Going more viral — a postscript to my primer on virology

Simon Morgan is a GP, medical educator and (newly frustrated) travel writer from Newcastle, Australia. He is on Twitter: @drsimonmorgan

A few weeks ago, I wrote a brief primer on virology.° In it, we learnt that viruses are small (in the order of 100 nanometres in diameter), numerous (apparently 100 million times more populous than stars in the universe) and inventively named (like the benevolent-sounding Wild onion symptomless virus). By way of follow up, I can reveal that Fusarium oxysporum Skippy virus does not infect kangaroos and most disappointingly, Arabidopsis thaliana Evelknievel virus, a pathogen of plants, wasn’t so-named because it was observed jumping 25 bacteria lined up end-to-end on a teeny-weeny mitocycle.

The viral replication cycle has six basic stages, but overall reads a bit like a scene from Wedding Crashers.

Let’s start with sex. Sorry, replication. The viral replication cycle has six basic stages, but overall reads a bit like a scene from Wedding Crashers. After binding to specific receptors on the host cell wall, the molecular equivalent to sweet talking the bouncer on the venue door, the uninvited virus then penetrates the cell and maliciously crashes the party. Once inside, it ‘uncoats’ by shedding its outer capsid (picture undressing to its jocks). And then its #trashthejoint. It metaphorically smashes glasses, pukes on the bride’s mother and upends the cake before hijacking the host cell’s molecular machinery to replicate its own genome. Now an unstoppable gang, the newly created viruses collectively flip the bird to the devastated wedding guests, and spill out onto the intercellular street, in search of another cell to infect. Nasty stuff.

Of the nearly 7000 unique species of viruses thus far described, just over 200 are known to cause disease in humans.1 The list I read was alphabetical, from adeno to Zika, but as a GP it would make a lot more sense if arranged into groups of epidemiologically clustered pathogens. There is even an Aussie mob, including Ross River, Barmah Forest, and Murray Valley encephalitis viruses. Three domestic destinations I’ve never been inclined to visit, their respective tourist industries forever marred by having a virus named after them. On that note, a letter published in the journal Science called ‘Naming Diseases; First do no harm’ highlighted the negative impacts and stigmatisation that may stem from inappropriately naming diseases e.g. Middle Eastern Respiratory Syndrome, and cautioned against this practice.2

I could envisage another group of the so-called ‘numbered diseases’. Back in 1905, a Frenchman called Cheinisse coined the term ‘fifth rash disease’ for the relatively newly described childhood illness characterised by a ‘slapped cheek’ appearance, known as erythema infectiosum.3 But why ‘fifth disease’ (la cinqueme maladie)? Because there were already four distinct exanthematous diseases of childhood doing the rounds at the time – in first place, that bad hombre rubeola, or measles; second, scarlet fever (yes, I know it’s not a virus); third, rubella; and missing out on a podium spot, in fourth position, epidemic pseudoscarlatina, or Filatow-Dukes’ disease. In 1910, roseola infantum, also known as exanthmema subitum, became the ‘sixth disease’ to complete the half dozen.

Technically now fifth disease is fourth disease and sixth disease is fifth disease.

In an extraordinary postscript to this story, in 1991 an epidemiological study was published looking at a group of English schoolchildren from the last decade of the 1800s from whom the original fourth disease diagnosis was based.4 The authors concluded that Filatow-Dukes’ disease never actually existed and that the cases were misdiagnosed rubella and scarlet fever. So technically now fifth disease is fourth disease and sixth disease is fifth disease. It’s a bit like disqualifying a doping cyclist from the Tour de France years after the event and shuffling everyone up the rankings.

To be honest, I’m kind of glad they gave up this particular classification system, as it couldn’t have kept pace with modern day virology. ‘You have a virus – we call it one hundred and seventeenth disease’ doesn’t quite work.



1. Woolhouse M et al. Human viruses: discovery and emergence. Philos Trans R Soc Lond Biol Sci 2012. 367; 1604: 2864-71.
2. Fukada K, Wang R, Vallat B. Naming diseases: First do no harm. Science 2015; 348(6235):643.
3. Cheinisse L. Une cinquieme maladie eruptive: le megalerytheme epidemique. Semaine Medicale 1905; 25: 205-7.
4. Morens DM, Katz AR. The “Fourth Disease” of Childhood: Reevaluation of a Nonexistent Disease. Am J Epidemiol 1991.134; 6: 628-40.



Featured photo by Daniel Cheung on Unsplash with additional image by Annalise Batista from Pixabay.

Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Inline Feedbacks
View all comments
Previous Story

Interpreting antibody tests with care

Next Story

General practice post COVID: time to put equity at the heart?

Latest from Coronavirus

Would love your thoughts, please comment.x