Bye bye Delhi belly

In Mexico it is known as a bout of Montezuma's revenge, in India a case of Delhi belly. But whatever it is called, it is common. An estimated 50-60% of the 50 million travellers who visit some of the world's more exotic holiday spots each year come down with what public health officials know rather less colourfully as traveller's diarrhoea.

But could the era of spending several days of a long-awaited and expensive holiday seeing nothing more interesting than the toilet walls soon be over? Results announced this week from a clinical trial of a new vaccine against the most common cause of traveller's diarrhoea suggest that they might.

In the trials at St George's Hospital in London, a single dose of the new oral vaccine was enough to trigger significant activity in the immune system of half of the 36 volunteers. With two doses this rose to 70%. That may not sound particularly effective, but it is already as good as some vaccines in use, including those that offer protection against typhoid.

"The results exceeded our expectations and pave the way for the development of a whole new generation of oral vaccines that are safe, easy to administer and effective," says Dr Steve Chatfield, chief scientific officer at Microscience, the biotechnology company that developed the vaccine. The vaccine is still several years from being made widely available, but its developers believe it will eventually be popular among everyone from holidaymakers to service personnel stationed overseas. "This illness affects international business and leisure travellers, resulting in missed meetings at high cost to company budgets and ruined holidays," Microscience says.

Travel health experts agree there is a demand for protection from the worst that foreign climes can throw at our sensitive digestive systems.

"Bacterial forms of traveller's diarrhoea are the most common travel-related ailment by far, so a vaccination would be very good," says Michelle Abbott, a nurse with the Medical Advisory Service for Travellers Abroad, in Leeds.

Although there are rarely any long-lasting effects, the disease can trigger irritable bowel syndrome in a few cases. Several other companies around the world are developing similar vaccines and a new oral vaccine against cholera also guards against some of the most common bacteria.

But the new vaccine may not be as useful as some hope, says Ron Behrens, a travel medicine expert at the London School of Hygiene and Tropical Medicine. "I don't think there's much use for them in so much as they have a very small impact on quite a common problem. The actual benefit in reduced illness is not that huge," he says. "There are hundreds of different organisms that can cause traveller's diarrhoea that would not be affected by a specific vaccine."

The new Microscience vaccine - called spi-VEC - is targeted to fight infection by a common bacteria called enterotoxigenic E Coli (ETEC). The vaccine is actually made from salmonella bacteria, rendered harmless by the removal of several important genes. Key chemicals from ETEC are added to fool the body into generating antibodies against it. Each dose of vaccine is expected to offer about six months' protection.

Although diarrhoea among people in the developing world kills 500,000 a year worldwide, traveller's diarrhoea is clearly not as serious a problem as many diseases that vaccinations have been used to target, such as polio and smallpox.

"Most of the new vaccines that are being developed tend to be ones that can be sold to western travellers, where the money is. I don't always think they match global needs," says Behrens.

David Tough, assistant scientific director of the Edward Jenner Institute for Vaccine Research, says the work is part of a new wave of vaccine research. "There are a variety of different approaches that are being tried to generate better vaccines," he says. "Historically the biggest successes have been against viruses but there certainly is a need for vaccines against bacteria, because resistance to antibiotics is becoming a major problem, and vaccination is being looked at now as more of an alternative."

Despite the trend towards developing vaccines against "inconvenient" money-spinning conditions, a lot of work remains targeted against the major killers, including HIV, malaria and tuberculosis. The current TB vaccine has been around for almost a century and is widely administered. But the resurgence of the disease in recent years has raised fears that the vaccine does not protect into adulthood. Last month the Bill and Melinda Gates Foundation donated $82.9m to the search for a replacement

Tough says researchers are also considering novel ways of administering vaccines besides the standard jab. "Immunisation in the nose is something that's being looked at," he says. "It may actually generate a better immune response as many of the infections we get enter through the nasal cavities." Evidence suggests that generating an immune response through a spray in the nasal tissues may be more protective than injecting into the muscle.

"With things like influenza, there may be an improvement if you vaccinate that way," Tough says.

Flu remains one of the most difficult viruses to develop an effective vaccine against, because the illness is caused by dozens of different strains that readily mutate. Research into a vaccine against the common cold has stalled for the same reason. Each version of the cold virus carries its own antigens, the substances that induce the formation of specific antibodies. So you might soon be able to enjoy a more comfortable holiday, but winter colds will remain as miserable as ever.

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