Vaccine for 'traveller's diarrhoea' in the offing

In an effort to develop a preventive vaccine against traveller's diarrhoea, scientists have discovered how the bacteria behind the disorder works to cause infection.

Researchers, including those from the University of Georgia in the US, analysed samples taken directly from citizens who volunteered to become infected with the bacteria called Enterotoxigenic E coli, or ETEC, a major cause of traveller's diarrhoea.

"If we can understand how ETEC causes disease, we can develop new vaccines to prevent infections," said Stephen Trent, a professor at the University of Georgia.

Ingesting contaminated food or water can lead to ETEC infection, which can cause diarrhoea for up to a week, according to the study published in the journal Proceedings of the National Academy of Sciences.

Considering the fact that up to 200 million people become infected annually, an estimated one billion days of human productivity are lost every year due to ETEC infections, researchers said.

Visiting the doctor to get vaccinated before a trip can prevent travellers from catching a disease, they said.

There are no available vaccines to prevent ETEC infections, so travellers must constantly be concerned about what they eat and drink while on vacation.

The group examined how ETEC behaved inside humans during infection compared to how it behaved in the laboratory.

They were surprised to find that ETEC produced more toxins when grown in the laboratory than it did in human infection samples.

The researchers discovered that ETEC could sense oxygen in the atmosphere, and that controlled the amount of toxins produced by ETEC.

There is more oxygen in the atmosphere than there is in the digestive tract, which resulted in the differing levels of toxin expression, they said.

The finding gives researchers hope that they have identified the "cue" that ETEC uses to determine when to make toxins that cause disease.

Previous groups have identified numerous factors that contribute to toxin production in ETEC, but this is the first-time oxygen has been identified as a major player in ETEC virulence.

"We think ETEC can sense the oxygen given off by our own cells as a cue to produce toxins," said Alex Crofts, a graduate student at the University of Texas in the US.

The group now hopes to use this oxygen-sensitive ETEC response against the bacteria to prevent infections.

"Beyond toxins, we found ETEC regulates many other factors in response to oxygen, and some of those are promising new targets for future vaccines," said Trent.

"ETEC is a global burden on society, and we are doing all we can to advance our understanding of the disease," he said.