The dengue virus consists of 4 strains: DENV-1, DENV-2, DENV-3, and DENV-4. For all strains, the female mosquito is the leading carrier. As a mosquito bites a person who is already suffering from dengue fever, the virus gets stored in the stomach and saliva glands of the insect. After an incubation period of 12 days, anyone who is subsequently bitten by that same mosquito may contract the virus through the bite.

Dengue fever patients who have contracted one type of the dengue virus will become immune from this strain; however, should they come into contact with a different strain of dengue, then they will again suffer from the symptoms of dengue fever — which are often more extreme the second time around.

Dengue fever symptoms include fever, headache, aching eye sockets, general aches and pains, joints or bones aches, and a rash resembling heat rash, with some cases experiencing bleeding such as nose bleeds or bleeding gums.

As for dengue hemorrhagic fever, symptoms include all the symptoms of dengue fever, but with specific additional symptoms including:

1. A fever over 38 degrees Celsius for over 2-7 days
2. Nausea, vomiting, and a loss of appetite
3. Flush face, small red spots on the skin, or bleeding found in various areas such as nosebleeds, scurvy, and blood in urine or stools
4. Severe stomachache, which increases in pain if pressure is applied
5. In certain severe cases where a patient has suffered from a fever for 2-7 days, they may also suffer from some blood circulation issues or go into shock, which is known as dengue shock syndrome. Symptoms include restlessness, cold toes or fingers, infrequent urination, decreased blood pressure, and an unmeasurable pulse.

Treatments are according to the symptoms, generally there is no antiviral for dengue fever itself. Fever will last 2-7 days. Drink adequate hydration. Avoid drugs that contain aspirin or NSAIDs which can increase the risk of bleeding.