What is the real nature of germs? Well, here we come to a subject essential for human life. When we see the air around us filled with different species of birds and the water filled with fishes, when we observe the life forms that creep along the earth and others frolicking on it and revealing themselves to our senses, we are looking at beings we can correctly describe as creatures of the developing Godhead in one form or another, even if they are occasionally harmful.
But in the case of germ-like creatures resident and active in other living beings, in plants, animals, or humans, we are dealing with creations of Ahriman. To understand the existence of such creatures correctly we must know that they express spiritual facts, namely the relationship between human beings and Ahriman. This relationship is established through a materialistic attitude and purely egotistical states of fear. We see the conditions allowing the existence of such parasitic beings correctly if we realize that they are a symptom of Ahriman intervening in the world.
Source: Rudolf Steiner – GA 154 – The Presence of the Dead on the Spiritual Path: LECTURE THREE: AWAKENING SPIRITUAL THOUGHTS – Basel, May 5, 1914
Translated by Christian von Arnim and edited by Joachim Reuter