Diarrheal diseases can always occur. You travel to foreign countries and perhaps eat foods that your stomach is not used to. That does not mean that the food itself is bad! Add to this a new environment and the time difference that can potentially upset your digestive system. Travel sickness is often a companion. If you do not like bus travel very well, especially on winding roads, we recommend that you take appropriate drops or tablets with you.
If you would like to learn more about country-specific diseases and prevention or precautionary measures, we recommend a look at the page of www.fit-for-travel.de.