1) Homeostasis describes the carefully maintained optimal physiological conditions in our body, regardless of our outside conditions. Viruses can disturb this homeostasis by growing in our body, where they do not below, and producing toxins. Viruses are very much like the effect of a storm at sea on a sailing ship, as the ship is unable to rect as normal to feedback controls to maintain a course.
2) The feedback loop in a sailing ship to maintain it's course would be the ships captain checking the course and detecting that the ship is off course, giving a signal for the ship's rudder and sails to be adjusted. The wind that first pushed the ship off course then plays a role in bringing the ship back on course.