( ( Trichomoniasis ( is ( caused ( by ( the ( single-celled ( protozoan parasite ) ) ) ) ) ) ) ( , ( Trichomonas ( vaginalis . ) ) ) )
(ROOT (S (S (NP (NNS Trichomoniasis)) (VP (VBZ is) (VP (VBN caused) (PP (IN by) (NP (DT the) (JJ single-celled) (NN protozoan) (NN parasite)))))) (, ,) (NP (NNP Trichomonas)) (VP (VBZ vaginalis)) (. .)))
Trichomoniasis is caused by the single-celled protozoan parasite, Trichomonas vaginalis .
(ROOT (S (NP (NNS Trichomoniasis)) (VP (VBZ is) (VP (VB cause) (PP (IN by) (NP (DT a) (NN protozoa))))) (. .)))