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== Diagnosis ==

== Diagnosis ==

A manual on the diagnosis of PPR has been produced (FAO, 1998). Suspicion of PPR would be raised by signs of stomatitis – or pneumonitis, with enteritis in several animals. A high mortality and morbidity rate would be expected in outbreaks occurring in non-endemic areas, or where outbreaks have not occurred for some time and animals are not vaccinated.  

History, signalment and clinical signs may lead to a presumptive diagnosis of this countries in countries where it is endemic.

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Other conditions which need to be eliminated as differentials are rinderpest in small ruminants, contagious caprine pleuropneumonia, bluetongue, pasteurellosis, contagious ecthyma, foot-and-mouth disease, heartwater, coccidiosis and mineral poisoning. Rinderpest virus can cause disease in small ruminants, but where RP exists as a risk to small ruminants, disease in cattle would be expected, since many countries have ceased vaccination. Bluetongue infection occurs in many countries that are endemic or at-risk from PPR incursion. It can give rise to a muco-purulent discharge and high morbidity and mortality rate in susceptible sheep, but usually less so in goats. It does not usually result in a severe enteritis, although loose stools may occur, or erosions/ulcerations of epithelial surfaces. Bluetongue usually gives rise to visible signs of haemorrhage on the coronary band of the foot, in contrast to PPR. Foot-and-mouth disease affects other stock as well as sheep and goats; cattle in the region would be expected to show more severe signs than sheep or goats. On occasion though, the disease is more severe in the latter, and cattle may be absent. However, the enteritis usually present in PPR is not seen in FMD. The lesions of orf (contagious ecthyma) and sheep and goat pox differ in distribution to that of PPR, but animals recovering from PPR may develop proliferative growths on the lips resembling orf, and the virus may be involved in the pathogenesis of the condition. Contagious caprine pleuropneumonia occurs in many similar countries to PPR but does not usually give a high mortality in sheep, or have an accompanying severe enteritis. Heartwater can give a high mortality rate in susecptible breeds, but without a stomatitis.

Other conditions which need to be eliminated as differentials are rinderpest in small ruminants, contagious caprine pleuropneumonia, bluetongue, pasteurellosis, contagious ecthyma, foot-and-mouth disease, heartwater, coccidiosis and mineral poisoning.  

Rinderpest virus can cause disease in small ruminants, but where RP exists as a risk to small ruminants, disease in cattle would be expected, since many countries have ceased vaccination. Rinderpest has now been eradicated worldwide.

Bluetongue infection occurs in many countries that are endemic or at-risk from PPR incursion. It can give rise to a muco-purulent discharge and high morbidity and mortality rate in susceptible sheep, but usually less so in goats. It does not usually result in a severe enteritis, although loose stools may occur, or erosions/ulcerations of epithelial surfaces. Bluetongue usually gives rise to visible signs of haemorrhage on the coronary band of the foot, in contrast to PPR.  

Foot-and-mouth disease affects other stock as well as sheep and goats; cattle in the region would be expected to show more severe signs than sheep or goats. On occasion though, the disease is more severe in the latter, and cattle may be absent. However, the enteritis usually present in PPR is not seen in FMD.  

The lesions of orf (contagious ecthyma) and sheep and goat pox differ in distribution to that of PPR, but animals recovering from PPR may develop proliferative growths on the lips resembling orf, and the virus may be involved in the pathogenesis of the condition.  

Contagious caprine pleuropneumonia occurs in many similar countries to PPR but does not usually give a high mortality in sheep, or have an accompanying severe enteritis.  

Heartwater can give a high mortality rate in susecptible breeds, but without a stomatitis.

 

PPRV is present at a high concentration in secretions and tissue samples in the early stages of the disease, but rapidly becomes difficult to detect after development of antibody responses. Collection of specimens from animals which have a serous ocular-nasal discharge and fever is preferable compared to later-stage signs of necrotic stomatitis-enteritis. In live animals samples taken should include gum debris, conjunctival swabs, clotted blood and whole blood and tissues from post mortem. From the necropsy examination of two to three animals, lymph nodes, especially the mesenteric and bronchial nodes, lungs, spleen and intestinal mucosae should also be collected aseptically, chilled on ice and transported under refrigeration. Fragments of organs collected for histopathology are placed in 10% formalin.  

