Molecular Evolution of the F Glycoprotein of Human Parainfluenza Virus Type 1

Human parainfluenza virus type 1 (hPIV1) is a major cause of upper and lower respiratory tract infections among children. Immunity is mediated at least in part by antibody to the fusion (F) surface glycoprotein. Thus, genetic variation in the F gene could influence host range, virulence, and immunity. To examine the genetic diversity among hPIV1 isolates, the F genes of hPIV1 isolates from a single geographic location were sequenced and compared with the F gene of a strain isolated in 1957. Genetic variation was 2.2%-3.4%, averaging 0.8 amino acid changes per year. Changes were progressive over time, and virus evolution was dominated by a single lineage. Three of 7 isolates tested did not induce syncytium formation in tissue culture. This phenotype could not be ascribed to a single unique mutation in the F gene, but these 3 isolates had mutations in the transmembrane region of the HN gene. It is unlikely that the limited genetic evolution of the F gene will be an obstacle to vaccine development.