Studies on Rinderpest Disease in the Sudan

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Mohamed Haroun Ismail Ahmed, Ahmed
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Pathogenesis and immunogenicity of two virulent rinderpest virus (RPV) field isolates and the Old Kabete attenuated RPV vaccine strain (RBOK) were comparatively investigated in two groups of RP-susceptible calves of two cattle breeds. While classical picture of RPV infection was reproduced in susceptible Angus breed subgroup using the virulent RPV-Saudi 1/81 strain, absence of one or more of the RPV cardinal signs was observed in the susceptible Zebu breed calves infected with the virulent RPV reedbuck (RPV -RB) strain. Successful recovery of the virulent RPV -Saudi 1/81 strain from peripheral blood mononuclear cells (PBMCs) from infected control Angus subgroup was attained in B95a lymphoid and modified monocytes human (MoMo) cell lines from day two post-infection till death on day eight. Classical cytopathic effect (CPE) of RPV was reproduced. No virus recovery was attained from PBMCs of the infected Zebu breed subgroup throughout the experiment or from their autopsies six days post infection. Indirect immunofluorescence (IIF) using marinablue stain anti-P monoclonal antibodies (MAbs) showed that RPV -P antigen was expressed on day four in the case of RPV-Saudi 1/81 infected B95a and MoMo cell lines. Polymerase chain reaction (PCR) amplification technology was successfully used to retrieve RPV genomes from PBMCs of RPV- Saudi 1/81 - infected control Angus subgroup on day two of infection till death on day eight and from their ocular and nasal swabs on days 5, 7 and 9 post-infection. RPV genomes were retrieved from 5 out of 9 of the lymphoid tissues of RPV-RB-infected control Zebu calf No. 2476 using RPV -specific primers. Seven out of nine of the same tissues had virus genomes when inner RPV -specific primers (nested PCR) were used. Viral genomes were retrieved from PBMCs of the subject vaccinated Angus subgroup from day two throughout to day nine of vaccination. Ocular and nasal swabs of these animals contained viral genomes on day 9, 12, and 14 of vaccination. Post challenge viral genomes were retrieved from ocular and nasal swabs of these calves on days 5, 7, 9 and 14 of challenge. Viral genomes were also retrieved from mediastinal lymph nodes the vaccinated Zebu calf No. 3390 six days post challenge. Competitive enzyme-linked immunosorbent assay (c-ELISA) demonstrated that the two vaccinated Angus breed calves positively responded to vaccination with the RBOK vaccine strain compared to 6/9 of the vaccinated Zebu calves. The main pattern of the humoral immune response (HIR) followed the previously described pattern for RPV. The first mean positive percentage inhibition (PI) (51.5) was attained two weeks post vaccination in both vaccinated Zebu and Angus subgroups. Mean peak PI of 61.6 and 80.5 reached three and eight weeks post vaccination in Zebu and Angus subgroups, respectively. Mean peak percentage inhibition of 66.8 and 82.0 were scored on days 5 and 12 post challenge, respectively. None of the non-vaccinated control subgroups positively responded to challenge and the highest mean PI was below 30. High populations of lymphocytes were recovered from PBMCs of the Angus breed calves on testing their cell-mediated immune (CMI) response to RPVs. Purity and viability percentages of 97 and 95, respectively were recorded,. Stimulation indices (SIs) as high as 3.9 and 13.2 was shown by PBMCs from the vaccinated calves No. TQ94 and TQ95 on days 5 and 35 of vaccination, respectively. Stimulation index (SI) of 17.55 was shown by PBMCs from calf No. TQ94 two days post challenge while those from calf TQ95 were refractory. None of the non-vaccinated control calves (TQ96 and TQ97) positively responded to the challenge virus and the highest mean SI was 1.41 seven days post challenge. None of the vaccinated subgroups or the three vaccinated non-responder (VNR) Zebu calves succumbed to the challenge with the virulent RPV isolates. The VNR Zebu calves showed antibodies against peste des petits ruminant's virus (PPRV) in their sera. None of the c-ELISA tested field serum samples from cattle, camels, sheep, and goats showed positive RPV- Abs. 11, 14, 51.9 and 56.2% of these sera showed positive PPRV-Abs, respectively. A RPV field isolate (RPV-Sudan /98) was confirmed to be the cause of a suspected RPV outbreak in Torit, Southern Sudan in April 1998 using conventional and nested PCR techniques. Sequencing analysis of its genome related the virus to the African lineage type
Studies on Rinderpest Disease in the Sudan