Viral proliferation patterns of a velogenic (VLT), a mesogenic (Komarov), and a lentogenic (F) strain of Newcastle disease virus.

A highly pathogenic and two avirulent vaccine strains of Newcastle disease virus were investigated quantitatively for their proliferation in various tissues of experimentally infected SPF chickens. Virulent strain VLT multiplied extensively in all the tested tissues whereas a mesogenic strain (K) was not detected in the brain during the period of observations. A lentogenic strain (F) was only detected in moderate quantities in trachea. The development of antibodies seemed to correlate with the disappearance of the two avirulent strains from the tissues.