The invasive strep A variant first identified in the UK and thought to be behind a surge in deaths there and throughout Europe has likely contributed to a similar uptick in serious disease and hospitalisations in Australia, researchers say.
While most people who get strep A will not become extremely sick, the bacteria can lead to severe life-threatening infections. A mutant strep A strain, named M1UK, was discovered in the UK in 2019 and has been since been linked with surge in scarlet fever cases, severe infections known as “invasive strep A”, and deaths.
While health authorities in Australia only recently began recording strep A cases nationally, so statistics on cases are difficult to map over time, Victoria and New South Wales are among the states to have issued warnings to be on alert for symptoms. Health authorities in the UK say between September and January, invasive strep A led to the deaths of 30 children. A further 10 children have died since then in the UK.
In a paper published in the journal Nature Communications this month, researchers from the Doherty Institute and the University of Queensland’s Institute for Molecular Bioscience reported the detection of M1UK in Australia for the first time. They also discovered what makes the variant markedly different to the original bacterium, finding it produces significantly higher levels of a toxin than the previous strain.
A co-lead author of the paper, Dr Mark Davies, said until December, invasive strep A was not a nationally notifiable disease. Notifiable diseases are those that must be reported to the Department of Health so that cases and spread can be monitored.
“At the time we began this research there was no systematic surveillance of strep A, so we went to our colleagues and asked them if they had any strep A isolates in their freezer that we could genome sequence to understand whether it is the new clone or not,” Davies said.
Genomic sequencing is the process of determining the entire genetic makeup of an organism, such as bacteria or a virus.
“They were able to send us the data back to 2020,” Davies said. “And it’s taken us a couple of years to compile the complete story.”
What they found is that M1UK makes a lot more of a super-antigen, or toxin, Dr Joshua Osowicki, a paediatric infectious diseases physician at the Royal Children’s hospital in Melbourne, said.
“The really interesting part of their research is that they have answered the question [of] what makes this strain so much fitter,” he said.
“They found that this strain makes five times as much of this key toxin as the previous strain. And that is the biggest explanation for why this strain has crowded out the old one. So this group sequenced this strain, compared it to the previous strain, and from there did as series of experiments to show how that affects the way it behaves.
“It’s a whole other challenge to do what these researchers did and to understand the real-life impact of the changes to the variant and pick them apart to find this one change that is really responsible for everything.”
Osowicki said when it replicated, the M1UK strain was failing to “take the genetic foot off the pedal” at the point where it was supposed to stop producing the toxin.
“The internal quality control system has been circumvented and you end up with five times as much of this toxin,” he said.
Strep A is also behind rheumatic heart disease, a disease of severe social disadvantage found in developing countries and in Indigenous Australian communities. Osowicki said it would take some time to gather enough data to establish if M1UK was leading to an uptick in rheumatic heart disease, especially given it takes repeated and untreated infections for rheumatic heart disease to occur.
Davies said that since his team conducted their analysis of M1UK, other strains of strep A had also begun circulating throughout Australia. Given M1UK is one of several variants circulating, it is likely partly behind the rise in serious strep A infections and deaths.
The findings show why there is an urgency to develop a vaccine as new fitter strains like M1UK emerge, he said. While such a vaccine is likely years away, Davies said funding and collaboration meant “Australia is leading the way with a vaccine against this bug”.
