梅毒 (ばいどく, 'syphilis') is the medical term — 梅 ('plum') + 毒 ('poison'), from the plum-like sores the disease causes. 性行為を通じて ('through sexual acts') uses ~を通じて for 'through, by means of.' 感染する ('to become infected') is the standard medical verb. A medical information sentence.