It starts off like an ordinary cold, but it doesn't end like one. Whooping cough, aka the '100-day cough', is a highly contagious bacterial disease that infects millions of people around the world, killing tens of thousands every year.
Fortunately, vaccines to protect us from the Bordetella pertussis bacterium that causes whooping cough have been around since the mid-20th century, shielding people from the intense, sometimes fatal respiratory symptoms. Unfortunately, B. pertussis is not standing still.
In new world-first research, a team of Australian scientists has discovered how B. pertussis strains are adapting to the current acellular vaccine (ACV) used in Australia, which is similar to the ACVs used for whooping cough in other countries around the world.
"We found the whooping cough strains were evolving to improve their survival, regardless of whether a person was vaccinated or not," explains microbiologist Laurence Luu from UNSW.
"Put simply, the bacteria that cause whooping cough are becoming better at hiding and better at feeding – they're morphing into a superbug."
According to the findings, which used a technique called 'surface shaving' to analyse proteins that envelop B. pertussis at the cellular level, the strains studied were seen to be producing more nutrient-binding proteins and transport proteins, but fewer immunogenic proteins, when compared to previous research on the bacterium.
The researchers say these new changes in B. pertussis mean that the bacteria may be "metabolically fitter" than previous generations, and can more efficiently scavenge nutrients from hosts, while avoiding the host's immune system responses.
In addition, because the evolved forms might not trigger immune responses as much, it's possible people could be carrying an infection without realising, since fewer symptoms would show.
"The bacteria might still colonise you and survive without causing the disease," says Luu.
"You probably wouldn't know you've been infected with the whooping cough bacteria because you don't get the symptoms."
The new study builds upon multiple findings made by UNSW researchers in recent years, including the discovery that B. pertussis strains in China were evolving through selection pressure, and that strains without a surface protein called pertactin (targeted by whooping cough vaccines) could have an evolutionary advantage.
It all sounds pretty scary, and the latest research on superbugs in general indicates they're already responsible for sickening 3 million people in the US every year, some 35,000 of which don't survive the infection.
In terms of whooping cough though, the UNSW team says there's no need to panic. B. pertussis is not yet a superbug, and current immunisation medicines still work – but the researchers do emphasise that new vaccines should be developed in the next five to 10 years, to counter the seeming changes underway in B. pertussis.
"Right now the vaccines are still very effective against the current strains," Luu told The Sydney Morning Herald.
"In the future we do need a new vaccine to combat these strains as they continue to evolve."
The findings are reported in Vaccine.