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Rift Valley fever

rift valley fever, rift valley fever vaccine
Rift Valley fever RVF is a viral disease that can cause mild to severe symptoms The mild symptoms may include: fever, muscle pains, and headaches which often last for up to a week The severe symptoms may include: loss of sight beginning three weeks after the infection, infections of the brain causing severe headaches and confusion, and bleeding together with 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 virus, which is of the Phlebovirus type It is spread by either touching infected animal blood, breathing in the air around an infected animal being butchered, drinking raw milk from an infected animal, or the bite of infected mosquitoes Animals such as cows, sheep, goats, and camels may be affected In these animals it is spread mostly by mosquitoes It does not appear that one person can infect another person The disease is diagnosed by finding antibodies against the virus or the virus itself in the blood1

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 supportive1

Outbreaks of the disease have only occurred in Africa and Arabia Outbreaks usually occur during periods of increased rain which increase the number of mosquitoes1 The disease was first reported among livestock in Rift Valley of Kenya in the early 1900s,2 and the virus was first isolated in 19311


  • 1 Signs and symptoms
  • 2 Cause
    • 21 Virology
    • 22 Transmission
  • 3 Pathogenesis
  • 4 Diagnosis
  • 5 Prevention
  • 6 Epidemiology
    • 61 Outbreaks
    • 62 2006/07 outbreak in Kenya and Somalia
    • 63 2010 South Africa outbreak
  • 7 Biological weapon
  • 8 Research
  • 9 References
  • 10 External links

Signs and symptomsedit

In humans, the virus can cause several syndromes Usually, sufferers have either no symptoms or only a mild illness with fever, headache, muscle pains, and liver abnormalities In a small percentage of cases < 2%, the illness can progress to 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

Other signs in livestock include vomiting and diarrhoea, respiratory disease, fever, lethargy, anorexia and sudden death in young animals3



Rift Valley fever virus
Virus classification
Group: Group V −ssRNA
Order: Unassigned
Family: Bunyaviridae
Genus: Phlebovirus
Species: Rift Valley fever virus

The virus belongs to the Bunyaviridae family This is a family of enveloped negative single stranded RNA viruses All Bunyaviruses have an outer lipid envelope with two glycoproteins—GN and GC—required for cell entry They deliver their genome into the host-cell cytoplasm by fusing their envelope with an endosomal membrane

The virus' GC protein has a class II membrane fusion protein architecture similar to that found in flaviviruses and alphaviruses4 This structural similarity suggests that there may be a common origin for these viral families

The virus' 115 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 ambisense5 These three genome segments code for six major proteins: L protein viral polymerase, the two glycoproteins GN and GC, the nucleocapsid N protein, and the nonstructural NSs and NSm proteins


See also: Prevention of viral hemorrhagic fever

The virus is transmitted through mosquito vectors, as well as through contact with the tissue of infected animals Two species—Culex tritaeniorhynchus and Aedes vexans—are known to transmit the virus6 Other potential vectors include Aedes caspius, Aedes mcintosh, Aedes ochraceus, Culex pipiens, Culex antennatus, Culex perexiguus, Culex zombaensis and Culex quinquefasciatus789 Contact with infected tissue is considered to be the main source of human infections10 The virus has been isolated from two bat species: the Peter's epauletted fruit bat Micropteropus pusillus and the aba roundleaf bat Hipposideros abae, which are believed to be reservoirs for the virus11


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 hosts interferon IFNs antiviral response12 IFNs are essential in order for the immune system to fight off viral infections in a host13 This inhibitory mechanism is believed to be due to a number of reasons, the first being, competitive inhibition of the formation of the transcription factor12 On this transcription factor, NSs interacts with and binds to a subunit that is needed for RNA polymerase I and II1214 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 response1214 Transcription suppression is believed to be another mechanism of this inhibitory process12 This occurs when an area of NSs interacts with and binds to the host’s protein, SAP30 and forms a complex1214 This complex causes histone acetylation to regress, which is needed for transcriptional activation of the IFN promoter14 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 hosts DNA, NSs forms a filamentous structure in the nucleus This allows the virus to interact with specific areas of the hosts DNA that relates to segregation defects and induction of chromosome continuity This increases host infectivity and decreases the host’s antiviral response12


Diagnosis relies on viral isolation from tissues, or serological testing with an ELISA3 Other methods of diagnosis include Nucleic Acid Testing NAT, cell culture, and IgM antibody assays15 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 methods16


