( STIs ( ( are ( diseases ( caused ( by ( pathogens ( that ( spread ( through ( sexual contact ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS STIs)) (VP (VBP are) (NP (NP (NNS diseases)) (VP (VBN caused) (PP (IN by) (NP (NP (NNS pathogens)) (SBAR (WHNP (WDT that)) (S (VP (VBN spread) (PP (IN through) (NP (JJ sexual) (NN contact))))))))))) (. .)))
STIs are diseases caused by pathogens that spread through sexual contact.
(ROOT (S (NP (NP (JJ Pathogens) (NN spread)) (PRN (-LRB- -LRB-) (PRP s) (-RRB- -RRB-))) (VP (VBZ stis) (PP (IN during) (NP (JJ sexual) (NN contact)))) (. .)))