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→Diagnosis
==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 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]
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"/>. See a [http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/rvf/rvfmap.htm map detailing current outbreaks].
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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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RVF causes severe disease in animals, mainly cattle, sheep, goats and camels, with sheep being more susceptible. ''Bos Taurus'' cattle and other European breed imported into Africa appear highly susceptible to RVF.
RVF causes severe disease in animals, mainly cattle, sheep, goats and camels, with sheep being more susceptible. ''Bos Taurus'' cattle and other European breed imported into Africa appear highly susceptible to 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 name="imam"/>.
During an outbreak in Egypt RVF virus was also isolated from horses as well as camels <ref name="imam"/>.
RVF has an incubation period of 1-6 days (12-36 hrs in lambs).<ref name="oie" /> Once in the lymph nodes viral replication occurs which leads to viraemia and systemic infection. Spontaneous abortions are seen as the hallmark of RVF outbreaks.<ref name="who"/> Pregnant animals can abort at any stage often with 100% of stock aborting.<ref name="vaccine"/>
RVF has an incubation period of 1-6 days (12-36 hrs in lambs).<ref name="oie" /> Once in the lymph nodes viral replication occurs which leads to viraemia and systemic infection. Spontaneous abortions are seen as the hallmark of RVF outbreaks.<ref name="who"/> Pregnant animals can abort at any stage often with 100% of stock aborting.<ref name="vaccine"/>
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Newborn lambs and kids are highly susceptible to RVF, presenting with pyrexia and anorexia shortly followed by death 24-36hrs after infection.<ref name="vaccine"/> <ref name="fao"> [http://www.fao.org/docrep/006/y4611e/y4611e00.htm#Contents FAO Recognising Rift Valley Fever]accessed June 23, 2013</ref> In newborn lambs hepatocytes of the liver are the predominant target cell with hepatic necrosis being a significant post mortem finding. Other organs affected include the gall bladder (haemorrhage and oedema), gastrointestinal tract haemorrhage, lymph node haemorrhage, cutaneous haemorrhage and haemothorax.<ref name="fao"/> <ref name="oie" />
Newborn lambs and kids are highly susceptible to RVF, presenting with pyrexia and anorexia shortly followed by death 24-36hrs after infection.<ref name="vaccine"/> <ref name="fao"> [http://www.fao.org/docrep/006/y4611e/y4611e00.htm#Contents FAO Recognising Rift Valley Fever] accessed June 23, 2013</ref> In newborn lambs hepatocytes of the liver are the predominant target cell with hepatic necrosis being a significant post mortem finding. Other organs affected include the gall bladder (haemorrhage and oedema), gastrointestinal tract haemorrhage, lymph node haemorrhage, cutaneous haemorrhage and haemothorax.<ref name="fao"/> <ref name="oie" />
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Signs in older lambs, kids, calves and adults vary from acute to subclinical (20-70% mortality), Signs can include fever (lasts 24-96hrs), weakness, bloody diarrhoea, abdominal pain, photosensitivity, anorexia, excessive salivation and decreased milk production. Signs in adult cattle are most often subclinical with less than 10% mortality.<ref name="oie" /> <ref name="fao"/> <ref name="vaccine"/>
Signs in older lambs, kids, calves and adults vary from acute to subclinical (20-70% mortality), Signs can include fever (lasts 24-96hrs), weakness, bloody diarrhoea, abdominal pain, photosensitivity, anorexia, excessive salivation and decreased milk production. Signs in adult cattle are most often subclinical with less than 10% mortality.<ref name="oie" /> <ref name="fao"/> <ref name="vaccine"/>
