If you are a short-term traveler, this question may not be relevant, but for long-term travelers or expats, knowing whether immunity from foreign bacteria can be “earned” is an important topic. We have written about traveler’s diarrhea, probiotics, and various parasitic infections on this site, but we have not talked about whether exposure, particularly long-term exposure, can lead to immunity.
A lot happens in the early years of life
The bad news for those expecting to cash in their hard earned travel time for immunity to traveler’s diarrhea is that most of our gut bacteria is already established at a young age. As a traveling adult, there is not much you can do to transform the contents of your GI tract. While it’s true that taking probiotics may have an impact, whatever positive effect they have will not stand up to a full scale invasion of foreign bacteria.
But I thought that long-term exposure to bacteria will grant immunity?
It’s true that your immune system is pulling most of the weight when it comes to fighting unwelcome bacteria in your gut. It’s not a legion of yogurt molecules that are coming to your rescue. The immune system does have a tendency to transform its victories into future prevention and while exposure certainly can increase your chances of resistance, it all depends on the nature of the bacteria and the level of contamination. There may also be contradicting evidence on this front. For example, in this article, there are two conflicting lines:
1. “Because the travelers have never been exposed to the pathogens, they have been unable to gradually develop immunity.”
2. “Although there is still a risk of illness occurring in subsequent weeks and for up to 2 years even after episodes of traveler’ diarrhea [21, 33], it appears that some immunity is gradually developed”
In other words, you can possibly count on some small level of immunity but you certainly shouldn’t bank on it. Another way of thinking about this: no, it’s not a good idea to deliberately eat contaminated food and water in an effort to accelerate the onset of an immunity that may never come.
So what should you do?
If you can’t count on developing any immunity (or if the immunity is relatively insignificant), then why not just load up on the antibiotics? Well, here’s the thing. While you may not be able to build up immunity to foreign bacteria, you do have an army of good bacteria in your gut going out about its business. Their job is to “somewhat inhibit toxic microbes from getting a foothold or flourishing, even if they cannot fight off a full-scale assault.”
As usual, the best strategy is one of balance. As we wrote in our article on traveler’s diarrhea, you want to be careful about your diet, but also your treatment. An overly aggressive treatment strategy will not serve you well in the long-run especially if your traveler’s diarrhea is just a mild case. Head over to the article and refresh yourself on what is a very important topic for any traveler. Yes, go spend some more time reading about diarrhea.
Photo credit: newhealthguide.org