 The symptomatic ( <unk> ) chronic stage affects the nervous system , digestive system and heart . About two @-@ thirds of people with chronic symptoms have cardiac damage , including <unk> <unk> , which causes heart rhythm abnormalities and may result in sudden death . About one @-@ third of patients go on to develop digestive system damage , resulting in <unk> of the digestive tract ( <unk> and <unk> ) , accompanied by severe weight loss . <unk> difficulties ( secondary <unk> ) may be the first symptom of digestive disturbances and may lead to <unk> . 