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Camels display signs similar to those seem with Pasteurellosis infection, though infection can also be subclinical or asymptomatic. Abortions can also occur. During the 2010 outbreak in Mauritania 2 forms of disease were observed in camels; a hyperacute form causing sudden death in <24hrs and an acute form causing fever, ataxia, respiratory signs, icterus, oedema, foot lesions and neurological signs. If haemorrhagic signs were observed death occurred in a few days.<ref> ''Ahmed B. Ould El Mamy, Mohamed Ould Baba, Yahya Barry, Katia Isselmou, Mamadou L. Dia,
Camels display signs similar to those seen with Pasteurellosis infection, though infection can also be subclinical or asymptomatic. Abortions can also occur. During the 2010 outbreak in Mauritania 2 forms of disease were observed in camels; a hyperacute form causing sudden death in <24hrs and an acute form causing fever, ataxia, respiratory signs, [[icterus]], oedema, foot lesions and neurological signs. If haemorrhagic signs were observed death occurred in a few days.<ref> ''Ahmed B. Ould El Mamy, Mohamed Ould Baba, Yahya Barry, Katia Isselmou, Mamadou L. Dia,
Ba Hampate, Mamadou Y. Diallo, Mohamed Ould Brahim El Kory, Mariam Diop, Modou Moustapha Lo, Yaya Thiongane, Mohammed Bengoumi, Lilian Puech, Ludovic Plee, Filip Claes,Stephane de La Rocque, and Baba Doumbia,'' (2011) Unexpected Rift Valley Fever Outbreak, Northen Mauritania, Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 17, No. 10, October 2011 </ref>
Ba Hampate, Mamadou Y. Diallo, Mohamed Ould Brahim El Kory, Mariam Diop, Modou Moustapha Lo, Yaya Thiongane, Mohammed Bengoumi, Lilian Puech, Ludovic Plee, Filip Claes,Stephane de La Rocque, and Baba Doumbia,'' (2011) Unexpected Rift Valley Fever Outbreak, Northen Mauritania, Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 17, No. 10, October 2011 </ref>
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Differential diagnosis should include: bluetongue, Wesselbron disease, Enterotoxaemia of sheep, Ephemeral fever, Brucellosis, Vibrosis, Trichomonosis, Nairobi sheep disease, Heartwater, Ovine enzootic abortion, plant toxicity, bacterial septicaemias, Rinderpest, Anthrax.<ref name="oie" />
Differential diagnosis should include: [[Bluetongue Virus|bluetongue]], Wesselbron disease, Enterotoxaemia of sheep, [[Ephemeral Fever|Ephemeral fever]], [[Bovine Brucellosis|Brucellosis]], Vibrosis, [[Trichomonosis - Cattle|Trichomonosis]], Nairobi sheep disease, [[Heartwater]], [[Enzootic Abortion of Ewes|Ovine enzootic abortion]], plant toxicity, bacterial septicaemias, [[Rinderpest]], [[Anthrax]].<ref name="oie" />
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Humans develop '''malarial-like''' disease. High risk individuals include farmers, veterinarians and abattoir staff. Mild disease is most common but severe hepatitis, encephalitis and ocular damage can develop. The usual presentation is of sudden onset fever, myalgia, biphasic behaviour and gastrointestinal disease.<ref name="who"/>
Humans develop '''malarial-like''' disease. High risk individuals include farmers, veterinarians and abattoir staff. Mild disease is most common but severe hepatitis, encephalitis and ocular damage can develop. The usual presentation is of sudden onset fever, myalgia, biphasic behaviour and gastrointestinal disease.<ref name="who"/>
The nucleocapsid protein is used as the antigen of choice in serological assays. Blood samples can be used to detect the virus during the early phase using virus propagation, antigen detection and RT-PCR.
The nucleocapsid protein is used as the antigen of choice in serological assays. Blood samples can be used to detect the virus during the early phase using virus propagation, antigen detection and RT-PCR.
