Millions of travelers, with trillions of bacteria.
June. The month when the greatest number of Americans travel overseas, many heading off on vacation.
In this month last year, 3.7 million US citizens jetted off to distant countries, and a further 4 million headed for Mexico and Canada.
So it seems as good a time as any to reflect upon some intriguing connections between travel and—yup, you guessed it, bacteria.
Many species of bacteria are motile, moving around under their own steam.
However, although some are capable of moving considerable distances in relation to their size, this is still only measured in micrometers.
Hardly what you’d call traveling.
But it doesn’t prevent bacteria moving around the globe as passengers, of course, and this month millions of air travelers will be ferrying their microbiomes with them as they fly off all over the world.
As a tourist, you may well be helping to distribute microbes around the globe via your gut, lungs, and luggage.
Even the plane itself may be doing its bit to participate in this international “germ trade.”
In 2014, a team from NBC’s Today show tested cross-country commercial flights for bacteria.
Nine out of thirteen of their samples contained what they say were harmful bacteria, and apparently the dirtiest locations they found on planes were tray tables.
A former flight attendant told the TV show that short turnaround times can mean tray tables don’t always get the thorough cleaning they should.
She also recommended, by the way, that you should “carefully check the seat-back pocket before reaching inside, because some passengers will use the air-sickness bag and then return it without telling anyone.”
A perhaps more scientifically robust investigation was carried out by researchers at the University of Limerick in 2015. They analyzed 154 water samples taken from the galleys of two aircraft on multiple days: one long-haul, the other short-haul.
Although they discovered none of the pathogenic bacteria listed in regulatory standards, they did identify 37 different water-borne bacterial species in all, more on the long-haul plane than on the short-haul one.
Although aircrafts are clearly one way for bacteria to move about the world, nature does a pretty good job, too.
In 2006, scientists from the US Geological Survey collected air samples three miles above the middle of the Atlantic.
Over half of the samples contained living microbes that had originated in dust storms blown from Africa.
Genetic sequencing of these bacteria revealed strains capable of causing disease in humans, animals, and plants—and also proved that the mid-Atlantic microbes had come from specific regions in Africa.
More work in a similar vein was carried out by scientists from labs in the UK and Switzerland, using computer-modeling techniques to examine how far bacteria of various sizes could travel around the globe when blown by the wind.
Tiny microbes traveled faster and farther.
What’s more, bacteria could travel widely within the hemisphere in which they were released, but movement between hemispheres was much more limited.
So bacteria released high over South America might spread easily to Australia, but would be unlikely to reach Europe.
Sometimes when humans travel the globe they unwittingly take home souvenirs in the shape of bacteria.
Research conducted in 2014 at Duke University Medical Center in Durham, North Carolina, tracked the gut microbiomes of two individuals almost every day for a full year.
Their bacterial balance stayed remarkably stable, except when rare events brought about radical change.
For example, when one person traveled from the developed to the developing world it led to an almost two-fold increase in their Bacteroidetes/Firmicutes ratio, which was then reversed when the participant went home.
All of which brings us to that all-too common illness affecting those who venture abroad—traveler’s diarrhea.
It spreads easily from person to person, or by consuming contaminated food or water.
And sometimes it’s caused by parasites or viruses, but it is also frequently the result of a wide range of bacteria including E. coli and Campylobacter.
If you’re unfortunate enough to succumb, it’s important to remain properly hydrated, and commercially available oral rehydration salts are an invaluable addition to your travel first aid kit.
However in the hopefully unlikely event that you find yourself suffering from Montezuma’s Revenge with no commercial salts available, it is possible to rustle up your own.
The general consensus for a homemade alternative seems to be this formula: Half a level teaspoon of salt, six level teaspoons of sugar, stirred into one liter (five cupfuls) of clean drinking water, until it’s dissolved.
To be on the safe side, boil the water then cool it.
Finally it’s also worth remembering that in more ways than one, This Too Shall Pass.