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[[File:Q fever.jpg|thumb|200px|right|Straw coloured exudate and extravasated blood in abdomen in sheep with Q fever]]

[[File:Q fever.jpg|thumb|200px|right|Straw coloured exudate and extravasated blood in abdomen in sheep with Q fever]]

Rift Valley Fever is a '''[[Viruses | viral]] disease''' caused by a bunyavirus.

Rift Valley Fever is a '''[[Viruses |viral]] disease''' caused by a bunyavirus. It infects cattle, sheep, goats, camels and people.

 

It infects cattle, sheep, goats, camels and people.

RVF causes significant '''economic losses in Africa''', both directly through its clinical cases and also as an obstruction to the improvement of breeding stock due to the susceptibility of most imported livestock breeds into endemic areas.

RVF causes significant '''economic losses in Africa''', both directly through its clinical cases and also as an obstruction to the improvement of breeding stock due to the susceptibility of most imported livestock breeds into endemic areas.

This disease is '''notifiable''' to the World Organisation for Animal Health [http://www.oie.int/ (OIE)]

This disease is '''notifiable''' to the World Organisation for Animal Health [http://www.oie.int/ (OIE)]

==Distribution==

==Distribution==

'''Africa'''

The virus is currently only present in '''Africa'''. Huge '''epizootics''' develop, affecting up to '''90%''' of a group, usually in '''5-15 year cycles.'''

RVF is transmitted by a wide range of '''[[Culicidae |mosquitoes]]''' including ''Anopheles spp.'' and ''Culex spp.'' and also ''[[Hyalomma spp.]]'' '''[[Ticks |ticks]]''' and the '''[[Stomoxys calcitrans |stable fly]]'''. Some trans-ovarial transmission is also thought to occur. Climate and weather play a huge role in the emergence and survival of these vectors and thus also in amplification of the virus. The [[Mosquitoes |mosquitoes]] require cloud cover and regular, significant precipitation.

 

RVF is transmitted by a wide range of '''[[Culicidae | mosquitoes]]''' including ''Anopheles spp.'' and ''Culex spp.'' and also ''[[Hyalomma spp.]]'' '''[[Ticks | ticks]]''' and the '''[[Stomoxys calcitrans |stable fly]]'''. Some trans-ovarial transmission is also thought to occur. Climate and weather play a huge role in the emergence and survival of these vectors and thus also in amplification of the virus. The [[Mosquitoes | mosquitoes]] require cloud cover and regular, significant precipitation.

The disease follows the '''rainy season''' in most countries.

The disease follows the '''rainy season''' in most countries.

==Signalment==

==Signalment==

'''Cattle, sheep, goats and humans''' are important hosts. This is due in part to their presence in huge numbers in epizootic areas and therefore ability to greatly '''amplify viral presence''' in a population and transmit to others and humans.

'''Cattle, sheep, goats and humans''' are important hosts. This is due in part to their presence in huge numbers in epizootic areas and therefore ability to greatly '''amplify viral presence''' in a population and transmit to others.

''Bos Taurus'' cattle and other European breed imported into Africa appear highly susceptible to RVF.

''Bos Taurus'' cattle and other European breed imported into Africa appear highly susceptible to RVF. '''Indigenous breeds''' appear to be '''resistant''' to disease, as do pigs.

 

'''Indigenous breeds''' appear to be '''resistant''' to disease, as do pigs.

Cats, dogs, rats and other rodents seem to be accidental hosts infected by mosquitoes.

Cats, dogs, rats and other rodents seem to be accidental hosts infected by mosquitoes.

==Clinical Signs==

==Clinical Signs==

'''Abortions''' occurring in huge '''storms''' with '''high mortality''' in both neonates and adults are characteristic of disease. Agalactia may also develop.

'''Abortions''' occurring in huge '''storms''' with '''high mortality''' in both neonates and adults are characteristic of the disease. Agalactia may also develop.

'''[[Vomiting]] and [[Diarrhoea | diarrhoea]]'''may involve melaena and haematochezia.

'''[[Vomiting]] and [[Diarrhoea |diarrhoea]] '''may involve melaena and haematochezia.

'''Tachycardia, cyanosis''', petechiation, haemorrhage and clotting defects are haematological consequences of RVF.

