Rift Valley fever

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Rift Valley fever
Arabia[1]

Rift Valley fever (RVF) is a

liver problems which may occur within the first few days. Those who have bleeding have a chance of death as high as 50%.[1]

The disease is caused by the RVF

antibodies against the virus or the virus itself in the blood.[1]

Prevention of the disease in humans is accomplished by vaccinating animals against the disease. This must be done before an outbreak occurs because if it is done during an outbreak it may worsen the situation. Stopping the movement of animals during an outbreak may also be useful, as may decreasing mosquito numbers and avoiding their bites. There is a human vaccine; however, as of 2010 it is not widely available. There is no specific treatment and medical efforts are supportive.[1]

Arabia. Outbreaks usually occur during periods of increased rain which increase the number of mosquitoes.[1] The disease was first reported among livestock in Rift Valley of Kenya in the early 1900s,[2] and the virus was first isolated in 1931.[1]

Signs and symptoms

In humans, the virus can cause several syndromes. Usually, they have either no symptoms or only a mild illness with fever,

hemorrhagic fever syndrome, meningoencephalitis (inflammation of the brain and tissues lining the brain), or affect the eye. Patients who become ill usually experience fever, generalised weakness, back pain, dizziness, and weight loss at the onset of the illness. Typically, people recover within two to seven days after onset. About 1% of people with the disease die of it. In livestock, the fatality level is significantly higher. Pregnant livestock infected with RVF abort virtually 100% of foetuses. An epizootic (animal disease epidemic) of RVF is usually first indicated by a wave of unexplained abortions.[citation needed
]

Other signs in livestock include vomiting and diarrhea, respiratory disease, fever, lethargy, anorexia and sudden death in young animals.[3]

Cause

Virology

Rift Valley fever phlebovirus
Prototypic phlebovirus virion and genome organization
Phlebovirus virion and genome
Virus classification Edit this classification
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum:
Negarnaviricota
Class: Ellioviricetes
Order: Bunyavirales
Family: Phenuiviridae
Genus: Phlebovirus
Species:
Rift Valley fever phlebovirus

The virus belongs to the

endosomal membrane.[citation needed
]

The virus' G(C) protein has a class II membrane fusion protein architecture similar to that found in flaviviruses and alphaviruses.[4] This structural similarity suggests that there may be a common origin for these viral families.[citation needed]

The virus' 11.5

kb tripartite genome is composed of single-stranded RNA. As a Phlebovirus, it has an ambisense genome. Its L and M segments are negative-sense, but its S segment is ambisense.[5] These three genome segments code for six major proteins: L protein (viral polymerase), the two glycoproteins G(N) and G(C), the nucleocapsid N protein, and the nonstructural NSs and NSm proteins.[6]

Transmission

The virus is transmitted through mosquito

aba roundleaf bat (Hipposideros abae), which are believed to be reservoirs for the virus.[12]

Pathogenesis

Although many components of the RVFV's RNA play an important role in the virus' pathology, the nonstructural protein encoded on the S segment (NSs) is the only component that has been found to directly affect the host. NSs is hostile and combative against the host interferon (IFNs) antiviral response.[13] IFNs are essential in order for the immune system to fight off viral infections in a host.[14] This inhibitory mechanism is believed to be due to a number of reasons, the first being, competitive inhibition of the formation of the transcription factor.[13] On this transcription factor, NSs interacts with and binds to a subunit that is needed for RNA polymerase I and II.[13][15] This interaction cause competitive inhibition with another transcription factor component and prevents the assembly process of the transcription factor complex, which results in the suppression of the host antiviral response.[13][15] Transcription suppression is believed to be another mechanism of this inhibitory process.[13] This occurs when an area of NSs interacts with and binds to the host's protein, SAP30 and forms a complex.[13][15] This complex causes histone acetylation to regress, which is needed for transcriptional activation of the IFN promoter.[15] This causes IFN expression to be obstructed. Lastly, NSs has also been known to affect regular activity of double-stranded RNA-dependent protein kinase R. This protein is involved in cellular antiviral responses in the host. When RVFV is able to enter the host's DNA, NSs forms a filamentous structure in the nucleus. This allows the virus to interact with specific areas of the host's DNA that relates to segregation defects and induction of chromosome continuity. This increases host infectivity and decreases the host's antiviral response.[13]

Diagnosis

Diagnosis relies on viral isolation from tissues, or serological testing with an

cell culture, and IgM antibody assays.[16] As of September 2016, the Kenya Medical Research Institute (KEMRI) has developed a product called Immunoline, designed to diagnose the disease in humans much faster than in previous methods.[17]

Prevention

A person's chances of becoming infected can be reduced by taking measures to decrease contact with blood, body fluids, or tissues of infected animals and protection against mosquitoes and other bloodsucking insects. Use of mosquito repellents and bed nets are two effective methods. For persons working with animals in RVF-endemic areas, wearing protective equipment to avoid any exposure to blood or tissues of animals that may potentially be infected is an important protective measure.[18] Potentially, establishing environmental monitoring and case surveillance systems may aid in the prediction and control of future RVF outbreaks.[18]