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PPRV is present at a high concentration in secretions and tissue samples in the early stages of the disease, but rapidly becomes difficult to detect after development of antibody responses. Collection of specimens from animals which have a serous ocular-nasal discharge and fever is preferable compared to later-stage signs of necrotic stomatitis-enteritis. In live animals, swabs should be made of the conjunctival discharges from the nasal and buccal mucosae. Whole blood should be collected in anticoagulant for virus isolation, polymerase chain reaction (PCR) and haematology. From the necropsy examination of two to three animals, lymph nodes, especially the mesenteric and bronchial nodes, lungs, spleen and intestinal mucosae should also be collected aseptically, chilled on ice and transported under refrigeration. Fragments of organs collected for histopathology are placed in 10% formalin. At the end of the outbreak, blood can be collected for serological diagnosis. Post-mortem examination of carcasses can be valuable, particularly in wildlife and in situations where samples cannot be kept in suitable conditions during transport to the laboratory, with a view to collection of specimens for detection of multi-nucleated giant cells by histopathology. Infection can be confirmed by identification of the agent with specific tests. Detection of a rise in titre of antibody could also be used, with paired samples collected 14-21 days apart.

Detection of virus antigens by the agar gel immunodiffusion test (AGIDT) is a relatively simple, fast and cheap process. It is extremely useful as an initial test, but it does not discriminate between PPR and rinderpest viruses and further tests are needed to do this. Histopathology combined with immunohistochemical staining (e.g. immunoperoxidase) is a useful procedure because it is performed on formalin-fixed material and can discriminate between PPR and rinderpest when performed with specific monoclonal antibodies. Virus antigens can also be detected by immunocapture ELISA.  

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Antigen-capture ELISA is sensitive and specific, using monoclonal antibodies to give a result with PPR virus and enabling differentiation from rinderpest in small ruminants (Libeau et al., 1994). The availability of the ELISA as a kit has undoubtedly assisted countries in the detection of PPR epidemics. PCR may be of advantage in testing tissues where virus cannot be detected by other means, including specimens for histopathology. However, the time taken to extract RNA, and undertake the RT-PCR is usually longer than that needed for CIEP, and higher technical standards are required to avoid false-positive reactions.  

Antigen-capture ELISA is sensitive and specific, using monoclonal antibodies to give a result with PPR virus and enabling differentiation from rinderpest in small ruminants (Libeau et al., 1994). The availability of the ELISA as a kit has undoubtedly assisted countries in the detection of PPR epidemics. PCR may be of advantage in testing tissues where virus cannot be detected by other means, including specimens for histopathology. However, the time taken to extract RNA, and undertake the RT-PCR is usually longer than that needed for CIEP, and higher technical standards are required to avoid false-positive reactions. Despite these issues it is now commonly used alongside ELISA.

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Antibodies are strongly induced by infection, and become detectable from the diarrheic stage onwards. The prescribed test for international trade (that which is accepted as a basis for the veterinary certification of animals as having evidence of presence or absence of antibodies) is virus neutralisation (VNT; OIE, 2000). Since there is cross-neutralisation between antibodies to PPR and RPV, a positive VNT result to PPR virus needs to be compared to the titre obtained with RPV. The OIE considers that a serum is considered to be positive for PPR when the neutralisation titre is at least two-fold higher for PPR than for rinderpest. Virus neutralisation tests involve use of live virus and cell cultures, and therefore require well-equipped laboratories and biosecurity to prevent escape of virus. VNT is therefore mainly restricted to laboratories with sufficient expertise and through-put of samples to justify the investment involved. The tests are sensitive and specific, and enable differentiation of antibodies to rinderpest virus, should these occur as a result of use of RP vaccine in small ruminants or exposure to the type 1 lineage of RPV. Haemagglutination inhibition tests for antibody have also been described with good correlation with VNT (Raj et al., 2000). After countries have been declared free of rinderpest infection, it may be sufficient to use more simple antibody detection methods that do not require differentiation of RPV infection of small ruminants.

Antibodies are strongly induced by infection, and become detectable from the diarrheic stage onwards. The prescribed test for international trade (that which is accepted as a basis for the veterinary certification of animals as having evidence of presence or absence of antibodies) is virus neutralisation (VNT; OIE, 2000). Since there is cross-neutralisation between antibodies to PPR and RPV, a positive VNT result to PPR virus needs to be compared to the titre obtained with RPV. The OIE considers that a serum is considered to be positive for PPR when the neutralisation titre is at least two-fold higher for PPR than for rinderpest. Virus neutralisation tests involve use of live virus and cell cultures, and therefore require well-equipped laboratories and biosecurity to prevent escape of virus. VNT is therefore mainly restricted to laboratories with sufficient expertise and through-put of samples to justify the investment involved. The tests are sensitive and specific, and enable differentiation of antibodies to rinderpest virus, should these occur as a result of use of RP vaccine in small ruminants or exposure to the type 1 lineage of RPV. Haemagglutination inhibition tests for antibody have also been described with good correlation with VNT (Raj et al., 2000). After countries have been declared free of rinderpest infection, it may be sufficient to use more simple antibody detection methods that do not require differentiation of RPV infection of small ruminants.