Dengue fever affects the body by causing a high fever and flu-like symptoms. The virus infects your blood and causes a migraine-like headache, rash, achiness, queasiness, tiredness and fever. It can affect the blood, causing mild bleeding of the gums, and you may bruise easily. Once you have recovered from dengue fever, antibodies are left in your system, making your reaction to the disease more severe if you are infected a second time.