Researchers in the UK and Europe have discovered the bacteria which causes whooping cough can “lurk silently” in the noses and throats of healthy people.
It is the first time scientists have confirmed a person can live with the bacteria – Bordetella pertussis – without becoming unwell, meaning they could unknowingly transmit the infection to other individuals.
The discovery, made by a team based at University Hospital Southampton, explains why clinicians across the world are seeing an increase in sporadic outbreaks of the condition.
What is whooping cough?
Whooping cough, also known as pertussis, is a highly-contagious bacterial infection which is spread through the coughs and sneezes of an infected person.
It causes repeated coughing that can last for two to three months or more and affects around 16 million people every year worldwide, particularly in developing countries, causing around 200,000 preventable deaths in children.
There were 25,891 cases diagnosed in the UK between 2012 and 2018 compared to 6,216 between 2005 and 2011 – a four-fold increase.
Adults suffer a milder form of the disease compared to young children but can still have an unpleasant cough for up to three months, while babies under the age of six months can be vulnerable to severe and life-threatening complications.
Spread unknowingly
Although a vaccine is offered to all babies in the UK – where 18 have died as a result of the infection since 2012 – it does not offer lifelong protection and is now less effective than it was 15 years ago.
This is why the Southampton discovery is so significant – it means the bacteria can spread from person to person, silently, and cause disease in those who are not immune, including babies, and those not vaccinated.
The researchers at UHS, led by Professor Robert Read, inoculated 34 human volunteers with Bordetella pertussis via nose drops and monitored them in a research facility for 17 days.
They assessed their immune responses before giving them an antibiotic to clear the infection.
The results, published in the journal Clinical Infectious Diseases, showed participants could be safely infected without developing symptoms and cleared of the bacteria within two days.
“The study showed that the bacterium which causes whooping cough can lurk silently in the nose and throat of even healthy members of the community,” explained Prof Read, who is director of the NIHR Southampton Biomedical Research Centre.
“This is extremely important as it explains why we are seeing episodic outbreaks of whooping cough throughout the world, with serious disease occurring in those people who are not vaccinated or who had their vaccines a long time ago.”
The £2.3 million study forms part of a wider £24 million European project, PERISCOPE, funded by the Bill & Melinda Gates Foundation and the Innovative Medicines Initiative (IMI), involving experts from 22 institutions across 11 countries.
Prof Read added: "In future work, the team will be able to learn more about what protects people from infection and will be able to test new vaccines and strategies to prevent whooping cough."