Any virus infection, not just those that cause diarrhoea, can cause tummy pain. This is because the bowels are surrounded by lymph glands like those in the neck, groins and armpits and during a general viral illness, they swell too. These swollen glands (the mesenteric glands) can become sore and press on the bowel, so that there is discomfort
and colicky tummy ache, though this is usually less severe than the colic of diarrhoea.
Sometimes the pain of these swollen glands (mesenteric adenitis) is severe enough to mimic appendicitis, and it can be impossible to tell the difference until an operation is done to look at the appendix. In this situation, it is usual practice to remove the appendix even if it is normal, so that it cannot ever cause any trouble (see Appendicitis).