No vaccines are currently available for humans.[18][1] While a vaccines have been developed for humans, it has only been used experimentally for scientific personnel in high-risk environments.[1] Trials of a number of vaccines, such as NDBR-103 and TSI-GSD 200, are ongoing.[19] Different types of vaccines for veterinary use are available. The killed vaccines are not practical in routine animal field vaccination because of the need of multiple injections. Live vaccines require a single injection but are known to cause birth defects and abortions in sheep and induce only low-level protection in cattle. The live-attenuated vaccine, MP-12, has demonstrated promising results in laboratory trials in domesticated animals, but more research is needed before the vaccine can be used in the field. The live-attenuated clone 13 vaccine was recently registered and used in South Africa. Alternative vaccines using molecular recombinant constructs are in development and show promising results.[18]

A vaccine has been conditionally approved for use in animals in the US.[20] It has been shown that knockout of the NSs and NSm nonstructural proteins of this virus produces an effective vaccine in sheep as well.[21]

Epidemiology

Distribution of Rift Valley fever in Africa: Blue, countries with endemic disease and substantial outbreaks of RVF; green, countries known to have some cases, periodic isolation of virus, or serologic evidence of RVF

RVF outbreaks occur across sub-Saharan Africa, with outbreaks occurring elsewhere infrequently. Outbreaks of this disease usually correspond with the warm phases of the EI Niño/Southern Oscillation. During this time there is an increase in rainfall, flooding and greenness of vegetation index, which leads to an increase in mosquito vectors.[22] RVFV can be transmitted vertically in mosquitos, meaning that the virus can be passed from the mother to her offspring. During dry conditions, the virus can remain viable for a number of years in the egg. Mosquitos lay their eggs in water, where they eventually hatch. As water is essential for mosquito eggs to hatch, rainfall and flooding cause an increase in the mosquito population and an increased potential for the virus.[23]

The first documented outbreak was identified in Kenya in 1931, in sheep, cattle and humans;

East Africa (2006–2007),[30] Sudan (2007),[31] South Africa (2010),[32][33] Uganda (2016),[34] Kenya (2018),[35] and Mayotte (2018–2019).[36] 2020–2021 in Kenya,[37]
in 2022 an outbreak is ongoing in Burundi.

Biological weapon

Rift Valley fever was one of more than a dozen agents that the

biological weapons before the nation suspended its biological weapons program in 1969.[38][39]

Research

The disease is one of several identified by

Ebola epidemic for urgent research and development toward new diagnostic tests, vaccines and medicines.[40][41]

See also

References

  1. ^ a b c d e f g h i j k l m n o p "Rift Valley fever". Fact sheet N°207. World Health Organization. May 2010. Archived from the original on 15 April 2014. Retrieved 21 March 2014.
  2. from the original on 2017-09-08.
  3. ^ a b Rift Valley Fever Archived 2012-05-08 at the Wayback Machine reviewed and published by WikiVet, accessed 12 October 2011.
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  5. ^ "ViralZone: Phlebovirus". viralzone.expasy.org. Archived from the original on 2016-10-03. Retrieved 2016-09-14.
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  17. ^ "Kemri develops kit for rapid test of viral disease". Archived from the original on 2016-09-06. Retrieved 2016-09-14.
  18. ^ a b c d "Prevention: Rift Valley Fever | CDC". US Centers for Disease Control and Prevention. Retrieved 24 September 2018. Public Domain This article incorporates text from this source, which is in the public domain.
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  23. ^ "Rift Valley Fever | CDC". www.cdc.gov. Archived from the original on 2016-12-04. Retrieved 2016-12-01.
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  30. ^ "At least 75 people die of Rift Valley Fever in Kenya". International Herald Tribune. 7 January 2007. Archived from the original on 9 January 2007.
  31. ^ "Deadly fever spreads Kenya Panic". BBC. 26 January 2007. Archived from the original on 1 May 2008.
  32. ^ ProMED-mail Archived 2011-07-28 at the Wayback Machine. ProMED-mail. Retrieved on 2014-05-12.
  33. ^ "Rift Valley fever in South Africa". WHO. Archived from the original on 2010-04-12.
  34. ^ "Outbreak Summaries | Rift Valley Fever | CDC". 2019-02-15.
  35. ^ "Rift Valley fever – Kenya". WHO. 18 June 2018. Archived from the original on June 23, 2018. Retrieved 1 July 2018.
  36. ^ "Rift Valley Fever – Mayotte (France)". WHO. 13 May 2019. Archived from the original on July 1, 2019. Retrieved 15 May 2019.
  37. ^ "Rift Valley fever – Kenya". World Health Organization. 12 February 2021. Archived from the original on February 12, 2021. Retrieved 24 February 2021.
  38. ^ "Chemical and Biological Weapons: Possession and Programs Past and Present", James Martin Center for Nonproliferation Studies, Middlebury College, April 9, 2002, accessed November 14, 2008.
  39. ^ "Select Agents and Toxins" (PDF). USDA-APHIS and CDC: National Select Agent Registry. 2011-09-19. Archived from the original (PDF) on 2012-02-25.
  40. ^ Kieny MP. "After Ebola, a Blueprint Emerges to Jump-Start R&D". Scientific American Blog Network. Archived from the original on 20 December 2016. Retrieved 13 December 2016.
  41. ^ "List of Pathogens". World Health Organization. Archived from the original on 20 December 2016. Retrieved 13 December 2016.

External links