Visualising Viruses

Viruses pose a challenge to our imaginations. The structures of some virus particles have been determined experimentally in great detail, but for many important viruses a detailed description of the virus particle is lacking. This can be because they are challenging to describe with a single experimental method, or simply because of a lack of data. In these cases, methods from medical illustration can be applied to produce detailed visualisations of virus particles which integrate information from multiple sources. This approach was used to visualise the highly variable virus particles of influenza A viruses and, in the early months of the COVID-19 pandemic, the virus particles of the then newly characterised and poorly described SARS-CoV-2. How constructing integrative illustrations of virus particles can challenge our thinking about the biology of viruses.

Influenza viruses, as studied in the laboratory, are rather more regular than those that occur in natural infections. Laboratory-adapted strains of influenza virus typically form spherical or bacilliform virions of around 120 nm diameter, but low-passage clinical isolates can form additional, filamentous virus particles that are slightly narrower and can extend for microns in length, reaching tens to hundreds of times the length of the spherical particles.To address this, we built models of intact influenza virus particles using Autodesk 3ds Max .These were constructed at low resolution, as capsules decorated with simple geometric models of the surface proteins haemagglutinin (HA) and neuraminidase (NA).

A detailed model of a bacilliform IAV virus particle showing proteins encoded by both the virus and its host. Host proteins and membrane are in brown, reds and oranges; viral proteins are polymerase trimer (light green) and NP (light blue) in the RNPs; and HA (blue), NA (red), M2 (pink), M1 (dark green), NEP and NS1 (both  purple).

Modelling SARS-CoV-2 particles, which showed that spike proteins were present at a lower density on the surface of SARS-CoV-2 than we had predicted from studies of murine hepatitis virus and SARS-CoV-1, and that the spike proteins could bend both with respect to the membrane and along their stems.

(a) An initial model of a SARS-CoV-2 virion, produced in the early months of the COVID pandemic and partly based on studies of related coronaviruses. S proteins are purple, M proteins blue, E proteins green, N proteins yellow, and genomic RNA red. (b) A revised model incorporating information from experimental studies of SARS-CoV-2.

Visualisations of virus particles can also be used more deliberately as resources for science communication. The level of detail in these structures means that they can be used to explain the relationship between the underlying molecular biology of these viruses and their impact on our lives.