Partial characterisation of five cloned viruses differing in pathogenicity, obtained from a single isolate of pigeon paramyxovirus type 1 (PPMV-1) following passage in fowls' eggs.

Viruses with intracerebral pathogenicity indices (ICPIs) of 0.025, 0.55, 1.013 and 1.3. were cloned from a PPMV-1 isolate with an ICPI of 0.32 by passage in embryonated fowls' eggs. Deduced amino acid sequences of the haemagglutinin-neuraminidase (HN) and precursor fusion proteins (F0) showed them to have only a single amino acid difference: those with an ICPI value <0.7 had proline at amino acid position 453 of the F0 protein, and those with an ICPI value >0.7 contained a serine. The virus with an ICPI of 0.025 was further passaged, and the ICPI of non-cloned virus increased to 0.76/0.79, which was then reduced to 0.49 on cloning. The proline at residue 453 was retained, but there were two nucleotide changes in the virus of ICPI 0.49, T --> C at position 1769 in the untranslated region of the fusion gene and G --> A at position 437 of the HN gene, resulting in the amino acid change G --> R at position 116 in the HN protein.