If you dream of parasites on someone, it means there are people taking advantage of this person.
Another dream interpretation could be the presence of a disease in that person. This translates to parasites which are eating into the person.
You may have seen visual clues on that person. Your gut feeling (intuition) may have alerted this to you. Then your brain created a dream to reinforce the message. Its up to you to see if you will take any action on this.