The tornado symbolizes some kind of destruction in our waking life, therefore we feel a lot of panic and confusion. The dream could be hiding some very important and special message. If emotions are negative or the dream ends badly, then such dream reflects the fear of events in our waking life that we are unable to overcome and can bring us loss of property, friendships and even an accident.
Dream dictionary: sent to deliver a message to a prominent man dream meanings
Any kind of the parasites bring unpleasant feelings, because it shows the minor problems that causing much of the stress. Consider that your body could send some message about your general health, therefore make sure you check yourself up.