‘Toxigenic’ strain of Strep A is ‘behind the surge in scarlet fever’

New strain of Strep A that is NINE TIMES more aggressive is ‘behind the record-high number of cases of scarlet fever in England’

  • Scientists analysed strains of the bacteria in England and Wales from 2014-to-16
  • Streptococcus pyogenes strain caused cases to spike to 15,000 in 2014
  • Cases rose to over 17,000 cases in 2015 and more than 19,000 in 2016

An aggressive strain of Strep A is thought to be behind an ‘unprecedented’ surge in scarlet fever since 2014, research suggests.

Scientists at Imperial College London analysed strains of the bacteria that circulated in England and Wales from 2014-to-2016.

They identified strains of the bug Streptococcus pyogenes produce up to nine times more of the ‘scarlet fever toxin’.  

These are thought to have caused cases of scarlet fever to spike to more than 15,000 across England in 2014 – the highest level since the 1960s.

Numbers have continued to rise since then, with over 17,000 cases in 2015 and more than 19,000 in 2016, statistics show.

A ‘more toxigenic’ strain of Strep A is thought to be behind the surge in scarlet fever cases since 2014. Scarlet fever causes a tell-tale red rash. Starting on the neck, underarm and groin, it spreads over the body, resulting in small bumps that feel like sandpaper (stock)

Although rarely serious, scarlet fever can trigger complications such as pneumonia, arthritis, and heart and lung disease. 

The scientists worry mutated Strep strains could also cause invasive infections, like the ‘flesh-eating disease’ necrotising fasciitis.

‘The new, more toxigenic strain we have identified has become the dominant cause of more serious Strep A infections,’ joint first author Dr Elita Jauneikaite said.  

Strep A bacteria, like Strep pyogenes, live in the nose and throat. The bacteria spreads via small droplets when an infected person sneezes or coughs.

Scarlet fever is usually mild, with early symptoms including a fever, sore throat and chills.

The tell-tale rash typically appears one or two days later. Starting on the neck, underarm and groin, it eventually spreads over the body, causing small bumps that feel like sandpaper. 

Scarlet fever usually affects children, with outbreaks being common at schools, nurseries and daycare centres. 

Antibiotics can help speed up a patient’s recovery, ease symptoms, prevent the bacteria spreading and avoid serious complications.

Writing in The Lancet Infectious Diseases journal, the scientists noted scarlet fever and other Strep A infections rose in 2016 compared to the previous five years. 

To understand why, they looked at Strep bacteria that circulated in England and Wales over recent years.  

After identifying Strep pyogenes, they found the strains emm3 and emm4 were responsible for the initial surge in scarlet fever in London in 2014. 

During the UK spring of 2015 and 2015, emm1 strains became the main cause of Strep throat.

In spring 2014, only five per cent (five out of 96) of the bacteria collected from Step sufferers in northwest London were emm1, which increased to 19 per cent (28 out of 147) the following year. 

In 2016, emm1 was behind 33 per cent (47 out of 144) of samples. 

Outside of London, 42 per cent (267 of 637) of strains collected in England and Wales in Spring 2016 were emm1, up from 31 per cent (183 of 587) during the same time the year before. 

To investigate emm1 further, the scientists sequenced the genes of all 135 samples collected in northwest London between 2009 and 2016.

They also looked at the DNA of all 552 samples collected in England and Wales during the seasonal spikes of 2013-to-2016. Strep A usually peaks between March and May.

The team assessed the amount of toxins the emm1 strains produced. 

Most of those circulating between 2015 and 2016 were a ‘distinct, breakaway emm1 clone’, called M1UK. 

M1UK had 27 mutations and was associated with increased production of the toxin streptococcal pyrogenic exotoxin A (SpeA). 

SpeA triggers scarlet fever, and may also contribute to Strep throat and some invasive infections, the scientists warn. 

An analysis confirmed M1UK produces nine times more toxin than other emm1 strains at 190 nanograms per millilitre (ng/mL) compared to 21 ng/mL. 

M1UK was in England as early as 2010. 

By 2016, the clone made up 84 per cent of all emm1 samples analysed in England and Wales. 


