Hi and welcome to HCM. Thanks for the query.
It sounds like infectious enterocolitis and it may be severe. The most important thing is to prevend dehydration
see he must drink plenty of fluids even if he has intensive diarhheas. But i think he needs to visit doctor since there can be some inflammatory colitis
active tumours. He should do red blood count and stool analysis first.
Wish you good health. Regards