Genetic variation and evolution of human parainfluenza virus type 1 hemagglutinin neuraminidase: analysis of 12 clinical isolates.

The extent of genetic variation and evolution in a population of human parainfluenza virus type 1 was investigated. The hemagglutinin neuraminidase genes of 13 isolates collected over a 26-year period were sequenced and compared. All isolates except the 1957 type strain were from a single geographic location and demonstrated significant consistent genetic change from the type strain (47/7 nucleotide/amino acid] substitutions). Antigenic subgroup A isolates demonstrated minor intragroup differences (9/1 substitutions). However, 18/7 unique substitutions separated subgroup A from B regardless of geographic location or year of isolation. Multiple strains of both subgroups appeared and reappeared over decades with only minor variation. There may be significant genetic differences between clinical isolates based on geographic location, and progressive mutational change may occur. Previously defined antigenic and now genetic subgroups were stable and at least regional in distribution over the period studied. The biologic implications and extent of this variation need further evaluation.