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==Distribution==
==Distribution==
RVF virus was first identified in 1831 in the Rift Valley in Kenya during an investigation on a sheep farm and has since spread throughout Sub Saharan Africa emerging into North Africa in the 1970’s. the outbreak in Egypt in 1977-78 is considered to be the largest outbreak with 200,000 human cases reported <ref> ''Imam, Z. E., Karamany R. El., Darwish, M.A.'' (1979) An epidemic of Rift Valley fever in Egypt 2. Isolation of the virus from animals Bull World Health Organ. 1979; 57(3): 441–443.</ref> . In September 2000 it was reported for the first time outside of Africa, in Saudi Arabia and Yemen, probably introduced through infected livestock or mosquitoes <ref name="who"> [http://www.who.int/mediacentre/factsheets/fs207/en/ WHO Rift Valley Fever] accessed June 23, 2013 </ref> . The increase in cases in South Africa may be due to the end of an inter epizootic period <ref name="efsa">[''EFSA Panel on Animal Health and Welfare (AHAW)''; Scientific Opinion on Rift Valley fever. EFSA Journal 2013;11(4):3180. [48 pp.] doi:10.2903/j.efsa.2013.3180.]</ref> . Outbreaks are frequently reported though there is no evidence that it has spread to previously uninfected countries in the last 10 years, though it is hard to monitor changes in disease occurrence due to the cyclical occurrence of epidemics <ref name="efsa"/>. Most recently RVF was reported in Mauritania in November 2012 <ref name="who"/> . A map detailing current outbreaks can be found [http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/rvf/rvfmap.htm here]
RVF virus was first identified in 1831 in the Rift Valley in Kenya during an investigation on a sheep farm and has since spread throughout Sub Saharan Africa emerging into North Africa in the 1970’s. the outbreak in Egypt in 1977-78 is considered to be the largest outbreak with 200,000 human cases reported <ref name="imam"> ''Imam, Z. E., Karamany R. El., Darwish, M.A.'' (1979) An epidemic of Rift Valley fever in Egypt 2. Isolation of the virus from animals Bull World Health Organ. 1979; 57(3): 441–443.</ref> . In September 2000 it was reported for the first time outside of Africa, in Saudi Arabia and Yemen, probably introduced through infected livestock or mosquitoes <ref name="who"> [http://www.who.int/mediacentre/factsheets/fs207/en/ WHO Rift Valley Fever] accessed June 23, 2013 </ref> . The increase in cases in South Africa may be due to the end of an inter epizootic period <ref name="efsa">[''EFSA Panel on Animal Health and Welfare (AHAW)''; Scientific Opinion on Rift Valley fever. EFSA Journal 2013;11(4):3180. [48 pp.] doi:10.2903/j.efsa.2013.3180.]</ref> . Outbreaks are frequently reported though there is no evidence that it has spread to previously uninfected countries in the last 10 years, though it is hard to monitor changes in disease occurrence due to the cyclical occurrence of epidemics <ref name="efsa"/>. Most recently RVF was reported in Mauritania in November 2012 <ref name="who"/> . A map detailing current outbreaks can be found [http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/rvf/rvfmap.htm here]
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A number of [[Culicidae |mosquito]] species (''Aedes'', ''Culex'', ''Mansonia'', ''Anopheles'') are implicated as vectors of RFV, the most important being ''Aedes'' and ''Culex'' ''spp''. They are responsible for both maintenance and amplification of RVF.
A number of [[Culicidae |mosquito]] species (''Aedes'', ''Culex'', ''Mansonia'', ''Anopheles'') are implicated as vectors of RFV, the most important being ''Aedes'' and ''Culex'' ''spp''. They are responsible for both maintenance and amplification of RVF.
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Age is an important factor in determining the severity of the disease, young stock are more susceptible – 90% of infected lambs die whereas in adult sheep mortality can be as low as <10% <ref name="who"/>. Small ruminants are also more susceptible. Pigs are resistant to low doses of RVF but high doses can cause viraemia <ref name="vaccine"/> .
Age is an important factor in determining the severity of the disease, young stock are more susceptible – 90% of infected lambs die whereas in adult sheep mortality can be as low as <10% <ref name="who"/>. Small ruminants are also more susceptible. Pigs are resistant to low doses of RVF but high doses can cause viraemia <ref name="vaccine"/> .
During an outbreak in Egypt RVF virus was also isolated from horses as well as camels <ref>''Imam, Z. E., Karamany R. El., Darwish, M.A.'' (1979) An epidemic of Rift Valley fever in Egypt 2. Isolation of the virus from animals Bull World Health Organ. 1979; 57(3): 441–443.</ref>.
During an outbreak in Egypt RVF virus was also isolated from horses as well as camels <ref name="imam"/>.
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Other species (e.g. dogs and cats) have been infected experimentally and have become viraemic. The only species that are resistant are reptiles, birds and amphibians <ref name="oie" />.
Other species (e.g. dogs and cats) have been infected experimentally and have become viraemic. The only species that are resistant are reptiles, birds and amphibians <ref name="oie" />.