Newcastle disease virus in Taiwan: II, Relationship between polykaryocytosis and virus virulence

Area of Science:

• Veterinary Virology
• Avian Pathology
• Molecular Biology

Background:

• Newcastle disease virus (NDV) is a significant pathogen affecting poultry worldwide.
• Understanding the relationship between NDV virulence and its biological characteristics is crucial for disease control.
• Cytopathic effects, including polykaryocytosis, are key indicators of viral activity and pathogenicity.

Purpose of the Study:

• To investigate the correlation between the virulence of different NDV strains and their ability to induce specific types of polykaryocytosis.
• To evaluate various parameters of NDV pathogenicity, including cell culture effects, embryo infectivity, and pathogenicity indices in chicks.

Main Methods:

• Assessed cytopathic effects in chick embryo kidney (CEK) and BHK-21 cells.
• Determined egg-infectious units in chick embryos (CE).
• Measured virulence using mean death time, intracerebral pathogenicity index (ICPI), and intravenous pathogenicity index (IVPI).
• Quantified fusion from within (FFWI) and fusion from without (FFWO) in monolayer cell cultures.

Main Results:

• A strong correlation was observed between the capacity of NDV strains to induce FFWI at 15 hours post-infection and their virulence in both chick embryos and chicks.
• No significant relationship was found between the ability of NDV strains to induce FFWO and their measured virulence.
• Varied levels of virulence and cytopathic effects were noted across the selected local isolates and known NDV strains.

Conclusions:

• The induction of fusion from within (FFWI) in cell cultures serves as a reliable indicator of Newcastle disease virus virulence.
• Fusion from without (FFWO) is not a suitable marker for predicting NDV pathogenicity.
• Further research into the mechanisms of NDV-induced cell fusion could offer insights into viral pathogenesis and inform vaccine development.