The chronicles of coronaviruses: the electron microscope, the doughnut, and the spike

Abstract

The advancement of medicine owes in large measure to a German engineer Ernst Ruska, whose invention of transmission electron microscope in 1931 won him the 1986 Nobel Prize in Physics, when it comes to infectious diseases. Encouraged by his physician brother Helmut Ruska to use the prototype instrument for the study of viruses, the course of virology was shifted to a different and unprecedented level. Virus could then be seen, identified and imaged. The University of Maryland happened to acquire an American model of transmission EM, the RCA EMU, using which the first structural study was done for the first known coronavirus (then was simply known as infectious bronchitis virus) in 1948. The virus was described as rounded bodies with filamentous projections. The magnification was not great and the resolution was poor. The study was followed by a series of studies using improved techniques and better EM spanning the next decade. An upgraded version RCA-EMU2A gave better images in 1957 and the virus was described as doughnut-like structure. Using Siemens Elmiskop, D.M. Berry and collaborators made the first high-resolution pictures in 1964. The thick envelope which gave doughnut-like appearance and filamentous projections reported before could be discerned as discrete pear-shaped projections called the spikes. These spikes form a corona-like halo around the virus, which were also seen in novel human viruses (B814 and 229E) that caused common colds. The discoverer of B814, David Tyrrell and his aid June Almeida, a magnificent electron microscopist, established that IBV, B814 and 229E were of the same kind of virus in 1967, which prompted to create the name coronavirus in 1968. This article further highlights the detail structural organisation of coronaviruses emanating from these pioneering research.