single-stranded, and exist in a helical formation within the virion. Besides, they exhibit a pseudo-circular structure due to each segment's complementary ends. 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 are negative sense. For the Genera of Phlebovirus and Tospovirus, the S segment is ambisense. Ambisense means that some of the genes on the RNA 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.
This ambisense arrangement requires two rounds of transcription to be carried out. First the negative sense RNA is transcribed to produce mRNA and a full length replicative intermediate. From this intermediate a subgenomic mRNA encoding the small segment nonstructural protein is produced while the polymerase produced following the first round of transcription can now replicate the full length RNA to produce viral genomes.
Bunyavirus RNA replicates in the cytoplasm, while the viral proteins transit through the ER and Golgi apparatus. Mature virions bud from the Golgi apparatus into vesicles which are transported to the cell surface.
Diseases in humans
Bunyaviruses that cause disease in humans include:
- California encephalitis virus vector: mosquitoes
- Hantavirus reservoir small mammals or rodents, vector:
- Crimean–Congo hemorrhagic fever reservoir and vector: ticks, amplifying hosts and vector: small mammals, domestic mammals,
- Rift Valley fever reservoir: bats, vector: mosquitoes, amplifying hosts: small mammals, domestic mammals,
- Bwamba Fever env. reservoir: monkeys vector: mosquitoes, amplifying hosts: donkeys
- Severe fever with thrombocytopenia syndrome
Bunyaviruses have segmented genomes, making them capable of rapid recombination and increasing the risk of outbreak. Bunyaviridae are transmitted by hematophagous arthropods including mosquitoes, midges, flies, and ticks. The viral incubation period is about 48 hours. Symptomatic infection typically causes non-specific flu-like symptoms with fever lasting for about three days. Because of their non-specific symptoms, Bunyavirus infections are frequently mistaken for other illnesses. For example, Bwamba fever is often mistaken for malaria.
Prevention depends on the reservoir, amplifying hosts and how the viruses are transmitted, ie the vector, whether ticks or mosquitoes and which animals are involved.
Preventative measures include general hygiene, limiting contact with vector saliva, urine, feces, or bedding.
There are no licensed vaccine for bunyaviruses.
As precautions Cache Valley virus and Hantavirus research should be conducted in BSL-2 (or higher), Rift Valley Fever virus research be conducted in BSL-3 (or higher), Congo-Crimean Hemorrhagic Fever virus research be conducted in BSL-4 laboratories, per CDC.
1940´s: Crimean–Congo hemorrhagic fever is discovered in Russia
1951: 3,000 cases of Hantavirus were reported in South Korea in 1951, a time when UN forces were fighting on the 38th parallel during the Korean War
1977: Rift Valley Fever virus caused approximately 200,000 cases and 598 deaths in Egypt
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