Ew. Well, there are a lot of causes for diarrhea (viral infection, autoimmune attacks, and alcohol being the primary ones in North America), and almost as many for vomiting, but I think I can make a quick post on a few causes…eventually. >_>
At least you don’t have dysentery?
Anyway, yeah, you’re about right, when viruses cause vomiting and/or diarrhea, it’s often due to direct attack to the guts. Norovirus is a gastroenterovirus, meaning it affects the small intestine and stomach.
The thing is, it’s impossible to cultivate noroviruses in the lab, and we don’t *know* if there are enterotoxins coded by the noroviruses (which cause a non-inflammatory but very angry response by the immune system on the intestine), like rotaviruses do. They’re doing something to the intestines, obviously, but the cause for the violent projectile vomiting (as compared to just, like, regular puking in other gastroenteritises) and diarrhea isn’t completely understood.
We just know that yes, it’s a response to an attack on the gut cells - maybe a direct attack, maybe a toxin affecting them, something like that. What’s sort of weird about norovirus is that there are very few infected cells in the intestines, and the Peyer’s patches (kinda like intestine lymph nodes, they release and house immune particles) aren’t activated/affected except in immunocompromised people. Yet the gut is obviously very angry, and people around the world die from dehydration due to these viruses every day.
For anyone into virology or immunology, TWiV did a podcast on Noroviridae back in 2011 and while we know a wee bit more about the animal noroviruses today, our knowledge on human norovirus hasn’t made any huge leaps forward since then.