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During the acute stages ELISA or EIA can be used to confirm the presence of IgM antibody to the virus, which allows recent infections to be diagnosed. ELISA’s based on recombinant RVF virus proteins have been developed which negates the need for biosecure facilities and are used in a number of species.<ref name="vaccine"/>.Cross reactions may occur with other ''phleboviruses''<ref name="vaccine"/>
During the acute stages '''[[ELISA]]''' or '''EIA''' can be used to confirm the presence of IgM antibody to the virus, which allows recent infections to be diagnosed. ELISA’s based on recombinant RVF virus proteins have been developed which negates the need for biosecure facilities and are used in a number of species.<ref name="vaccine"/>.Cross reactions may occur with other ''phleboviruses''<ref name="vaccine"/>
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RT-PCR is the standard method used in most laboratories as it has a high sensitivity. This is useful for rapid diagnosis and can also be used to detect RVF virus in mosquito pools.<ref name="oie" />
'''RT-[[PCR]]''' is the standard method used in most laboratories as it has a high sensitivity. This is useful for rapid diagnosis and can also be used to detect RVF virus in mosquito pools.<ref name="oie" />
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Virus neutralisation tests (VNT) are very specific and sensitive and can be performed in a biosecure laboratory. They are also the prescribed test for international trade, though it cannot differentiate between vaccinated and infected animals.<ref name="oie" /> It is the only method to detect functional antibodies though a low level of cross reaction to some other ''phleboviruses'' has been observed.<ref name="vaccine"/> Plaque reduction neutralisation assays are the most commonly used VNTs and involve incubating the virus and heat inactivated serum allowing the virus to infect. 4-6 days later the presence of cytopathic plaques is observed.
'''Virus neutralisation tests '''(VNT) are very specific and sensitive and can be performed in a biosecure laboratory. They are also the prescribed test for international trade, though it cannot differentiate between vaccinated and infected animals.<ref name="oie" /> It is the only method to detect functional antibodies though a low level of cross reaction to some other ''phleboviruses'' has been observed.<ref name="vaccine"/> Plaque reduction neutralisation assays are the most commonly used VNTs and involve incubating the virus and heat inactivated serum allowing the virus to infect. Four to six days later the presence of cytopathic plaques is observed.
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Haemagglutination inhibition (HI) and complement fixation assays are available but show extensive cross reactivity with other ''phlebovirus'' species.<ref name="vaccine"/> HI assays are used in non endemic areas but animals previously infected with other ''phleboviruses'' may show a positive result.<ref name="oie" /> Immunofluorescence can also be used.
'''[[Agglutination|Haemagglutination inhibition]]''' (HI) and complement fixation assays are available but show extensive cross reactivity with other ''phlebovirus'' species.<ref name="vaccine"/> HI assays are used in non endemic areas but animals previously infected with other ''phleboviruses'' may show a positive result.<ref name="oie" /> '''[[Immunofluorescence]]''' can also be used.
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Definitive confirmation can be carried out by virus isolation, however due to the zoonotic risk this can only be carried out in biosecure facilities.<ref name="oie" />
Definitive confirmation can be carried out by '''virus isolation''', however due to the zoonotic risk this can only be carried out in biosecure facilities.<ref name="oie" />
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Histopathology on tissue samples will show cytopathology and immunostaining can be used to identify RVF antigen in cells. On post mortem during the viraemic stage, widespread petechiae and ecchymoses on serous surfaces and organs will be seen and present in the body cavities. In older animals, the liver is enlarged and inflamed, with many foci of necrosis which are bronzed and jaundiced. The gall bladder may also be distended and haemorrhagic. Lymph nodes are enlarged and their germinal centres may be necrotic on closer examination. Extensive subcapsular haemorrhage in the spleen is usual. Renal changes include oedema and congestion. Epicardial and endocardial haemorrhages are often present on the heart.<ref>[http://www.fao.org/docrep/006/Y4611E/y4611e05.htm FAO Signs of Rift Valley Fever] accessed June 23, 2013</ref>
'''Histopathology''' on tissue samples will show cytopathology and immunostaining can be used to identify RVF antigen in cells. On post mortem during the viraemic stage, widespread petechiae and ecchymoses on serous surfaces and organs will be seen and present in the body cavities. In older animals, the liver is enlarged and inflamed, with many foci of necrosis which are bronzed and jaundiced. The gall bladder may also be distended and haemorrhagic. Lymph nodes are enlarged and their germinal centres may be necrotic on closer examination. Extensive subcapsular haemorrhage in the spleen is usual. Renal changes include oedema and congestion. Epicardial and endocardial haemorrhages are often present on the heart.<ref>[http://www.fao.org/docrep/006/Y4611E/y4611e05.htm FAO Signs of Rift Valley Fever] accessed June 23, 2013</ref>
==Treatment==
==Treatment==