A more toxic form of Strep A is circulating in Australia, but is it causing disease?

A new Group A Streptococcus variant imported from the UK is now circulating in Australia, with researchers racing to identify whether it’s the cause of related diseases being reported across the country.

The variant, named M1uk, has been associated with surges in scarlet fever in the United Kingdom. It’s now the dominant form of the bacteria there and in the Netherlands.

Streptococcus is an often harmless organism that exists on the skin, but in some cases it can infect parts of the body.

Group A Streptococcus (Strep A) diseases include the simple sore throat, a more severe throat infection called pharyngitis and rash-forming illness like scarlet fever and impetigo.

But there are particularly dangerous Strep A infections.

Invasive group A Streptococcus – or iGAS – diseases occur when the bacteria infects crucial parts of the body leading to severe illness. These include sepsis, meningitis, toxic shock syndrome and flesh-eating disease.

Five-fold toxin enhancement, but is it connected to more disease?

When it began spreading in the UK, British researchers found the expression of a particular toxin-coding gene within M1uk was five times higher than the ancestral Streptococcus species.

Previous studies have shown this toxin can indirectly drive human immune responses in serious infections.

The researchers behind the Australian study from the Doherty Institute and the universities of Melbourne and Queensland now want to learn whether that increased toxicity is causing iGAS cases down under.

“Clinically, we’ve seen a change in cases in Australia, so it’s kind of connecting the dots: if this this clone is here, then maybe it’s one of the reasons why we’re seeing an increase in invasive group A Strep in Australia,” says lead researcher Dr Mark Davies from Melbourne University.

The challenge for bacteriologists like Davies and his colleagues is to establish a concrete connection between the new strain and what appears to be an increase in cases.

iGAS diseases are nationally notifiable, so newly detected cases must be reported to state and territory health authorities and added to the federal government’s surveillance database. Nearly 500 iGAS cases were reported in the last quarter of 2022. More than 300 have already been reported this year.

But because iGAS became nationally notifiable in 2021, only 24 months of national surveillance data is currently available to assess. That makes it difficult to reliably determine trends when a new strain of bacteria is found in circulation.

Davies says surveillance for the M1uk strain will benefit from a new national genomic surveillance program that improves the way notifiable pathogens are reported to health authorities.

While case numbers are reported to health authorities, genomic surveillance will better connect that data to the specific pathogen causing the disease.

This involves notifiable cases providing specimens – often in the form of a blood sample – to clinicians who send the sample away for laboratory testing.

Davies is optimistic that introducing a widespread genomic surveillance system will help lab scientists provide near real-time data to health authorities to improve public health responses to disease in the community.

“A national genomic framework will link in with what we’re seeing with those clinical cases, so when we’re seeing changes, is that due to a change in the bug or other factors?” says Davies.

“We’re going to be in a much better position to guide some public health response, we can detect these books much more quickly, and whether they are the new variants.”

An mRNA-based vaccine addressing Strep A bacteria is currently in development.

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