A vaccine has been conditionally approved for use in animals in the US17 It has been shown that knockout of the NSs and NSm nonstructural proteins of this virus produces an effective vaccine in sheep as well18


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 In Egypt in 1977–78, an estimated 200,000 people were infected and there were at least 594 deaths19 20 In Kenya in 1998, the virus killed over 400 Kenyans In September 2000, an outbreak was confirmed in Saudi Arabia and Yemen On 19 October 2011, a case of Rift Valley fever contracted in Zimbabwe was reported in a Caucasian female traveler who returned to France after a 26-day stay in Marondera, Mashonaland East Province during July and August, 201121 but later classified as "not confirmed"22


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 This leads to an increase in mosquito vectors and is seen for a number of reasons23 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 is able to remain viable for a number of years in the egg Mosquitos lay their eggs in water, where they eventually hatch Since water is essential for mosquito eggs to hatch, it can be understood why rainfall and flooding cause an increase in the mosquito population, and in turn, an increased potential for the virus24

2006/07 outbreak in Kenya and Somaliaedit

In November 2006, a Rift Valley fever outbreak occurred in Kenya The victims are from the North Eastern Province and Coast Province of Kenya, which had received heavy rain in recent months, causing floods and creating breeding grounds for mosquitoes, which spread the virus of the fever from infected livestock to humans

By 7 January 2007, about 75 people had died and another 183 were infected25 The outbreak forced the closure of livestock markets in the North Eastern Province, affecting the economy of the region26

The outbreak was subsequently reported to have moved into Maragua and Kirinyaga districts of Central Province of Kenya27

On 20 January 2007, the outbreak was reported to have crossed into Somalia from Kenya and killed 14 people in the Lower Jubba region28

As of 23 January 2007, cases had started to crop up at the Kenyan capital, Nairobi Businesses were suffering large losses, as customers were shunning the common meat joints for the popular nyama choma roast meat, as it was believed to be spreading the fever

In December 2006 and again in January 2007, Taiwan International Health Action Taiwan IHA began operating missions in Kenya 29 consisting of medical experts assisting in training laboratory and health facility personnel, and included donations of supplies, such as mosquito sprays The United States Centers for Disease Control also set up an assistance mission and laboratory in Kenya

By the end of January, 2007, some 148 people had died since the outbreak began in December

As at 14 March 2007, the Kenyan government declared RVF as having diminished drastically after spending an estimated 25 million clarification needed in vaccine and deployment costs It also lifted the ban on cattle movement in the affected areas

As of 2 November 2007, 125 cases, including 60 deaths, had been reported from more than 10 localities of White Nile, Sinnar, and Gezira states in Sudan Young adult males are predominantly affected More than 25 human samples have been found positive for RVF by PCR or ELISA30

2010 South Africa outbreakedit

As of 8 April 2010, the Ministry of Health South Africa had reported 87 human cases infected with Rift Valley fever RVF, including two deaths in Free State, Eastern Cape and Northern Cape provinces31 Most of these cases reported direct contact with RVFV-infected livestock and or were linked to farms with confirmed animal cases of RVF The human cases are: farmers, veterinarians and farm workers All cases were confirmed with RVF by test conducted at the National Institute of Communicable Diseases NICD in Johannesburg, South Africa

An ongoing outbreak of Rift Valley fever virus RVFV infection is affecting sheep, goats, cattle and wildlife on farms within Free State, Eastern Cape, Northern Cape, Western Cape, Mpumalanga, North West, and Gauteng provinces As of 29 March 2010, about 78 farms reported laboratory-confirmed animal cases, with extensive livestock deaths

Outbreak investigations by the Department of Health and the Department of Agriculture, Forestry and Fisheries are ongoing, and are being supported by the South African Field Epidemiology and Training Programme and NICD The Department of Health and the Department of Agriculture are taking measures to enhance disease surveillance among cattle and in managing the control of the disease outbreak

Sporadic cases of RVFV infection in animals have been documented in South Africa in recent years The last major outbreak of the disease in humans occurred between 1974 and 1976, where an estimated 10,000 to 20,000 cases were recorded32

The disease claimed the life of Springbok rugby player Juan Smith's father Giel33

Biological weaponedit

Rift Valley fever was one of more than a dozen agents that the United States researched as potential biological weapons before the nation suspended its biological weapons program in 1969 due to possible bomb threats that might cause a panic in the United States3435


