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|Isolated male patient diagnosed with Crimean-Congo hemorrhagic fever (C-CHF)|
|Group:||Group V ((−)ssRNA)|
Bunyaviridae is a family of virus belonging 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 family occasionally infect humans. Some of them also infect plants.
Bunyaviridae are vector-borne viruses. With the exception of Hantaviruses, all viruses in the Bunyaviridae family 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 Bunyaviridae, 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 family.
The family Bunyaviridae contains the genera:
- Genus Hantavirus; type species: Hantaan virus
- Genus Nairovirus; type species: Dugbe virus
- Genus Orthobunyavirus; type species: Bunyamwera virus
- Genus Phlebovirus; type species: Rift Valley fever virus
- Genus Tospovirus; type species: Tomato spotted wilt virus
Two additional viruses may lie outside the previously defined taxa: Ferak virus (FERV) and Jonchet virus (JONV).
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
- Crimean-Congo hemorrhagic fever
- Rift Valley fever
- Bwamba Fever
- 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.
Because Hantavirus involves rodent-borne transmission, preventative measures include limiting contact with rodents or rodent saliva, urine, feces, or bedding. People can reduce the number of rodents that are found in residences by sealing up holes or cracks that may serve as entrances for rodents and by leaving out rodent traps. Campers are encouraged to not leave food out in the tents or campgrounds to prevent attracting rodents.
There is currently no licensed vaccine for Hantavirus in the United States. A Hantavirus vaccine (Hantavax) clinical trial was conducted in Yang-p'yung County, Kyonggi Province in South Korea. In a clinical trial study by Cho et al., 64 volunteers were given the first dose of 0.5 ml of a formalin-inactivated Hantavirus Vaccine (Hantavax) via intramuscular injection and a second dose thirty days after administration of the first dose. 97% of the volunteers who were vaccinated demonstrated seroconversion.
Research precautions: The CDC requires that Hantavirus research be conducted in BSL-2 (or higher) laboratories due to the virus’s ability to cause hemorrhagic fever. The CDC requires that Rift Valley Fever virus research be conducted in BSL-3 (or higher) laboratories. The CDC requires that Congo-Crimean Hemorrhagic Fever virus research be conducted in BSL-4 laboratories. The CDC requires that Congo-Crimean Hemorrhagic Fever virus research be conducted in BSL-2 (or higher) laboratories.[contradictory] The CDC requires that Cache Valley virus research be conducted in BSL-2 (or higher) laboratories.
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
1960: La Crosse virus was first recognized in a fatal case of encephalitis in La Crosse, Wisconsin
1977: Rift Valley Fever virus caused approximately 200,000 cases and 598 deaths in Egypt
1993: The first recorded United States outbreak of Hantavirus in the Four Corners (Arizona, Colorado, New Mexico, and Utah)
February 1999: Cho and Howard conduct clinical trials in Yang-p'yung County, Kyonggi Province in South Korea for a formalin-inactivated Hantavirus vaccine (Hantavax)
2012: Tourists visiting Yosemite National Park were infected with Hantavirus
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