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.
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.
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.