Environment not mutations drive bacterial epidemics

Scientists had always thought that bacterial diseases like Meningitis and the Plague survived and developed because of mutation but new research shows that they may have been able to do so because of the environment.

A new study published this week shows that instead of gaining genetic advantage by quickly tweaking their DNA, viruses continue to develop in physical environments, through insect carriers, and even in the human body.

The study focused on Typhoid fever, a disease which is still responsible for 200,000 deaths and upwards of 27 million cases of illness per year. International travellers, especially those visiting developing countries where it's common, are prone to ingesting the bacteria through contaminated food and drinks.

Researchers were able to piece together its genetic family tree by looking at the evolutionary history. Turns out that the virus originated some 450 years ago and has not changed as was expected.

Even though seven distinct lineages had evolved, the bacteria didn't genetically change to become more contagious or more efficient at causing illnesses in humans.

Mark Achtman, a microbiologist at the University of Warwick says changes in the immediate environment that these pathogens are surrounded in really play a role at how successful they are at spreading and causing outbreaks in their hosts.

“This implies that many epidemics and pandemics of bacterial disease in human history reflected chance environmental events, including geographical spread and/or transmission to naïve hosts, rather than the recent evolution of particularly virulent organisms,” Achtman said in an interview with Yahoo Canada News.

Achtman said the viruses could have survived by hiding out in biting insects like ticks to spread between hosts or even lurking in bodies of water or soil.

“For pathogenic bacteria, their environment may consist of the host they are infecting and all of the differences between hosts due to their immune status and general health.

“They may even spend some part of the infectious cycle in competition with other microbes and viruses, for example in the intestine or oral cavity. These are also part of their environment.”

Leading theories on why certain viruses become so aggressive were instead centred on bacteria gaining a genetic advantage through quick evolution by tweaking its DNA.

“When epidemics break out, many scientists suspect they have been driven by increased virulence or fitness, possibly associated with the gain of novel genes or mutations,” Zhemin Zhou, co-author of the new study, from Warwick Medical School said in a press statement.

“We wanted to trace genetic changes in a prominent bacterial pathogen back to see if this was true.”

But exactly how certain bugs end up being killers in only some humans while not in others is still a mystery that leaves researchers baffled.

Scientists have identified the exact species of bacteria that causes epidemics of cerebral meningitis but only a small proportion of the individuals who are exposed to the bacteria show signs of illness. The rest don't know they are healthy carriers of the bugs in their noses and throats.

“The differences between humans who remain healthy and those who become sick remains unexplained,” Achtman said.