The disease is one of several identified by WHO as a likely cause of a future epidemic in a new plan developed after the Ebola epidemic for urgent research and development toward new diagnostic tests, vaccines and medicines3637


  1. ^ a b c d e f g h i j k l m "Rift Valley fever" Fact sheet N°207 World Health Organization May 2010 Retrieved 21 March 2014 
  2. ^ Palmer, S R 2011 Oxford textbook of zoonoses : biology, clinical practice, and public health control 2nd ed Oxford ua: Oxford Univ Press p 423 ISBN 9780198570028 
  3. ^ a b Rift Valley Fever reviewed and published by WikiVet, accessed 12 October 2011
  4. ^ Dessau M, Modis Y January 2013 "Crystal structure of glycoprotein C from Rift Valley fever virus" Proc Natl Acad Sci USA 110 5: 1696–701 PMC 3562824  PMID 23319635 doi:101073/pnas1217780110 
  5. ^ "ViralZone: Phlebovirus" viralzoneexpasyorg Retrieved 2016-09-14 
  6. ^ Jup, P G; Kemp, A; Grobbelaar, A; Lema, P; Burt, F J; Alahmed, A M; Al Mujalli, D; Al Khamees, M; Swanepoel, R 2002 "The 2000 epidemic of Rift Valley fever in Saudi Arabia: Mosquito vector studies" Medical and veterinary entomology 16 3: 245–252 PMID 12243225 doi:101046/j1365-2915200200371x 
  7. ^ Turell, M J; Presley, S M; Gad, A M; Cope, S E; Dohm, D J; Morrill, J C; Arthur, R R 1996 "Vector competence of Egyptian mosquitoes for Rift Valley fever virus" The American journal of tropical medicine and hygiene 54 2: 136–139 PMID 8619436 
  8. ^ Turell, M J; Lee, J S; Richardson, J H; Sang, R C; Kioko, E N; Agawo, M O; Pecor, J; O'Guinn, M L 2007 "Vector competence of Kenyan Culex zombaensis and Culex quinquefasciatus mosquitoes for Rift Valley fever virus" Journal of the American Mosquito Control Association 23 4: 378–382 PMID 18240513 doi:102987/56451 
  9. ^ Fontenille, D 1998 "New Vectors of Rift Valley Fever in West Africa" Emerging Infectious Diseases 4 2: 289–293 PMC 2640145  PMID 9621201 doi:103201/eid0402980218 
  10. ^ Swanepoel, R; Coetzer, JA 2004 "Rift Valley fever" In Coetzer, JA; Tustin, RC Infectious diseases of livestock 2nd ed Cape Town: Oxford University Press Southern Africa pp 1037–70 ISBN 0195761707 
  11. ^ Boiro, I; Konstaninov, O K; Numerov, A D 1987 "Isolation of Rift Valley Fever Virus from Bats in the Republic of Guinea" Bulletin de la Société de Pathologie Exotique et de ses Filiales in French 80 1: 62–68 PMID 3607999 
  12. ^ a b c d e f g Boshra, Hani; Lorenzo, Gema; Busquets, Núria; Brun, Alejandro 2011-07-01 "Rift Valley Fever: Recent Insights into Pathogenesis and Prevention" Journal of Virology 85 13: 6098–6105 ISSN 0022-538X PMC 3126526  PMID 21450816 doi:101128/JVI02641-10 
  13. ^ Fensterl, Volker; Sen, Ganes C 2009-01-01 "Interferons and viral infections" BioFactors 35 1: 14–20 ISSN 1872-8081 PMID 19319841 doi:101002/biof6 
  14. ^ a b c d Ikegami, Tetsuro; Makino, Shinji 2011-05-06 "The Pathogenesis of Rift Valley Fever" Viruses 3 5: 493–519 ISSN 1999-4915 PMC 3111045  PMID 21666766 doi:103390/v3050493 
  15. ^ Knipe, Howley, David, Peter 2013 Fields Virology, 6th Edition Philadelphia, PA, USA: LIPPINCOTT WILLIAMS & WILKINS, a WOLTERS KLUWER p 441 ISBN 978-1-4511-0563-6 
  16. ^ "Kemri develops kit for rapid test of viral disease" Retrieved 2016-09-14 
