Physical barriers to entry of microbes Before a microbe or parasite can invade the host and cause infection,it must first attach to and penetrate the surface epithelial layers of the body.

• 微生物侵入的物理屏障微生物或者寄生虫侵入宿主并引起感染之前，它必须先附着并穿透宿主机体表面的上皮层。