ASSESSMENT OF NOVEL N-GENE TARGET FOR DETECTION OF PESTE DES PETITS RUMINANTS (PPR) VIRUS BY RT-PCR AND CHARACTERIZATION BY RFLP PROFILE
Abstract
Peste des Petits Ruminants (PPR) is an economically important viral disease of sheep and goats, characterized by high fever, ocular and nasal discharge, pneumonia, necrosis and ulceration of the mucous membrane and inflammation of gastrointestinal tract leading to severe diarrhea. The disease is caused by a Morbillivirus of the family Paramyxoviridae. The disease is highly contagious causing varying degree of morbidity and mortality in susceptible animals. In India, severity of the disease is more pronounced in goats than in sheep and with a combined susceptible population of about 200 million, it is one of the major threats to the small ruminant population of the country. The present study was aimed to study the incidence of Peste des petits ruminants virus (PPRV) in goats of selected areas of Gujarat by sandwich ELISA and to derive estimates of overall, locationwise, agewise and sexwise incidence and samplewise positivity rates. In addition, the study also involved standardization and application of novel Nucleocapsid (N) gene based RT-PCR, for diagnosis of PPR. Further, an attempt was also made to access possible genetic variation among the field and vaccine PPRVs by RFLP profile. A total of 46 clinical samples from 31 goats suspected of PPRV from selected areas of Gujarat were tested by sandwich-ELISA, of which 23 animals were found positive yielding an overall incidence rate of 74.19 percent. Out of 18 animals suspected of PPR at Clinical Service Complex, Veterinary College. Anand, 15 (83.33%) were found positive; whereas four (80%) out of five samples from Koth, two (66.67%)) out of three samples from Vasna and two (40%) out of five samples from Harsoli yielded positive results. Out of the 31 animals, 13, 11, 6 and one animals belonged to age groups of 0-12, 12-24, 24-48 and >48 months, respectively, showing the respective incidence of PPRV as 84.61, 63.63, 66.67 and 100 per cent. Incidence rate of PPR by sandwich-ELISA was 80%) and 71.43%) in males and females, respectively. The PPRV antigen could be detected slightly more in blood samples (73.33%) than in nasal swabs (66.67%o), in case where both the sample types were taken from the same animals. All the 46 clinical samples, a reference vaccine virus (Sungri isolate) and a blood sample from apparently healthy goat were processed for RNA extraction using TRI Reagent . RNA samples showing acceptable purity and concentration were reverse transcribed with random hexamers to generate cDNA templates, which were subjected to PCR amplification using in silico designed N-gene specific primer pair N1-N2. Reference vaccine virus as well as fifteen (32.61%) of the 46 clinical samples, including fourteen blood samples and one nasal swab, produced the desired amplion of approximately 463 bp with primer pair N1-N2. The amplicons from all the positive samples and the vaccine virus migrated similarly in the gel. Thirty one (67.39%)) samples including 12 blood samples, 17 nasal swabs and two tissue samples as well as the blood sample taken from apparently healthy goat failed to produce the targeted amplification with the primer pair N1-N2. Out of 46 clinical samples tested for PPRV, 31 and 15 samples were positive by sandwich-ELlSA and RT-PCR, respectively. "None of the samples negative in sandwich- ELISA yielded positive amplification in RT-PCR. Relative to sandwich-ELlSA, sensitivity and specificity of the RT-PCR was 48.39 and 100.00 per cent, respectively. Overall agreement between the two tests was 65.22 per cent. RT-PCR products (463 bp) amplified with primer pair N1-N2, were further digested with two restriction enzymes viz. Pst-I and Alu-I for RFLP analysis. RT-PCR products of the representative samples from each of the three locations and the reference vaccine virus produced similar RFLP patterns with each of the two REs, indicating absence of genetic variation at the corresponding restriction sites of these two REs. Digestion of RT-PCR products with Alu-l yielded a fragment of 395 bp, whereas the other fragment was not visible. Similarly, digestion with Pst-I yielded a single fragment of405bp.
Description
Keywords
VETERINARY MICROBIOLOGY, ASSESSMENT