SARAH Mowat has been plagued by illness for almost all of her life.

The Wangaratta teenager has suffered from reoccurring mouth ulcers, stomach cramps and gastroenteritis.

But it was only just recently that Sarah was diagnosed with a rare form of inflammatory bowel disease known as ulcerative colitis.

Colitis is believed to affect just 13,000 people across Australia, and is an inflammation of the inner lining of the large bowel.

Its cause is unknown, but it has been linked to hereditary influences.

Sarah, 15, suffers from a severe form of the disease, which caused her health to deteriorate rapidly from July last year.

Mum, Kerry Mowat, said they were unaware of the extent of her condition until doctors operated around Christmas time to find most of her large intestine had been eaten away by infection.

"Doctors said it was one of the worst cases they had seen," she said.

"Her intestine was so bad that it just fell to pieces."