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27 May, 2019 - 16:04 By Kate Sweeney

Cornering a killer: Strep A vaccine closer after Cambridge-Oz research

Wellcome Sanger’s lead author Dr Mark Davies (Picture courtesy Peter Casamento)

The quest for a global vaccine to fight potentially lethal Strep A infections has taken a major stride forward after Cambridge and Australian researchers sequenced the DNA of more than 2,000 Group A Streptococcus samples from around the world.

Researchers from the Wellcome Sanger Institute, the University of Cambridge, the Peter Doherty Institute for Infection and Immunity (Doherty Institute) in Australia, and the University of Queensland, Australia, revealed the differences between strains from more than 20 countries and identified potential vaccine targets present across most strains.

Published today in Nature Genetics, the 10-year project found there were some molecular targets present in bacterial strains from all 20 countries embraced in the study – including the UK, Australia and India – which point to the possibility of developing an effective vaccine against the bacteria.

Group A Streptococcus bacteria is one of the top 10 causes of death from infectious diseases worldwide. It is estimated to cause more than half a million deaths a year, mainly in low-income regions of the world.

It can cause many different infections, ranging from Strep throat, which is widely seen in the developed world, to scarlet fever and rheumatic heart disease, which are constantly present and considered endemic in lower-income areas of the globe.

At present there is no effective vaccine for Strep A and the search is hampered by the variety of Strep A strains. Until now, most of the information has come from high-income areas such as the UK and US but very little is known about Strep A in the low-income areas of the world where it causes the most problems. This means that current vaccine candidates may not be effective in all areas.

To remedy this, the researchers collected more than 2,000 samples of Strep A from 22 countries around the world, including countries in Africa and the Pacific, New Zealand and Australian Aboriginal communities.

By sequencing and analysing the DNA of each sample, they were able to determine the genes present in each strain, and see the variety in strains across the world.

The project found that current leading vaccine candidates would have limited coverage in the low-income areas where Strep A is endemic and the vaccine is most needed.

Dr Mark Davies, lead author from the Wellcome Sanger Institute and University of Melbourne’s Doherty Institute, said: “Using large-scale genomic sequencing, we identified the existence of more than 290 genetically different lineages of clinically important Strep A, highlighting the challenges of designing an effective global vaccine.

“However, using all the data we collected, we narrowed down common genes in almost all strains of Strep A globally. This is a tremendous step forward in identifying what may work as a global vaccine candidate.”

Professor Gordon Dougan, an author from the Wellcome Sanger Institute and University of Cambridge, added: “Millions of people around the world are affected by Strep A. It can cause a range of conditions, from sore throats and outbreaks of scarlet fever in the UK, to infections leading to rheumatic heart disease in populations such as the Australian Aboriginal population.

“In addition to aiding research into a vaccine, genomic data from our study will help researchers understand how Strep A causes disease and why it is different in high-income areas to endemic regions.”

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