Hello and Welcome to ‘Ask A Doctor’ service.
I have reviewed your query about your Brother and here are my thoughts.
The commonest causes for the symptoms that your brother has like
body ache, mucus in stool, anxiety can be due to severe colitis.
Can be IBS that is
irritable bowel syndrome as anxiety can cause IBS which in turn causes body ache and mucus in stool.
Sort of
gastroenteritis.
This can be found out by the following ways step-by-step:
Send the stool and blood for tests and if infection is present then he will be given a course of an antibiotic,
metronidazole and probiotics along with symptomatic treatment as needed.
This may cure his problems.
If there is no relief after this then he needs further clinical evaluation, examination and investigations under the care of a Gastroenterologist.
Ultrasonography/CT scan of abdomen.
Colonoscopy and whatever is advised.
If all the tests are normal then this may be related to IBS and control
of stress controls other symptoms too.
If a specific cause is found then he will receive a specific treatment.
Hope I have answered your query.
Let me know if I can assist you further.