Refreshment of a virulentic strain of Newcastle disease virus in chicken embryos and testing its pathogenic properties on chickens

The preservation of strain viability and maintenance of their valuable properties are critical prerequisites for all stages of microorganism research, ranging from initial characterization to their application in the production of various biopreparations. This study investigates the revitalization of the virulent Newcastle disease virus (NDV) strain "T-53" in developing chicken embryos (DCE) and evaluates its pathogenic activity in chicks.After nine years of storage, the biological activity of the "T-53" NDV strain declined to 1.74 lg EID50/ml. Following three successive passages in DCE, the biological activity of the strain was restored to a level suitable for long-term storage. The virus-containing suspension produced was subsequently lyophilized with the addition of a protective medium in accordance with the strain's passport specifications. The quality of the lyophilized strain was evaluated using several key parameters, including appearance, absence of foreign impurities, mold, and ampoule cracks, presence of vacuum, solubility, pH value, moisture content, sterility against bacterial, fungal, and mycoplasmal contaminants, biological activity, and pathogenicity.The findings confirmed that the physicochemical and biological properties of the revitalized "T- 53" NDV strain correspond to the specifications outlined in its passport, ensuring its suitability for further use and long-term preservation.