According to certain scientists of ancient diseases, the Greek founder of Western medicine Hippocrates may have described scarlet-fever like symptoms as far back as the 4th century BCE.

It was first officially identified in 1953 when the Italian doctor Giovanni Ingrassia named it ‘rossalia’ .

The name scarlet fever was introduced by the British doctor Thomas Sydenham in 1676. 

At this time, scarlet fever was considered a mild disease due to its rarity, particularly in comparison to plagues.

Yet, the Industrial Revolution of around the 1820s in western Europe and the US caused population booms that led to overcrowded cities and poor hygiene.

Such conditions caused scarlet fever to thrive, with fatalities rising in the UK from two per cent of cases in the late 18th century to 15 per cent in 1834. 

Squalid living conditions caused the disease to occur in cycling epidemics that did not affect rural areas. 

During the 1850s, Charles Darwin lost two children to the disease, which is also believed to have caused the American author Helen Keller to lose her sight and hearing.

A push for public health and urban cleanliness during the end of the 19th century is thought to have caused scarlet fever cases to tail off. 

Yet, with numbers rising steadily since 2013, experts fear poor nutrition and a fall in living standards may encourage the resurgence of this Victoria-era disease. 

In a second part of the experiment, the scientists compared M1UK with 2,800 emm1 genomes from around the world. They found strains in Denmark and the US had M1UK-like mutations. 

It is unclear whether M1UK could flourish in other countries, with climate and infection management affecting how bacteria take hold. 

However, Strep pyogenes that expressed the scarlet fever toxin SPE A re-emerged around the world in the 1980s.

This caused sepsis, severe soft-tissue invasion and toxic-shock-like syndrome, according to a 1992 paper in The Lancet.

As a result, M1UK should be monitored on a global scale, the researchers stress.

Lead author Dr Nicola Lynskey added: ‘Given that this strain has an apparently enhanced ability to cause all types of Strep A infection, it is important to monitor the bacterium both here and globally.’

However, the team stress M1UK does not appear to have taken hold outside of the UK. 

‘The distinct bacterial clone we have discovered appears so far to be largely limited to the UK,’ senior author Professor Shiranee Sriskandan said.

‘But the fact we have identified two examples of it elsewhere suggests it has the potential to spread internationally and may already be present in other countries.  

‘However, it’s also possible the lineage will not last. 

‘In the past, some lineages have appeared and then disappeared quickly. Only further research on recent strains will provide more insights.’  

Writing in a linked comment, Professor Mark Walker, from the University of Queensland, said: ‘The continuing increase in scarlet fever and invasive disease notifications in the UK exemplifies the essential need to install global surveillance. 

‘We believe the report sends out an important warning for the global public health community – recently emerging scarlet fever strains have enhanced invasive potential which may have profound implications for the future global health burden.’  

Professor Jimmy Whitworth, of the London School of Hygiene and Tropical Medicine, added: ‘This important study gives us a plausible clue to the worrying recent increase in cases of scarlet fever in children in England.

‘The investigators have found a new virulent strain of streptococcal bacteria has emerged, producing nine times the amount of toxin found in other strains.

‘The researchers rightly call for more surveillance to confirm these findings, as these streptococcal infections are highly sensitive to antibiotics, unlike most other types of sore throat in children.’

Professor Whitworth added ‘refining’ existing methods of diagnosing Strep A infections could help GPs identify patients sooner.  

What is scarlet fever and what are the symptoms to look out for?

Scarlet fever is a bacterial illness that mainly affects children. It causes a distinctive pink-red rash.

The illness is caused by Streptococcus pyogenes bacteria, which are found on the skin and in the throat.

First symptoms of scarlet fever include a sore throat and fever which may be accompanied by a headache, nausea and vomiting.

Between 12 to 48 hours after this, a characteristic fine, sandpapery rash develops, often appearing first on the chest or stomach.

Other symptoms include a white coating on the tongue, which peels a few days later leaving the tongue red and swollen (this is known as strawberry tongue).

Cases are more common in children although adults of all ages can also develop scarlet fever.

Individuals who think they or their child may have scarlet fever should consult their GP.

Source: NHS Choices 

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