Structural variation of La Crosse virions under different chemical and physical conditions.

La Crosse (LAC) virions exposed to different pHs (7.3, 6.2, and 5.4) and temperatures (37 degrees, 20 degrees, and 4 degrees) were preserved in thin layers of vitreous ice and observed by electron cryomicroscopy. Our results indicate that, at lower pH, virus particles interact with each other to form aggregates. In some cases, particles could be interpreted to have fused together. At neutral pH and higher temperatures morphological changes consistent with deformation in some particles were observed. We suggest that low pH conditions are sufficient for membrane fusion events to occur with LAC virions.