Purpose: Investigate the degree and mechanism of strain-specific variability in human norovirus heat resistance.
Methods: Virus-like particles (VLPs) of two different epidemic genotype GII.4 strains (Sydney, SYV; Houston, HOV) and one GII.2 strain (Snow Mountain, SMV) were used. The VLPs were subjected to different heat treatments (time-temperature combinations) and capsid functionality assessed using receptor and aptamer binding assays. The impact of heat on VLPs was also analyzed using dynamic light scattering (DLS) and transmission electron microscopy (TEM). Ligand docking and molecular dynamics (MD) simulations were done to predict capsid structural differences that mediate thermal resistance.
Results: SMV and SYV displayed much greater heat resistance than HOV. For example, treatment at 70°C for one minute resulted in loss of 47.6±5.3% of binding signal for HOV but had little impact on SYV (2.7±4.5% loss) or SMV (0.9±2.6% loss). At 65°C, 36.3±6.1% of receptor binding for SYV was lost after 25 minutes while HOV lost 35.5±9.2% after only 3 minutes. DLS and TEM data confirmed the ligand binding findings. Ligand docking simulations located aptamer binding in the same capsid region as histo-blood group antigen binding. MD simulations revealed that HOV had lower P-to-P-domain hydrogen bonds and more solvent accessible area compared to SYV and SMV.
Significance: Human norovirus displayed significant strain-to-strain variability in thermal resistance, a phenomenon likely associated with capsid structure. These differences have implications for food and environmental control measures, especially given the high degree of epidemic GII.4 strain capsid sequence variability.