If in London rats have turned to two-feet-long mutants on a feeding frenzy of household waste and fast food scraps, in Australia, experts are battling something microscopic. So far, it has been bad news as experts have found out the bacteria causing whooping cough have evolved.

The most likely culprit in the mutation of the Bordertella pertussis, the bacterium causing whooping cough, is the vaccine used to protect humans against it. The vaccine has been effective by zeroing in on pertactin, a protein that plays a major role in the development of the illness. The other two vaccines used in the country target other surface proteins known as filamentous hemagglutinin and pertussis toxin.

"It's like a game of hide and seek. It is harder for the antibodies made by the body's immune system in response to vaccination to 'search and destroy' the whooping cough bacteria which lack pertactin. This could mean that these pertactin-free strains have gained a selective advantage over bacterial strains with the pertactin protein," said Ruiting Lan, senior author of the latest study on whooping cough and associate professor at School of Biotechnology and Biomolecular Sciences at the University of New South Wales.

The team of experts, led by UNSW PhD candidate Connie Lam, have looked into cases of whooping cough from across Australia and have found out that roughly 80 percent of the cases in 2012 were due to strains of the bacterium that do not have pertactin.   

"The fact that they have arisen independently in different countries suggests this is in response to the vaccine. More studies are needed to better understand the effects of vaccination on the evolution of the organism," Lan added.

The researchers have analyzed 320 samples of bacteria from whooping cough patients in the states of Western Australia, South Australia, Queensland, Victoria and New South Wales. The latest number shows a big jump from five percent in 2008 to 78 percent pertactin-free strain in 2012.

Australia battled with whooping cough epidemic during the said period with around 142,000 documented cases with nine babies that succumbed to the illness. Experts recommend immunization of babies at six weeks to two months, between four and six months and a booster at four years old.

However, the researchers want to clarify that it does not necessarily mean that the pertactin-free whooping cough bacterium strain is more dangerous than other strains. They also do not know if the decreased effectiveness of the vaccine will be just for the short-term or for the long-term.

"Vaccination is still the only way to protect against whooping cough, especially for the youngest babies who are most at risk of severe illness," Lan said.

The findings are consistent with other studies conducted in other countries such as the United States and France so the threat of pertussis cough is not limited in Australia.

The study titled "Rapid Increase in Pertactin-deficient Bordetella pertussis Isolates, Australia" appears in the journal "Emerging Infectious Diseases."

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