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       Rift Valley Fever is a Phlebovirus in the family Bunyaviridae that usually affects animals but can also infect humans.  Most human infections result from contact with the blood or organs of infected animals.  Human infections have also resulted from the bites of infected mosquitoes.  But as of 2017 no human-to-human transmission of the virus has been found.


       The length of time it takes from infection for symptoms to show varies from 2-6 days.  Outbreaks in animals may be prevented through animal vaccination.  Infection can cause severe disease in both animals and humans. The disease also results in significant economic losses due to death and abortion in livestock.


       The virus was first identified in 1931 on sheep on a farm in the Rift Valley of Kenya. Since then, outbreaks have been reported in sub-Saharan Africa. In 1977 a serious outbreak was reported in Egypt after the virus was introduced to Egypt via infected livestock along the Nile irrigation system. In 1997–98, a major outbreak occurred in Kenya, Somalia and Tanzania following an El Niño event and extensive flooding. Following infected livestock trade from the horn of Africa, the virus spread in September 2000 to Saudi Arabia and Yemen, marking the first reported occurrence of the disease outside the African continent and raising concerns that it could extend to other parts of Asia and Europe.




       The World Health Organization reported that most human infections result from direct or indirect contact with the blood or organs of infected animals. The virus can be transmitted to humans through the handling of animal tissue during slaughtering or butchering, assisting with animal births, conducting veterinary procedures, or from the disposal of carcasses or fetuses. People that work as herders, farmers, in slaughterhouse, and veterinarians are at high risk of infection. The virus also can infect humans through inoculation, as via a wound from an infected knife or through contact with broken skin, or through inhalation of aerosols produced during the slaughter of infected animals.  There is some evidence that ingesting the unpasteurized or uncooked milk of infected animals may infect humans.


       Human infections have also resulted from the bites of infected Aedes and Culex mosquitoes, and by infected blood-feeding flies.  No human-to-human transmission has been documented as of 2017, and no transmission to health care workers when standard infection control precautions have been practiced. There has been no evidence of outbreaks in urban areas.




       A sustained programme of animal vaccination can prevent outbreaks of Rift Valley Fever in animals. Both modified live attenuated virus and inactivated virus vaccines have been developed, and only a single dose of the live vaccine is required to provide long-term immunity.  However, live vaccine may result in spontaneous abortion if given to pregnant animals. The inactivated virus vaccine does not have this side effect, but multiple doses are required for protection, which may pose an obstacle in endemic areas.


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 Key References:     <medvet.ref.htm>    <Hexapoda>


Arzt, J., W. R. White, B. V. Thomsen & C. C. Brown.  2010.  Agricultural diseases on the move early in the third millennium.  Vet. Pathol.

        47(1):  15-27.

Bird, B. H., T. G. Ksiazek, S. T. Nichol & N. J. MacLachlan.  2009.  Rift Valley fever virus.  J. Amer. Vet. Med. Assoc. 234(7):  883-893.

Boiro, I., O. K. Konstaninov & A. D. Numerov.  1987.  Isolation of Rift Valley Fever Virus from Bats in the Republic of Guinea.  Bull Societé

       Pathologie Exotique et de ses Filiales 80(1):  62-68.

Jup, P. G., A. Kemp, A. Grobbelaar, P. Lema, F. J. Burt, A. M. Alahmed, D. Al Mujalli, M. Al Khamees & R. Swanepoel.  2002.  The 2000

       epidemic of Rift Valley Fever in Saudi Arabia: Mosquito vector studies.  Medical & Veterinary Entomol. 16(3): 245-252.

Knipe, H. & P. David.  2013.  Fields Virology, 6th Edition.  Philadelphia, PA, USA. 441 p.

Matheson, R. 1950.  Medical Entomology.  Comstock Publ. Co, Inc.  610 p.

Legner, E. F.  1995.  Biological control of Diptera of medical and veterinary importance.  J. Vector Ecology 20(1): 59_120.

Legner, E. F.  2000.  Biological control of aquatic Diptera.  p. 847_870.  Contributions to a Manual of Palaearctic Diptera,

       Vol. 1, Science  Herald, Budapest.  978 p.

Palmer, S. R.  2011.  Oxford Textbook of Zoonoses: Biology, Clinical Practice & Public Health Control, 2nd ed.  Oxford Univ. Press

Service, M.  2008.  Medical Entomology For Students.  Cambridge Univ. Press.  289 p.

Swanepoel, R. & J. A. Coetzer.  2004.  Rift Valley fever.  IN:  Coetzer, J. A. & R. C. Tustin.  Infectious Diseases of Livestock (2nd ed.).

       Oxford Univ. Press Southern Africa, pp. 1037-1070.

Turell, M. J., S. M. Presley, A. M. Gad, S. E. Cope, D. J. Dohm, J. C. Morrill & R. R. Arthur.  1996.  Vector competence of Egyptian

       mosquitoes for Rift Valley Fever virus.  Amer. J. Trop. Medicine & Hygiene 54(2):  136-139.

Turell, M. J., J. S. Lee, J. H. Richardson, R. C. Sang, E. N. Kioko, M. O. Agawo, J. Pecor & M. L. O'Guinn.  2007.  Vector competence of

       Kenyan Culex zombaensis and Culex quinquefasciatus mosquitoes for Rift Valley fever virus.  J. Amer. Mosq. Contr. Assoc. 23(4):  378-382.

       WHO.  2010.  Rift Valley Fever.  Fact sheet #207, World Health Organization.