Details of the two NDV isolates investigated in this study.

a<p>Mean death time in embryonating eggs (hours) (<60: velogen; 60–90: mesogen; >90: lentogen).</p>b<p>Intracerebral pathogenicity index in day-old chicks (1.5–2.0: velogen; 1.0–1.5: mesogen; <0.5: lentogen).</p>