  17. ^ Ikegami, T; Hill, TE; Smith, JK; Zhang, L; Juelich, TL; Gong, B; Slack, OA; Ly, HJ; Lokugamage, N; Freiberg, AN 6 May 2015 "Rift Valley fever virus MP-12 vaccine is fully attenuated by a combination of partial attenuations in the S-, M- and L-segments" Journal of Virology 89 14: 7262–76 PMC 4473576  PMID 25948740 doi:101128/JVI00135-15 
  18. ^ Bird, Brian H; Maartens, Louis H; Campbell, Shelley; Erasmus, Baltus J; Erickson, Bobbie R; Dodd, Kimberly A; Spiropoulou, Christina F; Cannon, Deborah; Drew, Clifton P 2011-12-01 "Rift Valley Fever Virus Vaccine Lacking the NSs and NSm Genes Is Safe, Nonteratogenic, and Confers Protection from Viremia, Pyrexia, and Abortion following Challenge in Adult and Pregnant Sheep ▿" Journal of Virology 85 24: 12901–12909 ISSN 0022-538X PMC 3233145  PMID 21976656 doi:101128/JVI06046-11 
  19. ^ Arzt, J; White, WR; Thomsen, BV; Brown, CC Jan 2010 "Agricultural diseases on the move early in the third millennium" Vet Pathol 47 1: 15–27 PMID 20080480 doi:101177/0300985809354350 
  20. ^ Bird BH, Ksiazek TG, Nichol ST, Maclachlan NJ April 2009 "Rift Valley fever virus" J Am Vet Med Assoc 234 7: 883–93 PMID 19335238 doi:102460/javma2347883 
  21. ^ Vesin G 19 October 2011 "Rift Valley Fever, human—France: ex Zimbabwe Mashonaland East first report" ProMED mail International Society for Infectious Diseases 201110203132 
  22. ^ Grandadam M, Malvy D 29 November 2011 "Rift Valley Fever, human—France: ex Zimbabwe Mashonaland East not" ProMED mail International Society for Infectious Diseases 201111293486 
  23. ^ Nanyingi, Mark; Munyua, Peninah; Kiama, Stephen G; Muchemi, Gerald M; Thumbi, Samuel M; Bitek, Austine O; Bett, Bernard; Muriithi, Reese M; Njenga, M Kariuki 2015-07-31 "A systematic review of Rift Valley Fever epidemiology 1931-2014" Infection Ecology & Epidemiology 5: 28024 ISSN 2000-8686 PMC 4522434  PMID 26234531 doi:103402/ieev528024 
  24. ^ "Rift Valley Fever | CDC" wwwcdcgov Retrieved 2016-12-01 
  25. ^ "At least 75 people die of Rift Valley Fever in Kenya" International Herald Tribune 7 January 2007 
  26. ^ "Kenya: Schools Disrupted As Deadly Fever Hits Incomes" IRIN 11 January 2007 
  27. ^ "Nairobi at risk of RVF infection" The Standard Kenya 22 January 2007 Archived from the original on October 7, 2007 
  28. ^ "14 die after Rift Valley Fever breaks out in southern Somalia" Shabelle Media Network, Somalia 20 January 2007 Archived from the original on 2007-09-30 
  29. ^ Issue Mofagovtw 2012-04-02 Retrieved on 2014-05-12
  30. ^ "Deadly fever spreads Kenya Panic" BBC 26 January 2007 
  31. ^ ProMED-mail ProMED-mail Retrieved on 2014-05-12
  32. ^ "Rift Valley fever in South Africa" WHO 
  33. ^ "Driven by desperation" SArugby 
  34. ^ "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
  35. ^ "Select Agents and Toxins" PDF USDA-APHIS and CDC: National Select Agent Registry 2011-09-19 
  36. ^ Kieny, Marie-Paule "After Ebola, a Blueprint Emerges to Jump-Start R&D" Scientific American Blog Network Retrieved 13 December 2016 
  37. ^ "LIST OF PATHOGENS" World Health Organization Retrieved 13 December 2016 

External linksedit

  • ICD-10: A924
  • ICD-9-CM: 0663
  • MeSH: D012295
  • DiseasesDB: 31094

  • CDC RVF Information Page
  • Rift Valley Fever disease card at OIE
  • "Rift Valley fever" Fact sheet N°207 World Health Organization May 2010 Retrieved 21 March 2014 
  • "Rift Valley fever virus" NCBI Taxonomy Browser 11588 

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