Changes

==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> http://www.who.int/mediacentre/factsheets/fs207/en/ </ref> . The increase in cases in South Africa may be due to the end of an inter epizootic period <ref>''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> ''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>. Most recently RVF was reported in Mauritania in November 2012 <ref> http://www.who.int/mediacentre/factsheets/fs207/en/</ref> . 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> ''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>''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> ''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>. 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]  

<br><br>

<br><br>

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.

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.  

<br><br

<br><br

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> http://www.who.int/mediacentre/factsheets/fs207/en/</ref>. Small ruminants are also more susceptible. Pigs are resistant to low doses of RVF but high doses can cause viraemia <ref>''Lagerqvist, N,'' Rift Valley fever virus vaccine strategies, Karolinska Institutet 2013 </ref> .  

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>''Lagerqvist, N,'' Rift Valley fever virus vaccine strategies, Karolinska Institutet 2013 </ref> .  

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>''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>.

<br><br>

<br><br>

==Clinical Signs==

==Clinical Signs==

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>http://www.who.int/mediacentre/factsheets/fs207/en/</ref> Pregnant animals can abort at any stage often with 100% of stock aborting.<ref> ''Lagerqvist, N'', Rift Valley fever virus vaccine strategies, Karolinska Institutet 2013 </ref>   

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> ''Lagerqvist, N'', Rift Valley fever virus vaccine strategies, Karolinska Institutet 2013 </ref>   

<br><br>

<br><br>

Newborn lambs and kids are highly susceptible to RVF, presenting with pyrexia and anorexia shortly followed by death 24-36hrs after infection.<ref>''Lagerqvist, N'', Rift Valley fever virus vaccine strategies, Karolinska Institutet 2013</ref> <ref> http://www.fao.org/docrep/006/y4611e/y4611e00.htm#Contents</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>http://www.fao.org/docrep/006/y4611e/y4611e00.htm#Contents</ref> <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>''Lagerqvist, N'', Rift Valley fever virus vaccine strategies, Karolinska Institutet 2013</ref> <ref> http://www.fao.org/docrep/006/y4611e/y4611e00.htm#Contents</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>http://www.fao.org/docrep/006/y4611e/y4611e00.htm#Contents</ref> <ref name="oie" />  

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, 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" />

<br><br>

<br><br>

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>http://www.who.int/mediacentre/factsheets/fs207/en/</ref>

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"/>

==Diagnosis==

==Diagnosis==

During an outbreak, control at slaughterhouses to reduce zoonotic spread. Contact with animals, both direct and indirect, should be avoided. Movement restrictions should be enforced to prevent movement of the disease from diseased areas to RVF free areas; however movement restrictions within endemic countries have had little impact on the spread of RVF.<ref> http://www.fao.org/docrep/006/y4611e/y4611e00.htm#Contents</ref>

During an outbreak, control at slaughterhouses to reduce zoonotic spread. Contact with animals, both direct and indirect, should be avoided. Movement restrictions should be enforced to prevent movement of the disease from diseased areas to RVF free areas; however movement restrictions within endemic countries have had little impact on the spread of RVF.<ref> http://www.fao.org/docrep/006/y4611e/y4611e00.htm#Contents</ref>

<br><br>  

<br><br>  

Forecasting is key as outbreaks occur following a period of heavy rain, thus is rain is forecast preventative measures can be implemented beforehand to help prevent/ lessen the impact of an outbreak.<ref> http://www.who.int/mediacentre/factsheets/fs207/en/</ref>

Forecasting is key as outbreaks occur following a period of heavy rain, thus is rain is forecast preventative measures can be implemented beforehand to help prevent/ lessen the impact of an outbreak.<ref name="who"/>

<br><br>

<br><br>

Mosquito breeding sites should be reduced through drainage and larvicidal measures. Methoprene spraying, larvicidal toxins and controlled burning can be used, though low level aerial spraying has been shown to have little effect.<ref>http://www.fao.org/docrep/006/y4611e/y4611e00.htm#Contents</ref>

Mosquito breeding sites should be reduced through drainage and larvicidal measures. Methoprene spraying, larvicidal toxins and controlled burning can be used, though low level aerial spraying has been shown to have little effect.<ref>http://www.fao.org/docrep/006/y4611e/y4611e00.htm#Contents</ref>

The formalin inactivated virus vaccine (with Aluminium Hydroxide adjuvant) requires multiple doses to achieve immunity, and annual boosters are needed as it is less immunogenic.<ref> ''Lagerqvist N, Moiane B, Bucht G, Fafetine J, Paweska J.T., Lundkvist Å and Falk K.I.'' 2012. Stability of a formalin‐inactivated Rift Valley fever vaccine: evaluation of a vaccination campaign for cattle in Mozambique. Vaccine 30(46):6534‐40.</ref>It is safe to use in pregnant ewes. Biosecurity is also a consideration when using this vaccine as reversion to virulence is a possibility.

