Regular flu may be due to a simple viral or bacterial infection, amongst other possible causes. Dengue is a more dangerous form and needs a hands-on approach. The World Health Organisation says, "Dengue is a viral infection transmitted by the bite of an infected female Aedes mosquito. There are four distinct serotypes of the dengue virus (DEN 1, DEN 2, DEN 3 and DEN 4). The symptoms of the illness only appear 3–14 days after the mosquito bite and not immediately. Dengue fever is a flu-like illness that affects infants, young children and adults alike." A more severe manifestation of this illness, Dengue hemorrhagic fever, tends to affect children under 10 years of age which can cause abdominal pain, bleeding and affect the circulatory system.