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A team of international researchers including Doherty Institute’s Dr Mark Davies say supercharged “clones” of the bacteria Streptococcus pyogenes are to blame for the resurgence of scarlet fever, which has caused high death rates for centuries.

After being almost eradicated in the 1940s, the re-emergence of the pandemic has seen a more than five-fold increase in disease since 2011 and more than 600,000 cases around the world.

Led by the University of Queensland, the team found a variety of Streptococcus pyogenes bacteria that had acquired “superantigen” toxins, forming new clones. The research was published today in Nature Communications.

“Streptococcus pyogenes bacteria are usually spread by people coughing or sneezing, with symptoms including a sore throat, fever, headaches, swollen lymph nodes, and a characteristic scarlet-coloured, red rash,” Dr Stephan Brouwer from the University of Queensland said.

“Scarlet fever commonly affects children, typically aged between two and 10 years. After 2011, the global reach of the pandemic became evident with reports of a second outbreak in the UK, beginning in 2014, and we’ve now discovered outbreak isolates here in Australia.”

University of Melbourne Dr Mark Davies, a laboratory head at the Doherty Institute said by combining genomic and laboratory-based experimental models, the team was able to unravel how bacterial toxins can change the ability of Streptococcus pyogenes to cause infections like scarlet fever.

“This work provides new insight into how viruses that affect bacteria can change the ability of Streptococcus pyogenes strains to cause infections like scarlet fever,” he said.

“Now, my team is developing molecular surveillance tools to track the spread of disease causing Streptococcus pyogenes around the world.”

Professor Mark Walker from the University of Queensland, explained that it was supercharged bacterial clones that have been causing modern scarlet fever outbreaks.

“This year COVID-19 social distancing has kept scarlet fever outbreaks in check for now,” Professor Walker said.

“But when social distancing eventually is relaxed, scarlet fever is likely to come back. We need to continue this research to improve diagnosis and to better manage these epidemics.

“Just like COVID-19, ultimately a vaccine will be critical for eradicating scarlet fever – one of history’s most pervasive and deadly childhood diseases.”

This research was a collaboration between UQ, Telethon Kids Institute, University of Wollongong, Western University Ontario, Doherty Institute, University of Cambridge, University of California San Diego, The University of Hong Kong and the Chinese Centre for Disease Control and Prevention.

This research has been published in Nature Communications.