The formalin inactivated virus vaccine (with Aluminium Hydroxide adjuvant) requires multiple doses to achieve immunity, and annual boosters are needed as it is less immunogenic.<ref> ''Lagerqvist N, Moiane B, Bucht G, Fafetine J, Paweska J.T., Lundkvist Å and Falk K.I.'' 2012. Stability of a formalin‐inactivated Rift Valley fever vaccine: evaluation of a vaccination campaign for cattle in Mozambique. Vaccine 30(46):6534‐40.</ref>It is safe to use in pregnant ewes. Biosecurity is also a consideration when using this vaccine as reversion to virulence is a possibility.

<br><br>

<br><br>

Vaccines should be administered prior to outbreak to prevent an epizootic. Vaccination during an outbreak may worsen the situation, especially if multi dose vials are used, due to the possibility of viraemic animals being vaccinated and then the same vial being used on a healthy animal, thus spreading the virus.<ref>http://www.who.int/mediacentre/factsheets/fs207/en/</ref> The use of the Smithburn vaccine is restricted in non endemic areas and during outbreaks due to the possibility of reassortment and a return to virulence.  

Vaccines should be administered prior to outbreak to prevent an epizootic. Vaccination during an outbreak may worsen the situation, especially if multi dose vials are used, due to the possibility of viraemic animals being vaccinated and then the same vial being used on a healthy animal, thus spreading the virus.<ref name="who"/> The use of the Smithburn vaccine is restricted in non endemic areas and during outbreaks due to the possibility of reassortment and a return to virulence.  

<br><br>

<br><br>

More recently a naturally attenuated virus vaccine has been developed (Clone 13) that is marketed in South Africa and Namibia.<ref>''Kortekaas J, Zingeser J, de Leeuw P, de La Rocque S, Unger H, Moormann RJ.'',2011 Rift Valley Fever Vaccine Development, Progress and Constraints. Emerg Infect Dis. 2011 Sep;17(9)</ref><ref>http://www.rr-africa.oie.int/docspdf/en/2012/RVF/MBAO01.pdf</ref> Testing in pregnant ewes and lambs demonstrated safety and it has been shown to be as effective as the Smithburn vaccine in conferring immunity.<ref>''Dungu B, Louw I, Lubisi A, Hunter P, von Teichman BF, Bouloy M'' (2010). Evaluation of the efficacy and safety of the Rift Valley Fever Clone 13 vaccine in sheep.,  Vaccine. 2010 Jun 23;28(29):4581-7</ref> <ref>''von Teichman B, Engelbrecht A, Zulu G, Dungu B, Pardini A, Bouloy M'' (2011). Safety and efficacy of Rift Valley fever Smithburn and Clone 13 vaccines in calves. . Vaccine. 2011 Aug 5;29(34):5771-7</ref> The vaccine has however shown to cause neurological disease and paralysis in some vaccinated mice.<ref>''Vialat P., Billecocq A., Kohl A., and Bouloy M.'' (2000). The S segment of Rift Valley fever phlebovirus (Bunyaviridae) carries determinants for attenuation and virulence in mice. J Virol 74:1538‐1543.</ref>

More recently a naturally attenuated virus vaccine has been developed (Clone 13) that is marketed in South Africa and Namibia.<ref>''Kortekaas J, Zingeser J, de Leeuw P, de La Rocque S, Unger H, Moormann RJ.'',2011 Rift Valley Fever Vaccine Development, Progress and Constraints. Emerg Infect Dis. 2011 Sep;17(9)</ref><ref>http://www.rr-africa.oie.int/docspdf/en/2012/RVF/MBAO01.pdf</ref> Testing in pregnant ewes and lambs demonstrated safety and it has been shown to be as effective as the Smithburn vaccine in conferring immunity.<ref>''Dungu B, Louw I, Lubisi A, Hunter P, von Teichman BF, Bouloy M'' (2010). Evaluation of the efficacy and safety of the Rift Valley Fever Clone 13 vaccine in sheep.,  Vaccine. 2010 Jun 23;28(29):4581-7</ref> <ref>''von Teichman B, Engelbrecht A, Zulu G, Dungu B, Pardini A, Bouloy M'' (2011). Safety and efficacy of Rift Valley fever Smithburn and Clone 13 vaccines in calves. . Vaccine. 2011 Aug 5;29(34):5771-7</ref> The vaccine has however shown to cause neurological disease and paralysis in some vaccinated mice.<ref>''Vialat P., Billecocq A., Kohl A., and Bouloy M.'' (2000). The S segment of Rift Valley fever phlebovirus (Bunyaviridae) carries determinants for attenuation and virulence in mice. J Virol 74:1538‐1543.</ref>