Clinicopathological evaluation of Newcastle disease virus vaccination using gums from Cedrela odorata and Khaya senegalensis as delivery agents in challenged chickens

Abstract

Following previous studies on delivery potential and immune response of chickens given Newcastle disease vaccine with gums, this study was conducted to evaluate the protective ability of vaccines delivered with plant gums against clinicopathological features of Newcastle disease (ND). Processed gums from incised trunks of Cedrela odorata and Khaya senegalensis trees were combined with ND vaccine in ratio 2:2:1 and administered at 21 days to white leghorn cockerels after weaning of maternal antibodies. The birds were grouped into gum-vaccine-oral (GVOR), vaccine-oral (VOR), gum-vaccine-ocular (GVOC), vaccine-ocular (VOC), gum-oral (GOR), gum-ocular (GOC), no-gum-no-vaccine/challenged (NGNV/C), no-gum-no-vaccine/unchallenged (NGNV/U). Vaccination was boosted with the same preparation at day 42 while birds were challenged with live ND virus (KUDU strain) at day 84. Clinical signs (Dullness, Diarrhoea, Paralysis, Torticollis) Post infection (Pi), terminal weakness, gross and histology lesions were scored on a severity scale from absent (0-), mild (1+) to moderate (2+) and severe (3+). Scores were assigned a quantitative score of 0, 10, 20, 30 respectively. Clinical signs scores for the 5 week Pi were subjected to Friedman test to assess the significance of severity among the groups. The test was significant at 1% significance level which implies that the clinical signs ranked highest in the NGNV/C, followed by the Gum alone groups, the vaccine alone groups and the gum-vaccine groups irrespective of route. Moribund birds subsequently euthanized were seen in the GOR and GOC group at 21% each and at 57% in NGNV/C group alone. No signs were seen in the NVNG/U group. Grossly, mild to moderate lesions were seen in all groups except GVOR and NGNV/U. At histology, pulmonary congestion, acute pneumonia, cecal tonsilar haemorrhages, gliosis and neuronophagia were present at different proportions in all groups except the GVOR and NGNV/U. Overall, lesion severity was least in the gum-vaccine groups while the oral groups had less lesion score compared to the ocular. From this study, phytogenic mucoadhesives polymers used hold immense potential as a delivery agent capable of improving protection against clinicopathologic features of Newcastle disease in previously vaccinated birds. Keywords: Vaccines, Chickens, Mucoadhesives, Gums, Newcastle disease, Pathology