Strep A immunity is possible without getting sick

Exposure to a mild or symptom-free strain of Streptococcus pyogenes (Strep A) can trigger the body’s immune response and naturally build protection, potentially solving a nearly 100-year-old mystery of immunity.

New Griffith University research, with the help of clinical scientists from the Murdoch Children’s Research Institute (MCRI), investigated how immunity developed over time as infection rates declined with age, suggesting progressive immune protection.

Strep A is a common bug which can cause painful tonsillitis and school sores in young children and teenagers.

If untreated, it can lead to rheumatic fever, rheumatic heart disease and kidney disease, conditions for which First Nations peoples in Australia suffer some of the highest reported rates in the world.

It is estimated 10-20 per cent of children across Australia develop Strep A tonsillitis each year, with some getting the disease multiple times and requiring surgical removal of the tonsils.

By adulthood, most people have developed immunity to Strep A even though most will have only had a few bouts of tonsillitis in their life.

Senior author Associate Professor Manisha Pandey from Griffith’s Institute for Biomedicine and Glycomics said: “How this might happen has never been adequately explained as there are more than 250 distinct strains of Strep A, and immunity to one strain does not provide protection against the others.”

“To address this question, the team investigated the development of immunity using samples collected through a controlled human infection study conducted by MCRI researchers who administered a dose of Strep A which was high enough to cause tonsillitis in most, but not all.

“All participants were treated with antibiotics, regardless.

“Surprisingly, antibodies from the asymptomatic participants not only bound strongly to the exposed strain of bacteria but were able to kill the Strep A germ in a murine model of tonsillitis.”

The findings demonstrated both symptomatic and asymptomatic participants developed robust immune responses to the Strep A strain they were exposed to.

Dr Ailin Lepletier, said it had been known for many years that multiple strains of Strep A were circulating in the community and up to 30 per cent of people had Strep A in their throats without getting sick.

“But we didn’t know this may be providing immunity to these strains, causing silent infections so that by adulthood, we have accumulated antibodies to fight most strains,” she said.

“While a person may not feel sick, their body can still learn how to fight the bacteria and remember it from childhood into adulthood.”

Professor Michael Good AO, said this mechanism of natural immunity may also apply to other common infections.

“While highly intriguing for Strep A, it is unlikely to provide a strategy for a vaccine as it would be necessary to vaccinate against each of the 250 strains,” he said.

Dr Anna Calkin, National Manager of Research at the Heart Foundation, said the findings came from research made possible through approximately $2.79 million in Heart Foundation funding.

“The findings highlight the importance of investing in research that addresses conditions disproportionately affecting First Nations peoples,” Dr Calkin said.

“By improving our understanding of how natural immunity to Strep A develops, this work may contribute to future efforts to prevent rheumatic heart disease and close longstanding health gaps.”

The research team included Griffith University Professor Daniel Kolarich, plus MCRI researchers Associate Professor Joshua Osowicki and Professor Andrew Streer.

The paper ‘Subclinical exposure to Streptococcus pyogenes drives the development of long-lived homologous immunity’ has been published in Nature Communications.

UN Sustainable Development Goals 3: Good Health and Well-being