(S (S (S (S (NP (BASENP (DT The) (NN risk)) (PP (TO to) (BASENP (JJ international) (NNS travelers)))) (VP (VBZ is) (ADJP (JJ low)))) (PRN (COMMA ,) (PP (VBG according) (PP (TO to) (BASENP (DT the) (NNP WHO)))) (COMMA ,))) (SBAR (IN because) (S (BASENP (DT the) (NN disease)) (VP (VP (VBZ requires) (BASENP (JJ close) (JJ personal) (NN contact))) (S (VP (TO to) (VP (VB be) (VP (VBN transmitted))))))))) (PERIOD .))