Changes

==Diagnosis==

==Diagnosis==

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

Following infection viraemia is often high (though short lived) so the virus can be easily detected in the blood shortly after. Tissue samples can also be used in dead animals or aborted foetuses.

 

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

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

 

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. Cross reactions may occur with other ''phleboviruses''.

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

 

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.  

'''IgM [[ELISA testing |ELISA]]''' can also be performed on serum. Virus neutralisation is the prescribed test for international trading of animals <ref> OIE, 2009. http://www.oie.int/fileadmin/Home/eng/Animal_Health_in_the_World/docs/pdf/RIFT_VALLEY_FEVER_FINAL.pdf. Accessed 08/07/2012</ref>

 

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. It is the only method to detect functional antibodies though a low level of cross reaction to some other ''phleboviruses'' has been observed. 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.

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.  

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Haemagglutination inhibition (HI) and complement fixation assays are available but show extensive cross reactivity with other ''phlebovirus'' species. HI assays are used in non endemic areas but animals previously infected with other ''phleboviruses'' may show a positive result. Immunofluorescence can also be used.

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.

Definitive confirmation can be carried out by virus isolation, however due to the zoonotic risk this can only be carried out in biosecure facilities.

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.

==Treatment==

==Treatment==