Cosmos Q&A: A forgotten foe returns

Scarlet fever was a feared disease until well into the 20th century. Characterised by a red, sandpapery rash, it typically infected children and caused notable numbers of deaths. After being reduced to isolated cases for decades it re-emerged this century.

Cosmos asked University of Queensland (UQ) Professor Mark Walker, about research into the scarlet-fever causing bacteria Streptococcus pyogenes that’s just been published in Nature Communications. Walker was one of the supervisors of the UQ-led international research team.

A lot of people would be surprised to hear that scarlet fever’s still around. When did health authorities have it mostly “managed”, and when did it re-emerge?

Scarlet fever was a major problem in the 19th and early 20th centuries. This was the time before antibiotics, and unresolved scarlet fever could go on to cause sepsis and invasive infections, with associated significant mortality in children. Scarlet fever then abated when antibiotics became widespread, until it was thought of as a “Dickensian disease”, with only sporadic cases occurring.

Scarlet fever cases then arose again in Hong Kong and China in 2011 and in the UK in 2014. In these health jurisdictions, scarlet fever is notifiable. We made the first report of the detection of a scarlet fever outbreak strain in Australia in 2019.

Where have cases been detected, and in what numbers, since its re-emergence? Have there been fatalities?

The first cases of scarlet fever investigated in Hong Kong were associated with invasive infection, but deaths are rare, due to appropriate antibiotic treatment. Overall, there have been less than 600,000 cases of scarlet fever reported in the UK, Hong Kong and China since 2011. Because scarlet fever is notifiable in these health jurisdictions it’s much easier to track, compared to Australia and other countries.

Your work has uncovered supercharged “clones” of the bacteria Streptococcus pyogenes, which you’ve learned are responsible for scarlet fever’s return. Can you tell us more about these clones – how do they assist the bacteria? Have we any idea as to why they may have emerged, and when?

We have reported a new combination of three toxins that have been found in scarlet-fever causing strains. We have generated evidence, using animal models, that this new toxin combination helps the bacteria colonise the host. We hypothesise that this enhances capacity to colonise and infect the host, along with the action of the three-toxin combination, has triggered these new scarlet fever outbreaks.

We understand that COVID-19 social distancing measures have reduced scarlet fever outbreaks this year. Should we anticipate its return when public health measures change?

Social distancing and other COVID19 measures seem to have reduced scarlet fever cases. It is likely that there will be more scarlet fever cases when social distancing measures are lifted.

You’ve said that ultimately a vaccine will be required to eradicate scarlet fever. Has work commenced on that? What steps are required to get to that stage?

My lab and many others worldwide are trying to develop a vaccine against the bacterium Streptococcus pyogenes, the causative agent of scarlet fever. [Pharmaceutical companies] GSK and Merck have also been trying to develop a vaccine. However, as we have seen for COVID-19, the development of an effective vaccine and taking it through human trials is a difficult and expensive process.