Comparison of immunocapture and RT-PCR techniques for the detection of peste-des-petits-ruminants virus (PPRV) in eye and nose swabs from infected animals

Full text: Peste des Petits Ruminants (PPR) is a highly contagious disease of domestic and wild small ruminants. It constitutes a major constraint on production in areas where it is endemic. Classically, it is characterised by fever, nasal and ocular discharges, diarrhoea, respiratory distress, mucosal erosive lesions and death in 40-80% of acute cases. All these clinical signs, apart from the respiratory symptoms, are very similar to those of rinderpest (RP). The causal agents of both diseases are viruses which belong to the Morbillivirus genus. Described for the first time in 1942 in Cote d'Ivoire, PPR was considered for a long time as a disease of West African countries. The current knowledge on its epidemiology shows that this is no longer true, nor it is a solely African disease since it is widespread in countries lying between the Sahara and the Equator, in the Middle East and in South-West Asia. These data indicate that PPR existed undetected in most of the known endemic areas for a long time. It was overlooked because of the similarity of clinical signs to rinderpest as indicated above and also to pasteurellosis for the bronchopneumonia. The current knowledge of the disease has grown up quickly once specific diagnostic tests became available in the 1990's: serological diagnosis in the competitive format or for antigen detection by immunocapture cDNA probe and the amplification (RT-PCR) technique for the nucleic acid detection. While the immunocapture (ICE) can detect virus up to 100.6 TCID50 of virus in 50μl of sample, the limit of detection of the RT-PCR is estimated to 0.001 TCD50/ml. During a study to analyse the pathogenicity of some PPRV isolates, we have compared the efficiency of the ICE test, antibody-based antigen detection, and RT-PCR, with the RT-PCR, nucleic acid-based detection technique, to detect the shedding of the virus by the infected animals. For the study, Sahelian goats were inoculated IM with PPRV Guinea (isolate from Guinea Conakry) or PPRV C.I. M7 (isolate from Cote d'Ivoire). For the PPRV Guinea strain, the virus was detected by ICE in the nasal and lachrymal swabs from day 1 to 6 after infection. However, the RT-PCR, it was possible to demonstrate the excretion of the virus in the swab until day 8 after infection. With the PPRV CI M7, no virus was detected by ICE in swab after 2 days. But the RT-PCR, virus excretion could be demonstrated up to day 4 post-inoculation. In conclusion, our study has demonstrated that goats can excrete the PPRV very soon after infection by intrasmuscular route. Apparently the amount of the excreted virus is depending to the strain and the time after infection. The RT-PCR can detect the virus excretion in a longer time than can do the immunocapture technique. (author)