eli5: How does a stomach bug affect the body?


My kids and I got the stomach flu: vomiting, diarrhea, and then body aches/fevers. Why does this cause stomach distress? Does it affect our gut biomes such that we can’t keep food down/digest it? Or something else?

In: 5

A stomach flu – in medical terms, a case of *gastroenteritis* – is the name for inflammation of the stomach and intestines (hence *gastr(o)-* “stomach” + *enter(o)-* “intestines” + *-itis* “inflammatory condition”).

Most cases are caused by viruses in your food. In adults, the most common is [norovirus](https://en.wikipedia.org/wiki/Norovirus). This virus can survive the environment of your stomach and reach your small intestine, where it infects cells and begins to reproduce. This triggers an immune response from your body, which (a) activates your immune system and (b) causes your body to try to “flush” your digestive tract to get rid of the infectious agent.

To get whatever is harming you out, your body triggers your vomiting reflex (removing any contaminated food from your stomach) and pumps extra water into your intestines (flushing any contaminated food out as diarrhea). That accounts for the vomiting and diarrhea. The fever and aches are general symptoms of an inflammatory response throughout your body, which is why they’re symptoms of most illnesses. They’re part of your body’s general response to sickness, which is to ramp up your immune system and trigger lots of adaptations that make your body more hostile to bacteria (like a change in body temperature and removing free iron from your blood).