 The human disease occurs in two stages : an acute stage , which occurs shortly after an initial infection , and a chronic stage that develops over many years . 
 The human disease <a href='uninflect' title='1'><mark>occurs</mark></a> in two stages : an acute stage , which <a href='uninflect' title='2'><mark>occurs</mark></a> shortly after an initial infection , and a chronic stage <a href='null_relcl' title='3'><mark>that</mark></a><a href='uninflect' title='4'><mark>develops</mark></a> over many years . 
The human disease occur in 2 stages : an acute stage , which occur shortly after an initial infection , and a chronic stage develop ova many yrs .