Scientists discovered a new strain of group A streptococcus bacteria

A team of scientists led by Imperial College London have discovered a new strain of group A streptococcus bacteria.


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Group A streptococcus is a bacterium often found in the throat and on the skin. It is known to cause known to cause scarlet fever, throat infections and – in very rare cases – invasive disease, where the bacterium enters the bloodstream or tissue and can trigger sepsis and toxic shock.

In a new study, scientists at the Imperial College London have discovered a new strain of group A streptococcus bacteria called M1UK tht causes Strep A infections.

The new strain delivers one kind of streptococcal toxin more than existing strains – making it conceivably potentially to cause common throat infactions scarlet fever, which could represent an ascent in invasive infection.

The first outbreak of the infection was found in England and Wales since 2010 to become the dominant cause of Strep A infections. The team add the new strain can be easily treated with antibiotics. The study suggests the new strain has increased in numbers among cases of scarlet fever, throat infections and much rarer invasive infections since 2014. Scientists noticed 1.5x increase in the number of laboratory-confirmed invasive group A streptococcus infections in 2016.

Professor Shiranee Sriskandan, senior author from the Department of Infectious Disease at Imperial said: “We’ve seen an unprecedented rise in the number of cases of scarlet fever since 2014 but it was only in 2016 there was a rise in the number of serious, invasive cases due to Strep A – which are thankfully very rare- coinciding with the seasonal rise in scarlet fever. Our research, done in collaboration with Public Health England, aimed to determine if there was a link between the increase in scarlet fever and the increase in invasive infections. In undertaking this research, we identified the new strain type, linked to increases in both.”

“Scarlet fever is a very visible signal of how much Strep A is circulating in the wider community, and causing sore throats. Strains of Strep A that cause these commoner throat infections and scarlet fever are the same strains that cause rarer invasive diseases – and therefore a rise in these commoner throat infections including scarlet fever could lead to increases in all forms of Strep A infection.”

Scientists identified infections between the spring times of 2014-2016 to identify the main genetic subgroups causing scarlet fever or common throat infections.

The London data revealed that although most cases in 2014 were caused by strains emm3 and emm4, infections of emm1 strain increased year-on-year – responsible for 5% of cases in 2014, 19% in 2015 and 33% per cent in 2016.

Scientists identified for the presence of the new strain in samples from 552 cases of emm1 invasive Strep A in England and Wales between the spring time periods of 2013-2016. The results revealed 77% of cases of invasive disease caused by emm1 Strep A in England and Wales in spring 2016 were caused by the newly identified M1UK strain.

When the analysis expanded to include all emm1 strains (1240 strains) that had been sequenced over a 10 year period from across the UK mainly from invasive cases of the disease, this reached 84 per cent of emm1 samples by 2016.

Dr Elita Jauneikaite, first author of the study from Imperial College London explained: “There is still uncertainty around the cause of the rise in scarlet fever – and whether it is a result of practice change, population or environmental factors. Research investigating the most appropriate way of reducing the burden of Strep A infections is currently underway – including work into developing a vaccine. We may also need to consider whether guidelines for diagnosing and treating throat infections may need to take evolution of new strains and complications like scarlet fever and invasive infections into account.”

Dr Nicola Lynskey, co-first author, added: “The emergence of this new strain suggests we may need increased surveillance of the type of strains causing scarlet fever, throat infections and sepsis – both at a UK and global level.”

Dr Theresa Lamagni, Public Health England, said: “Public Health England will continue to work with partners to investigate the resurgence of scarlet fever and better understand the spread of this infection in different settings and patient groups. Through monitoring changes we can assess the impact on any new strains on patients and ensure rapid response to emerging threats.”

The study is published in the Lancet Infectious Diseases.