Electron tomography of negatively stained complex viruses: application in their diagnosis

BACKGROUND Electron tomographic analysis can be combined with the simple and rapid negative staining technique used in electron microscopy based virus diagnosis. METHODS Standard negative staining of representative examples of parapoxviruses and paramyxoviruses was combined with electron tomographic analysis. RESULTS Digital sectioning of reconstructions of these viruses at a selected height demonstrated the viral ultrastructure in detail, including the characteristic diagnostic features like the surface threads on C-particles of a parapoxvirus and individual glycoproteins and the internal nucleoprotein strand of Newcastle disease virus. For both viruses, deformation and flattening were observed. CONCLUSION The combination of negative staining of complex viruses with electron tomographic analysis, allows visualizing and measuring artifacts typical for negative staining. This approach allows sharp visualisation of structures in a subnanometer-thick plane, avoiding blurring due to superposition which is inherent to TEM. In selected examples, such analyses can improve diagnosis of viral agents.