Parasites live off a host, so they stand for people, habits or thoughts that drain you. Dream books read them as a sign to notice what is taking more than it gives.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.