'''Tachycardia, cyanosis''', petechiation, haemorrhage and clotting defects are haematological consequences of RVF.

The respiratory disease of RVF is non-specific: Purulent nasal discharge, epistaxis, tachypnoea and dyspnoea.

The respiratory disease of RVF is non-specific: Purulent nasal discharge, epistaxis, tachypnoea and dyspnoea.

Fever, lymphadenopathy, depression and lethargy usually accompany infection.

Fever, lymphadenopathy, depression and lethargy usually accompany infection. Hepatitis may cause consequent [[photosensitisation]].  

 

Hepatitis may cause consequent photosensitisation.  

In young animals, '''peracute disease''' causes anorexia, listlessness, collapse and death.

In young animals, '''peracute disease''' causes anorexia, listlessness, collapse and death.

==Diagnosis==

==Diagnosis==

Sudden onset of acute debilitating disease in man and abortion/neonatal death in domestic animals should raise suspicion in appropriate countries.  

Sudden onset of acute debilitating disease in man and abortion/neonatal death in domestic animals should raise suspicion in the appropriate countries.  

'''Viral isolation''' can be performed from '''placenta, foetal liver''' and other tissues.

'''Viral isolation''' can be performed from '''placenta, foetal liver''' and other tissues.

The virus can also be innoculated into tissue cultures and diagnosed by Fluorescent Antibody Testing '''(FAT)''' or '''immune-peroxidase''' staining.  

The virus can also be innoculated into tissue cultures and diagnosed by [[FAT|Fluorescent Antibody Testing '''(FAT)''']] or '''immune-peroxidase''' staining.  

Fixed liver samples can be '''immunostained''',and sera from aborted animals examined to confirm viral presence and are both simple and sensitive.  

Fixed liver samples can be '''immunostained''' and sera from aborted animals examined to confirm viral presence and are both simple and sensitive.  

'''IgM [[ELISA testing | ELISA]]''' can also be performed on serum.

'''IgM [[ELISA testing |ELISA]]''' can also be performed on serum.

On '''necropsy''', in the viraemic stage, widespread '''petechiae and ecchymoses''' on serous surfaces and organs will be seen and '''extravasated blood''' present in the body cavities.  

On '''necropsy''', in the viraemic stage, widespread '''petechiae and ecchymoses''' on serous surfaces and organs will be seen and '''extravasated blood''' present in the body cavities.  

==Control==

==Control==

Modified live and inactivated '''vaccines''' are available. Live vaccination is only recommended in '''non-pregnant''' animals due to its ability to cause abortion and neurological deficits in lambs. In epizootic situations though, this risk may well be worth taking.  

Modified live and inactivated '''[[vaccines]]''' are available. Live vaccination is only recommended in '''non-pregnant''' animals due to its ability to cause abortion and neurological deficits in lambs. In epizootic situations though, this risk may well be worth taking.  

Inactivated vaccines are ineffective during epizootics and therefore less widely used than modified live strains.

Inactivated vaccines are ineffective during epizootics and therefore less widely used than modified live strains.

Mosquito and larval control is extremely valuable. Slow release '''larvicides''' such as '''methoprene''' can be applied to well defined mosquito breeding areas.

Mosquito and larval control is extremely valuable. Slow release '''larvicides''' such as '''methoprene''' can be applied to well-defined mosquito breeding areas.

Sentinel cattle are used for epidemiological surveillance, and are tested 2-3months after the seasonal rains.

Sentinel cattle are used for epidemiological surveillance, and are tested 2-3months after the seasonal rains.

{{Learning

{{Learning

|flashcards = [[Rift Valley Fever Flashcards]]

|flashcards = [[Rift Valley Fever Flashcards]]

}}

}}

==References==

==References==

Animal Health & ProductIon Compendium, '''Rift Valley Fever Virus datasheet''', accessed 08/06/2011 @ http://www.cabi.org/ahpc/

Animal Health & ProductIon Compendium, '''Rift Valley Fever Virus datasheet''', accessed 08/06/2011 @ http://www.cabi.org/ahpc/

[[Category:To Do - CABI review]]

 

[[Category:To Do - Steph]]