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==Introduction==
==Introduction==
Rift Valley Fever (RVF) is a viral zoonotic disease belonging to the family ''Bunyaviridae'' in the ''Phlebovirus'' genus, possessing a segmented negative sense RNA genome. The disease has an episodic occurrence remerging ever 5-25 years and is seasonal in its occurrence. The occurrence of non immune animal populations every 5-25years combined with the introduction of RVF (due to rainfall) accounts for the explosive cyclical nature of the disease. RVF primarily affects animals but can infect humans and has the capacity to cause severe disease in both.
Rift Valley Fever (RVF) is a viral zoonotic disease belonging to the family [[:Category:Bunyaviridae|''Bunyaviridae'']] in the ''Phlebovirus'' genus, possessing a segmented negative sense RNA genome. The disease has an episodic occurrence reemerging ever 5-25 years and is seasonal in its occurrence. The occurrence of non immune animal populations every 5-25years combined with the introduction of RVF (due to rainfall) accounts for the explosive cyclical nature of the disease. RVF primarily affects animals but can infect humans and has the capacity to cause severe disease in both.
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RVF has a wide economic impact due to livestock loss and trade restrictions as well as public health implications. It is a notifiable disease.
RVF has a wide economic impact due to livestock loss and trade restrictions as well as public health implications. It is a notifiable disease.
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. 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. The increase in cases in South Africa may be due to the end of an inter epizootic period. 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. Most recently RVF was reported in Mauritania in November 2012. 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. 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. The increase in cases in South Africa may be due to the end of an inter epizootic period. 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. Most recently RVF was reported in Mauritania in November 2012. 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 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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Mosquitoes can be infected via feeding on infected animals. Vertical transmission can also occur (particularly in ''Aedes spp''); female infected mosquitoes lay virus infected eggs leading to a new generation of infected mosquitoes. Vertical transmission is important in the survival of the virus as the eggs laid by the female can survive for many months in dry conditions, hatching after a period of rain and so increasing spread post rainfall leading to epizootics. Once animal infection has occurred mosquitoes are then responsible for amplifying infection. ''Aedes'' mosquito numbers decrease following rain but ''Culex'' tend to breed in more permanent water sites, hence the continuation of virus spread.
Mosquitoes can be infected via feeding on infected animals. Vertical transmission can also occur (particularly in ''Aedes spp''); female infected mosquitoes lay virus infected eggs leading to a new generation of infected mosquitoes. Vertical transmission is important in the survival of the virus as the eggs laid by the female can survive for many months in dry conditions, hatching after a period of rain and so increasing spread post rainfall leading to epizootics. Once animal infection has occurred mosquitoes are then responsible for amplifying infection. ''Aedes'' mosquito numbers decrease following rain but ''Culex'' tend to breed in more permanent water sites, hence the continuation of virus spread.