Scarlet fever: New bacterial, "fitter"  strain discovered

A team of English scientists has discovered a new strain of group A streptococci. In her opinion, she is responsible for the significant increase in invasive scarlet fever, which was observed in 2016 in England and Wales.

Scarlet fever is an infectious disease caused by group A streptococci (Strep A) and typically affects infants. The bacteria release pyrogenic exotoxins (scarlet fever toxins) in the body, which are responsible for the disease symptoms. These include sore throat and skin rash, and in very rare cases, invasive diseases in which the bacterium enters the bloodstream or tissue and can cause sepsis and toxic shock. The infection, which reaches its peak in the spring, can be treated well with antibiotics.

Drastic increase in scarlet fever
A research team from Imperial College London, the University of Sheffield , Public Health England and the Wellcome Sanger Institute is currently reporting in the journal The Lancet Infectious Diseases on a new strain of group A streptococcus, which they consider to be the main cause of the increase in Strep-A Inspections. In 2014, 15,000 cases were reported in England, more than 17,000 in 2015 and more than 19,000 in 2016. In addition, in the spring (March to May) 2016 there was a 1.5-fold increase in laboratory confirmed invasive Group A streptococcal infections compared to the previous five years.

Increase in emm1 infections
Researchers looked for a possible link between overall scarlet fever and the increase in invasive forms. For their analysis, they used bacterial strains of infection between the spring periods of 2014 and 2016 collected by the Imperial College Infection Biobank throughout northwest London and identified the main genetic subgroups. These are termed "emm" due to a gene type transmitted by the bacteria. The London data showed that most of the cases in 2014 were caused by the strains emm3 and emm4, but the infections with the emm1 strain increased year-on-year. In 2014, they were responsible for only 5 percent of the cases, in 2015 for 19 percent in 2016 for 33 percent.

M1UK identified
This suggests, according to scientists, that the emm1 subgroup has changed in some way and may have become "fitter". In a genetic analysis, they uncovered a new strain type within the group that differed from the other emm1 strains by 27 genetic point mutations. Some of these are in genes that may be involved in toxin production. Further experiments revealed that the new strain actually produced nine times more streptococcal pyrogenic exotoxin A (SpeA) than other emm1 strains, increasing the likelihood of causing strep throat and scarlet fever and leading to an increase in invasive infection. The researchers named the new strain M1UK.

High proportion of M1UK in all emm1 infections
Afterwards, the scientists wanted to know how often the new strain was represented in the emm1-invasive Strep A infections of the investigation periods. The results of 552 samples showed that 77 percent of cases of invasive disease caused by emm1 Strep A in England and Wales in the spring of 2016 were due to the newly identified M1UK strain. The analysis of all emm1 strains (1240) from invasive disease cases in Great Britain over a period of ten years resulted in an 84 percent share by 2016. The team also analyzed 2800 Strep A genome sequences from around the world and found individual cases of M1UK in Denmark and the US.

Call for global vigilance
"There is still uncertainty about the cause of the scarlet rise," says Elita Jauneikaite, first author of the study at Imperial College London. "It could also be a consequence of changes in practice, the population or environmental factors. Research is currently underway to find ways to best reduce the burden of Strep A infections, including the development of a vaccine. "We may also need to consider whether the guidelines for the diagnosis and treatment of cervical infections need to consider the development of new strains and complications such as scarlet fever and invasive infections," says Jauneikaite.

The team emphasizes that the new strain is easily treated with antibiotics, but nevertheless calls for global vigilance to identify other cases of the strain in other countries.