New Zealand has been exposed to a “worldwide” population of the nasty strep A bacteria, finds a first-of-its-kind study that raises tricky challenges for ongoing vaccine efforts.
New Zealand has been exposed to a “worldwide” population of the nasty strep A bacteria, finds a first-of-its-kind study that raises tricky challenges for ongoing vaccine efforts.
New Zealand has been exposed to a “worldwide” population of the nasty strep A bacteria, finds a first-of-its-kind study that raises tricky challenges for ongoing vaccine efforts.
A common bacteria carried by many people, strep A typically leads to mild throat and skin infections, but can also trigger potentially life-threatening diseases - especially when it turns into its invasive form.
It’s suspected to be involved in 500 such serious cases each year - including between 150 and 200 infections of the debilitating rheumatic fever – while annually costing the health system an estimated $59 million.
As Kiwi scientists work to advance new vaccines to prevent rheumatic fever, public health experts have called for New Zealand to follow other countries to classify invasive strep A as a notifiable disease.
Now, researchers have shed fresh light on how the bacteria circulates here in the form of dozens of different strains, using the same genomic sequencing technology that’s helped pick apart the spread of coronavirus subvariants.
“Strep A is a really diverse bug, with over 200 different strain types described globally,” University of Auckland immunologist Associate Professor Nikki Moreland said.
“Before this study started, there wasn’t a clear picture of how many of these different strain types were causing childhood infections in New Zealand.”
The research has also taken Moreland and her colleagues from Auckland, Otago and Melbourne universities closer to understanding how these strains actually enter the country.
While Covid-19 introduced most of us to genomic sequencing – a process in which scientists decipher genetic material found in an organism or virus – the study’s sampling work was carried out in the 18 months before the pandemic started.
A common bacteria carried by many people, strep A typically leads to mild throat and skin infections, but can also trigger potentially life-threatening diseases - especially when it turns into its invasive form. Photo / Doug Sherring
But Moreland said sequencing the more than 460 strep A strains that caused skin and throat infections in Auckland children over the period wasn’t as straightforward as working with coronavirus samples.
“Because bacteria like Strep A are many times larger than viruses, there’s a lot more data generated – and it’s more complicated to deconvolute what’s happening with it than it is for Covid-19.”
The results revealed 65 distinct strains of the bacteria, illustrating how much more diverse the group is than other pathogens.
“When we compared the Auckland sequences to those identified in other countries, we saw evidence of multiple global introductions of strains, as well as evidence for certain strains then expanding and spreading locally.”
Some of the strains had been commonly detected in Northern Hemisphere countries.
The study confirmed one in particular - M1UK, which has been linked to surges of scarlet fever and invasive strep A infections in England and elsewhere – had been in New Zealand since at least 2018.
“But the overall diversity of strains, and that many different strain types are co-circulating at once, is also reminiscent of what is observed across the Pacific region,” Moreland said.
“Essentially, the sequencing suggests a worldwide population of strep A strains are causing infections in Auckland children.”
When it came to developing vaccines designed to cover all the strains circulating locally – as one $10m project is pushing toward – such data was crucial.
Some “conserved” vaccines under development targeted parts of the bacteria found across all strep A strains, while other “type-specific” vaccines were aimed at combatting only certain strains.
“Given the strain diversity we saw in the study, getting adequate coverage with some of the type-specific vaccines is likely to be challenging,” Moreland said.
“But the sequencing confirmed that conserved vaccines would theoretically protect against all the strains.”
While conserved vaccine candidates held much promise for New Zealand and other countries where there was plenty of diversity, none had yet been tested in clinical trials.
University of Auckland immunologist Associate Professor Nikki Moreland.
“An effective strep A vaccine could prevent rheumatic fever, but progress compared to vaccine development for other pathogens has been slow.”
“In New Zealand, rheumatic fever is notifiable, but the invasive strep A disease is not,” she said.
“In lots of other countries, having invasive diseases be notifiable has helped with disease management and detecting infection surges.
“Without invasive diseases being notifiable in New Zealand, it’s hard to track accurately, and in real-time, if similar events are occurring here.”
With rheumatic fever appearing to be on the rise again here, she said it was critical to understand how the strep A surges occurring overseas may have changed what was circulating here.
“Do we still have the same diversity, have certain strains disappeared, have others arrived?” she said.
“Gaining this data through sequencing will help explain infection patterns and help with disease management and ongoing vaccine development efforts.”
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
