Parasitic organisms like protozoa and worms

而某些寄生生物如原生动物和蠕虫
which are - which can cause terrible diseases.

可以引起严重疾病
Malaria is one that causes much disease worldwide.

比如疟疾波及全球患者众多
Schistomiosis, which is a worm that lives in river waters,

血吸虫是一种生存在河水中的蠕虫
causes terrible diseases that

可以引起严重疾病
are still prevalent in many parts of the world.

并仍在世界上众多地区广泛流行
So, just an introduction to the classes of potential

所以我只是简单介绍几类
foreign invaders that our immune system tries to defend us against.

免疫系统试图抵御的潜在外来侵略者
Because it's working to defend us

免疫系统的工作就是抵御
against many different kinds of potential assaults,

不同种类的潜在威胁
the immune system has a diverse repertoire of responses

免疫系统具备类型众多的免疫反应类型
that it uses in the face of these assaults.

以应对各种威胁