Evaluation of a thermostable Newcastle disease virus D58 strain by in ovo vaccination and challenge study.

The persistent incidence of Newcastle disease (ND) in vaccinated flocks highlights the limitations of conventional vaccination and necessitates improved strategies like in ovo vaccination. This study evaluated the protective efficacy of a live, thermostable Newcastle disease virus (NDV) strain D58 (genotype II) in two groups of chicks (each n = 12), either delivered in ovo on embryonic day 18, or by intraocular vaccination in 7-day-old chicks. Two more groups (each n = 12) vaccinated through the in ovo or intraocular routes with commercial F strain were included for comparison. An unvaccinated group (n = 12) was used as a control. All groups were challenged with the virulent NDV D162 strain (genotype XIII) at 35 days post-hatch to assess cross-protective efficacy. Serological responses, clinical protection, viral shedding, cell-mediated immunity, and histopathological changes were assessed. The in ovo D58 group exhibited early seroconversion with significantly higher antibody titers by day 7 post-hatch. This group demonstrated 100% clinical protection, the lowest viral shedding, and enhanced cell-mediated immunity, evidenced by superior lymphocyte proliferation and cytokine gene expression. Histopathology revealed minimal lesions in the in ovo D58 group, contrasting with marked pathology in controls. In ovo D58 administration provides rapid protection and cross-protective efficacy against heterologous challenge.